From 8feb9e80477376a529b8c5ce9951e78f6048f054 Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Sat, 11 Feb 2017 22:36:31 +0100
Subject: [PATCH 01/17] Add SharedRwLock<T> and Locked<T>

---
 components/style/lib.rs         |   3 +
 components/style/shared_lock.rs | 162 ++++++++++++++++++++++++++++++++
 2 files changed, 165 insertions(+)
 create mode 100644 components/style/shared_lock.rs

diff --git a/components/style/lib.rs b/components/style/lib.rs
index b5bc9f74440..58dcafe9ceb 100644
--- a/components/style/lib.rs
+++ b/components/style/lib.rs
@@ -106,6 +106,7 @@ pub mod restyle_hints;
 pub mod rule_tree;
 pub mod scoped_tls;
 pub mod selector_parser;
+pub mod shared_lock;
 pub mod stylist;
 #[cfg(feature = "servo")] #[allow(unsafe_code)] pub mod servo;
 pub mod sequential;
@@ -168,6 +169,8 @@ macro_rules! reexport_computed_values {
 longhand_properties_idents!(reexport_computed_values);
 
 /// Returns whether the two arguments point to the same value.
+///
+/// FIXME: Remove this and use Arc::ptr_eq once we require Rust 1.17
 #[inline]
 pub fn arc_ptr_eq<T: 'static>(a: &Arc<T>, b: &Arc<T>) -> bool {
     let a: &T = &**a;
diff --git a/components/style/shared_lock.rs b/components/style/shared_lock.rs
new file mode 100644
index 00000000000..4565e6e5f69
--- /dev/null
+++ b/components/style/shared_lock.rs
@@ -0,0 +1,162 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Different objects protected by the same lock
+
+use parking_lot::RwLock;
+use std::cell::UnsafeCell;
+use std::fmt;
+use std::sync::Arc;
+
+/// A shared read/write lock that can protect multiple objects.
+#[derive(Clone)]
+#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+pub struct SharedRwLock {
+    #[cfg_attr(feature = "servo", ignore_heap_size_of = "Arc")]
+    arc: Arc<RwLock<()>>,
+}
+
+impl fmt::Debug for SharedRwLock {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str("SharedRwLock")
+    }
+}
+
+impl SharedRwLock {
+    /// Create a new shared lock
+    pub fn new() -> Self {
+        SharedRwLock {
+            arc: Arc::new(RwLock::new(()))
+        }
+    }
+
+    /// Wrap the given data to make its access protected by this lock.
+    pub fn wrap<T>(&self, data: T) -> Locked<T> {
+        Locked {
+            shared_lock: self.clone(),
+            data: UnsafeCell::new(data),
+        }
+    }
+
+    /// Obtain the lock for reading
+    pub fn read(&self) -> SharedRwLockReadGuard {
+        self.arc.raw_read();
+        SharedRwLockReadGuard {
+            shared_lock: self
+        }
+    }
+
+    /// Obtain the lock for writing
+    pub fn write(&self) -> SharedRwLockWriteGuard {
+        self.arc.raw_write();
+        SharedRwLockWriteGuard {
+            shared_lock: self
+        }
+    }
+}
+
+/// Data protect by a shared lock.
+pub struct Locked<T> {
+    shared_lock: SharedRwLock,
+    data: UnsafeCell<T>,
+}
+
+// Unsafe: the data inside `UnsafeCell` is only accessed in `read_with` and `write_with`,
+// where guards ensure synchronization.
+unsafe impl<T: Send> Send for Locked<T> {}
+unsafe impl<T: Send + Sync> Sync for Locked<T> {}
+
+impl<T: fmt::Debug> fmt::Debug for Locked<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let guard = self.shared_lock.read();
+        self.read_with(&guard).fmt(f)
+    }
+}
+
+impl<T> Locked<T> {
+    fn same_lock_as(&self, lock: &SharedRwLock) -> bool {
+        ::arc_ptr_eq(&self.shared_lock.arc, &lock.arc)
+    }
+
+    /// Access the data for reading.
+    pub fn read_with<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> &'a T {
+        assert!(self.same_lock_as(&guard.shared_lock),
+                "Locked::read_with called with a guard from an unrelated SharedRwLock");
+        let ptr = self.data.get();
+
+        // Unsafe:
+        //
+        // * The guard guarantees that the lock is taken for reading,
+        //   and we’ve checked that it’s the correct lock.
+        // * The returned reference borrows *both* the data and the guard,
+        //   so that it can outlive neither.
+        unsafe {
+            &*ptr
+        }
+    }
+
+    /// Access the data for writing.
+    pub fn write_with<'a>(&'a self, guard: &'a mut SharedRwLockWriteGuard) -> &'a mut T {
+        assert!(self.same_lock_as(&guard.shared_lock),
+                "Locked::write_with called with a guard from an unrelated SharedRwLock");
+        let ptr = self.data.get();
+
+        // Unsafe:
+        //
+        // * The guard guarantees that the lock is taken for writing,
+        //   and we’ve checked that it’s the correct lock.
+        // * The returned reference borrows *both* the data and the guard,
+        //   so that it can outlive neither.
+        // * We require a mutable borrow of the guard,
+        //   so that one write guard can only be used once at a time.
+        unsafe {
+            &mut *ptr
+        }
+    }
+}
+
+/// Proof that a shared lock was obtained for reading.
+pub struct SharedRwLockReadGuard<'a> {
+    shared_lock: &'a SharedRwLock,
+}
+
+/// Proof that a shared lock was obtained for writing.
+pub struct SharedRwLockWriteGuard<'a> {
+    shared_lock: &'a SharedRwLock,
+}
+
+impl<'a> Drop for SharedRwLockReadGuard<'a> {
+    fn drop(&mut self) {
+        // Unsafe: self.lock is private to this module, only ever set after `raw_read()`,
+        // and never copied or cloned (see `compile_time_assert` below).
+        unsafe {
+            self.shared_lock.arc.raw_unlock_read()
+        }
+    }
+}
+
+impl<'a> Drop for SharedRwLockWriteGuard<'a> {
+    fn drop(&mut self) {
+        // Unsafe: self.lock is private to this module, only ever set after `raw_write()`,
+        // and never copied or cloned (see `compile_time_assert` below).
+        unsafe {
+            self.shared_lock.arc.raw_unlock_write()
+        }
+    }
+}
+
+#[allow(dead_code)]
+mod compile_time_assert {
+    use super::{SharedRwLockReadGuard, SharedRwLockWriteGuard};
+
+    trait Marker1 {}
+    impl<T: Clone> Marker1 for T {}
+    impl<'a> Marker1 for SharedRwLockReadGuard<'a> {}  // Assert SharedRwLockReadGuard: !Clone
+    impl<'a> Marker1 for SharedRwLockWriteGuard<'a> {}  // Assert SharedRwLockWriteGuard: !Clone
+
+    trait Marker2 {}
+    impl<T: Copy> Marker2 for T {}
+    impl<'a> Marker2 for SharedRwLockReadGuard<'a> {}  // Assert SharedRwLockReadGuard: !Copy
+    impl<'a> Marker2 for SharedRwLockWriteGuard<'a> {}  // Assert SharedRwLockWriteGuard: !Copy
+}

From c5a7294e05a3b370981170ea273acb60b6116bc0 Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Tue, 14 Mar 2017 16:09:41 +0100
Subject: [PATCH 02/17] Replace RwLock<MediaList> with
 shared_lock::Locked<MediaList>

---
 components/layout_thread/lib.rs               | 17 ++++++---
 components/script/dom/bindings/trace.rs       |  2 +
 components/script/dom/document.rs             | 16 ++++++++
 components/script/dom/htmlmetaelement.rs      |  5 ++-
 components/script/dom/htmlstyleelement.rs     |  3 +-
 components/script/layout_wrapper.rs           |  5 +++
 components/script/stylesheet_loader.rs        |  2 +
 components/style/encoding_support.rs          |  3 ++
 components/style/stylesheets.rs               | 37 +++++++++++++------
 components/style/stylist.rs                   | 15 +++++---
 ports/geckolib/glue.rs                        | 17 ++++++---
 ports/geckolib/stylesheet_loader.rs           |  5 ++-
 tests/unit/style/media_queries.rs             | 14 ++++---
 tests/unit/style/rule_tree/bench.rs           |  2 +
 tests/unit/style/stylesheets.rs               |  8 ++--
 tests/unit/style/viewport.rs                  |  2 +
 tests/unit/stylo/lib.rs                       |  3 --
 tests/unit/stylo/servo_function_signatures.rs |  3 ++
 18 files changed, 117 insertions(+), 42 deletions(-)

diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index 566d6e437cd..ee374d18fc8 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -115,6 +115,7 @@ use style::logical_geometry::LogicalPoint;
 use style::media_queries::{Device, MediaType};
 use style::parser::ParserContextExtraData;
 use style::servo::restyle_damage::{REFLOW, REFLOW_OUT_OF_FLOW, REPAINT, REPOSITION, STORE_OVERFLOW};
+use style::shared_lock::SharedRwLock;
 use style::stylesheets::{Origin, Stylesheet, UserAgentStylesheets};
 use style::stylist::Stylist;
 use style::thread_state;
@@ -934,6 +935,7 @@ impl LayoutThread {
                              possibly_locked_rw_data: &mut RwData<'a, 'b>) {
         let document = unsafe { ServoLayoutNode::new(&data.document) };
         let document = document.as_document().unwrap();
+        let style_guard = document.style_shared_lock().read();
         self.quirks_mode = Some(document.quirks_mode());
 
         // FIXME(pcwalton): Combine `ReflowGoal` and `ReflowQueryType`. Then remove this assert.
@@ -1010,7 +1012,8 @@ impl LayoutThread {
 
         // Calculate the actual viewport as per DEVICE-ADAPT § 6
         let device = Device::new(MediaType::Screen, initial_viewport);
-        Arc::get_mut(&mut rw_data.stylist).unwrap().set_device(device, &data.document_stylesheets);
+        Arc::get_mut(&mut rw_data.stylist).unwrap()
+            .set_device(device, &style_guard, &data.document_stylesheets);
 
         self.viewport_size =
             rw_data.stylist.viewport_constraints().map_or(current_screen_size, |constraints| {
@@ -1528,7 +1531,8 @@ fn get_root_flow_background_color(flow: &mut Flow) -> webrender_traits::ColorF {
 }
 
 fn get_ua_stylesheets() -> Result<UserAgentStylesheets, &'static str> {
-    fn parse_ua_stylesheet(filename: &'static str) -> Result<Stylesheet, &'static str> {
+    fn parse_ua_stylesheet(shared_lock: &SharedRwLock, filename: &'static str)
+                           -> Result<Stylesheet, &'static str> {
         let res = try!(read_resource_file(filename).map_err(|_| filename));
         Ok(Stylesheet::from_bytes(
             &res,
@@ -1537,26 +1541,29 @@ fn get_ua_stylesheets() -> Result<UserAgentStylesheets, &'static str> {
             None,
             Origin::UserAgent,
             Default::default(),
+            shared_lock.clone(),
             None,
             &StdoutErrorReporter,
             ParserContextExtraData::default()))
     }
 
+    let shared_lock = SharedRwLock::new();
     let mut user_or_user_agent_stylesheets = vec!();
     // FIXME: presentational-hints.css should be at author origin with zero specificity.
     //        (Does it make a difference?)
     for &filename in &["user-agent.css", "servo.css", "presentational-hints.css"] {
-        user_or_user_agent_stylesheets.push(try!(parse_ua_stylesheet(filename)));
+        user_or_user_agent_stylesheets.push(try!(parse_ua_stylesheet(&shared_lock, filename)));
     }
     for &(ref contents, ref url) in &opts::get().user_stylesheets {
         user_or_user_agent_stylesheets.push(Stylesheet::from_bytes(
             &contents, url.clone(), None, None, Origin::User, Default::default(),
-            None, &StdoutErrorReporter, ParserContextExtraData::default()));
+            shared_lock.clone(), None, &StdoutErrorReporter, ParserContextExtraData::default()));
     }
 
-    let quirks_mode_stylesheet = try!(parse_ua_stylesheet("quirks-mode.css"));
+    let quirks_mode_stylesheet = try!(parse_ua_stylesheet(&shared_lock, "quirks-mode.css"));
 
     Ok(UserAgentStylesheets {
+        shared_lock: shared_lock,
         user_or_user_agent_stylesheets: user_or_user_agent_stylesheets,
         quirks_mode_stylesheet: quirks_mode_stylesheet,
     })
diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index 4d38b39d333..b0828ab6d56 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -99,6 +99,7 @@ use style::keyframes::Keyframe;
 use style::media_queries::MediaList;
 use style::properties::PropertyDeclarationBlock;
 use style::selector_parser::{PseudoElement, Snapshot};
+use style::shared_lock::SharedRwLock as StyleSharedRwLock;
 use style::stylesheets::{CssRules, KeyframesRule, MediaRule, NamespaceRule, StyleRule, ImportRule};
 use style::stylesheets::SupportsRule;
 use style::values::specified::Length;
@@ -360,6 +361,7 @@ unsafe_no_jsmanaged_fields!(HttpsState);
 unsafe_no_jsmanaged_fields!(Request);
 unsafe_no_jsmanaged_fields!(RequestInit);
 unsafe_no_jsmanaged_fields!(SharedRt);
+unsafe_no_jsmanaged_fields!(StyleSharedRwLock);
 unsafe_no_jsmanaged_fields!(TouchpadPressurePhase);
 unsafe_no_jsmanaged_fields!(USVString);
 unsafe_no_jsmanaged_fields!(ReferrerPolicy);
diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index b85366a27d2..7a50fe5cf6c 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -134,6 +134,7 @@ use style::attr::AttrValue;
 use style::context::{QuirksMode, ReflowGoal};
 use style::restyle_hints::{RestyleHint, RESTYLE_STYLE_ATTRIBUTE};
 use style::selector_parser::{RestyleDamage, Snapshot};
+use style::shared_lock::SharedRwLock as StyleSharedRwLock;
 use style::str::{HTML_SPACE_CHARACTERS, split_html_space_chars, str_join};
 use style::stylesheets::Stylesheet;
 use task_source::TaskSource;
@@ -220,6 +221,9 @@ pub struct Document {
     scripts: MutNullableJS<HTMLCollection>,
     anchors: MutNullableJS<HTMLCollection>,
     applets: MutNullableJS<HTMLCollection>,
+    /// Lock use for style attributes and author-origin stylesheet objects in this document.
+    /// Can be acquired once for accessing many objects.
+    style_shared_lock: StyleSharedRwLock,
     /// List of stylesheets associated with nodes in this document. |None| if the list needs to be refreshed.
     stylesheets: DOMRefCell<Option<Vec<StylesheetInDocument>>>,
     /// Whether the list of stylesheets has changed since the last reflow was triggered.
@@ -1964,6 +1968,7 @@ pub trait LayoutDocumentHelpers {
     unsafe fn needs_paint_from_layout(&self);
     unsafe fn will_paint(&self);
     unsafe fn quirks_mode(&self) -> QuirksMode;
+    unsafe fn style_shared_lock(&self) -> &StyleSharedRwLock;
 }
 
 #[allow(unsafe_code)]
@@ -2000,6 +2005,11 @@ impl LayoutDocumentHelpers for LayoutJS<Document> {
     unsafe fn quirks_mode(&self) -> QuirksMode {
         (*self.unsafe_get()).quirks_mode()
     }
+
+    #[inline]
+    unsafe fn style_shared_lock(&self) -> &StyleSharedRwLock {
+        (*self.unsafe_get()).style_shared_lock()
+    }
 }
 
 // https://html.spec.whatwg.org/multipage/#is-a-registrable-domain-suffix-of-or-is-equal-to
@@ -2121,6 +2131,7 @@ impl Document {
             scripts: Default::default(),
             anchors: Default::default(),
             applets: Default::default(),
+            style_shared_lock: StyleSharedRwLock::new(),
             stylesheets: DOMRefCell::new(None),
             stylesheets_changed_since_reflow: Cell::new(false),
             stylesheet_list: MutNullableJS::new(None),
@@ -2250,6 +2261,11 @@ impl Document {
         };
     }
 
+    /// Return a reference to the per-document shared lock used in stylesheets.
+    pub fn style_shared_lock(&self) -> &StyleSharedRwLock {
+        &self.style_shared_lock
+    }
+
     /// Returns the list of stylesheets associated with nodes in the document.
     pub fn stylesheets(&self) -> Vec<Arc<Stylesheet>> {
         self.ensure_stylesheets();
diff --git a/components/script/dom/htmlmetaelement.rs b/components/script/dom/htmlmetaelement.rs
index a751486de7d..2f78e74d3b4 100644
--- a/components/script/dom/htmlmetaelement.rs
+++ b/components/script/dom/htmlmetaelement.rs
@@ -99,12 +99,15 @@ impl HTMLMetaElement {
             let content = content.value();
             if !content.is_empty() {
                 if let Some(translated_rule) = ViewportRule::from_meta(&**content) {
+                    let document = self.upcast::<Node>().owner_doc();
+                    let shared_lock = document.style_shared_lock();
                     *self.stylesheet.borrow_mut() = Some(Arc::new(Stylesheet {
                         rules: CssRules::new(vec![CssRule::Viewport(Arc::new(RwLock::new(translated_rule)))]),
                         origin: Origin::Author,
+                        shared_lock: shared_lock.clone(),
                         base_url: window_from_node(self).get_url(),
                         namespaces: Default::default(),
-                        media: Default::default(),
+                        media: Arc::new(shared_lock.wrap(Default::default())),
                         // Viewport constraints are always recomputed on resize; they don't need to
                         // force all styles to be recomputed.
                         dirty_on_viewport_size_change: AtomicBool::new(false),
diff --git a/components/script/dom/htmlstyleelement.rs b/components/script/dom/htmlstyleelement.rs
index f9c6412f854..13721feba58 100644
--- a/components/script/dom/htmlstyleelement.rs
+++ b/components/script/dom/htmlstyleelement.rs
@@ -84,9 +84,10 @@ impl HTMLStyleElement {
 
         let data = node.GetTextContent().expect("Element.textContent must be a string");
         let mq = parse_media_query_list(&mut CssParser::new(&mq_str));
+        let shared_lock = node.owner_doc().style_shared_lock().clone();
         let loader = StylesheetLoader::for_element(self.upcast());
         let sheet = Stylesheet::from_str(&data, url, Origin::Author, mq,
-                                         Some(&loader),
+                                         shared_lock, Some(&loader),
                                          win.css_error_reporter(),
                                          ParserContextExtraData::default());
 
diff --git a/components/script/layout_wrapper.rs b/components/script/layout_wrapper.rs
index 98ce86745f2..5a9a834667b 100644
--- a/components/script/layout_wrapper.rs
+++ b/components/script/layout_wrapper.rs
@@ -69,6 +69,7 @@ use style::dom::UnsafeNode;
 use style::element_state::*;
 use style::properties::{ComputedValues, PropertyDeclarationBlock};
 use style::selector_parser::{NonTSPseudoClass, PseudoElement, SelectorImpl};
+use style::shared_lock::SharedRwLock as StyleSharedRwLock;
 use style::sink::Push;
 use style::str::is_whitespace;
 use style::stylist::ApplicableDeclarationBlock;
@@ -330,6 +331,10 @@ impl<'ld> ServoLayoutDocument<'ld> {
         unsafe { self.document.quirks_mode() }
     }
 
+    pub fn style_shared_lock(&self) -> &StyleSharedRwLock {
+        unsafe { self.document.style_shared_lock() }
+    }
+
     pub fn from_layout_js(doc: LayoutJS<Document>) -> ServoLayoutDocument<'ld> {
         ServoLayoutDocument {
             document: doc,
diff --git a/components/script/stylesheet_loader.rs b/components/script/stylesheet_loader.rs
index cdc93c9808b..26dffa5fe56 100644
--- a/components/script/stylesheet_loader.rs
+++ b/components/script/stylesheet_loader.rs
@@ -152,12 +152,14 @@ impl FetchResponseListener for StylesheetContext {
                     let is_stylesheet_load_applicable =
                         self.request_generation_id.map_or(true, |gen| gen == link.get_request_generation_id());
                     if is_stylesheet_load_applicable {
+                        let shared_lock = document.style_shared_lock().clone();
                         let sheet =
                             Arc::new(Stylesheet::from_bytes(&data, final_url,
                                                             protocol_encoding_label,
                                                             Some(environment_encoding),
                                                             Origin::Author,
                                                             media.take().unwrap(),
+                                                            shared_lock,
                                                             Some(&loader),
                                                             win.css_error_reporter(),
                                                             ParserContextExtraData::default()));
diff --git a/components/style/encoding_support.rs b/components/style/encoding_support.rs
index 62323ec2314..141291c896e 100644
--- a/components/style/encoding_support.rs
+++ b/components/style/encoding_support.rs
@@ -12,6 +12,7 @@ use media_queries::MediaList;
 use parser::ParserContextExtraData;
 use self::encoding::{EncodingRef, DecoderTrap};
 use servo_url::ServoUrl;
+use shared_lock::SharedRwLock;
 use std::str;
 use stylesheets::{Stylesheet, StylesheetLoader, Origin};
 
@@ -54,6 +55,7 @@ impl Stylesheet {
                       environment_encoding: Option<EncodingRef>,
                       origin: Origin,
                       media: MediaList,
+                      shared_lock: SharedRwLock,
                       stylesheet_loader: Option<&StylesheetLoader>,
                       error_reporter: &ParseErrorReporter,
                       extra_data: ParserContextExtraData)
@@ -64,6 +66,7 @@ impl Stylesheet {
                              base_url,
                              origin,
                              media,
+                             shared_lock,
                              stylesheet_loader,
                              error_reporter,
                              extra_data)
diff --git a/components/style/stylesheets.rs b/components/style/stylesheets.rs
index 5b5c47e152f..3d487ec8db1 100644
--- a/components/style/stylesheets.rs
+++ b/components/style/stylesheets.rs
@@ -21,6 +21,7 @@ use selector_parser::{SelectorImpl, SelectorParser};
 use selectors::parser::SelectorList;
 use servo_config::prefs::PREFS;
 use servo_url::ServoUrl;
+use shared_lock::{SharedRwLock, Locked, SharedRwLockReadGuard};
 use std::cell::Cell;
 use std::fmt;
 use std::sync::Arc;
@@ -175,11 +176,13 @@ pub struct Stylesheet {
     /// cascading order)
     pub rules: Arc<RwLock<CssRules>>,
     /// List of media associated with the Stylesheet.
-    pub media: Arc<RwLock<MediaList>>,
+    pub media: Arc<Locked<MediaList>>,
     /// The origin of this stylesheet.
     pub origin: Origin,
     /// The base url this stylesheet should use.
     pub base_url: ServoUrl,
+    /// The lock used for objects inside this stylesheet
+    pub shared_lock: SharedRwLock,
     /// The namespaces that apply to this stylesheet.
     pub namespaces: RwLock<Namespaces>,
     /// Whether this stylesheet would be dirty when the viewport size changes.
@@ -191,6 +194,8 @@ pub struct Stylesheet {
 
 /// This structure holds the user-agent and user stylesheets.
 pub struct UserAgentStylesheets {
+    /// The lock used for user-agent stylesheets.
+    pub shared_lock: SharedRwLock,
     /// The user or user agent stylesheets.
     pub user_or_user_agent_stylesheets: Vec<Stylesheet>,
     /// The quirks mode stylesheet.
@@ -291,12 +296,12 @@ impl CssRule {
     /// used for others.
     ///
     /// This will not recurse down unsupported @supports rules
-    pub fn with_nested_rules_and_mq<F, R>(&self, mut f: F) -> R
+    pub fn with_nested_rules_and_mq<F, R>(&self, guard: &SharedRwLockReadGuard, mut f: F) -> R
     where F: FnMut(&[CssRule], Option<&MediaList>) -> R {
         match *self {
             CssRule::Import(ref lock) => {
                 let rule = lock.read();
-                let media = rule.stylesheet.media.read();
+                let media = rule.stylesheet.media.read_with(guard);
                 let rules = rule.stylesheet.rules.read();
                 // FIXME(emilio): Include the nested rules if the stylesheet is
                 // loaded.
@@ -349,6 +354,7 @@ impl CssRule {
         let mut rule_parser = TopLevelRuleParser {
             stylesheet_origin: parent_stylesheet.origin,
             context: context,
+            shared_lock: &parent_stylesheet.shared_lock,
             loader: None,
             state: Cell::new(state),
             namespaces: &mut namespaces,
@@ -424,7 +430,8 @@ impl ToCss for ImportRule {
     fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
         try!(dest.write_str("@import "));
         try!(self.url.to_css(dest));
-        let media = self.stylesheet.media.read();
+        let guard = self.stylesheet.shared_lock.read();  // FIXME: have the caller pass this?
+        let media = self.stylesheet.media.read_with(&guard);
         if !media.is_empty() {
             try!(dest.write_str(" "));
             try!(media.to_css(dest));
@@ -554,6 +561,7 @@ impl Stylesheet {
         let rule_parser = TopLevelRuleParser {
             stylesheet_origin: existing.origin,
             namespaces: &mut namespaces,
+            shared_lock: &existing.shared_lock,
             loader: stylesheet_loader,
             context: ParserContext::new_with_extra_data(existing.origin,
                                                         &existing.base_url,
@@ -591,6 +599,7 @@ impl Stylesheet {
                     base_url: ServoUrl,
                     origin: Origin,
                     media: MediaList,
+                    shared_lock: SharedRwLock,
                     stylesheet_loader: Option<&StylesheetLoader>,
                     error_reporter: &ParseErrorReporter,
                     extra_data: ParserContextExtraData) -> Stylesheet {
@@ -599,7 +608,8 @@ impl Stylesheet {
             base_url: base_url,
             namespaces: RwLock::new(Namespaces::default()),
             rules: CssRules::new(vec![]),
-            media: Arc::new(RwLock::new(media)),
+            media: Arc::new(shared_lock.wrap(media)),
+            shared_lock: shared_lock.clone(),
             dirty_on_viewport_size_change: AtomicBool::new(false),
             disabled: AtomicBool::new(false),
         };
@@ -638,7 +648,8 @@ impl Stylesheet {
     ///
     /// Always true if no associated MediaList exists.
     pub fn is_effective_for_device(&self, device: &Device) -> bool {
-        self.media.read().evaluate(device)
+        let guard = self.shared_lock.read();  // FIXME: have the caller pass this?
+        self.media.read_with(&guard).evaluate(device)
     }
 
     /// Return an iterator over the effective rules within the style-sheet, as
@@ -649,7 +660,8 @@ impl Stylesheet {
     /// examined.
     #[inline]
     pub fn effective_rules<F>(&self, device: &Device, mut f: F) where F: FnMut(&CssRule) {
-        effective_rules(&self.rules.read().0, device, &mut f);
+        let guard = self.shared_lock.read();  // FIXME: have the caller pass this?
+        effective_rules(&self.rules.read().0, device, &guard, &mut f);
     }
 
     /// Returns whether the stylesheet has been explicitly disabled through the
@@ -670,16 +682,17 @@ impl Stylesheet {
     }
 }
 
-fn effective_rules<F>(rules: &[CssRule], device: &Device, f: &mut F) where F: FnMut(&CssRule) {
+fn effective_rules<F>(rules: &[CssRule], device: &Device, guard: &SharedRwLockReadGuard, f: &mut F)
+where F: FnMut(&CssRule) {
     for rule in rules {
         f(rule);
-        rule.with_nested_rules_and_mq(|rules, mq| {
+        rule.with_nested_rules_and_mq(guard, |rules, mq| {
             if let Some(media_queries) = mq {
                 if !media_queries.evaluate(device) {
                     return
                 }
             }
-            effective_rules(rules, device, f)
+            effective_rules(rules, device, guard, f)
         })
     }
 }
@@ -724,6 +737,7 @@ pub trait StylesheetLoader {
 struct TopLevelRuleParser<'a> {
     stylesheet_origin: Origin,
     namespaces: &'a mut Namespaces,
+    shared_lock: &'a SharedRwLock,
     loader: Option<&'a StylesheetLoader>,
     context: ParserContext<'a>,
     state: Cell<State>,
@@ -780,7 +794,7 @@ impl<'a> AtRuleParser for TopLevelRuleParser<'a> {
                                                              &self.context));
 
                     let media =
-                        Arc::new(RwLock::new(parse_media_query_list(input)));
+                        Arc::new(self.shared_lock.wrap(parse_media_query_list(input)));
 
                     let is_valid_url = url.url().is_some();
 
@@ -790,6 +804,7 @@ impl<'a> AtRuleParser for TopLevelRuleParser<'a> {
                             stylesheet: Arc::new(Stylesheet {
                                 rules: Arc::new(RwLock::new(CssRules(vec![]))),
                                 media: media,
+                                shared_lock: self.shared_lock.clone(),
                                 origin: self.context.stylesheet_origin,
                                 base_url: self.context.base_url.clone(),
                                 namespaces: RwLock::new(Namespaces::default()),
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index f7dd149e7d3..e28bb641cd0 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -28,6 +28,7 @@ use selectors::matching::{AFFECTED_BY_STYLE_ATTRIBUTE, AFFECTED_BY_PRESENTATIONA
 use selectors::matching::{ElementSelectorFlags, StyleRelations, matches_complex_selector};
 use selectors::parser::{Selector, SimpleSelector, LocalName as LocalNameSelector, ComplexSelector};
 use selectors::parser::SelectorMethods;
+#[cfg(feature = "servo")] use shared_lock::SharedRwLockReadGuard;
 use sink::Push;
 use smallvec::VecLike;
 use std::borrow::Borrow;
@@ -461,7 +462,8 @@ impl Stylist {
     /// FIXME(emilio): The semantics of the device for Servo and Gecko are
     /// different enough we may want to unify them.
     #[cfg(feature = "servo")]
-    pub fn set_device(&mut self, mut device: Device, stylesheets: &[Arc<Stylesheet>]) {
+    pub fn set_device(&mut self, mut device: Device, guard: &SharedRwLockReadGuard,
+                      stylesheets: &[Arc<Stylesheet>]) {
         let cascaded_rule = ViewportRule {
             declarations: viewport::Cascade::from_stylesheets(stylesheets, &device).finish(),
         };
@@ -473,15 +475,16 @@ impl Stylist {
             device.account_for_viewport_rule(constraints);
         }
 
-        fn mq_eval_changed(rules: &[CssRule], before: &Device, after: &Device) -> bool {
+        fn mq_eval_changed(guard: &SharedRwLockReadGuard, rules: &[CssRule],
+                           before: &Device, after: &Device) -> bool {
             for rule in rules {
-                let changed = rule.with_nested_rules_and_mq(|rules, mq| {
+                let changed = rule.with_nested_rules_and_mq(guard, |rules, mq| {
                     if let Some(mq) = mq {
                         if mq.evaluate(before) != mq.evaluate(after) {
                             return true
                         }
                     }
-                    mq_eval_changed(rules, before, after)
+                    mq_eval_changed(guard, rules, before, after)
                 });
                 if changed {
                     return true
@@ -490,12 +493,12 @@ impl Stylist {
             false
         }
         self.is_device_dirty |= stylesheets.iter().any(|stylesheet| {
-            let mq = stylesheet.media.read();
+            let mq = stylesheet.media.read_with(guard);
             if mq.evaluate(&self.device) != mq.evaluate(&device) {
                 return true
             }
 
-            mq_eval_changed(&stylesheet.rules.read().0, &self.device, &device)
+            mq_eval_changed(guard, &stylesheet.rules.read().0, &self.device, &device)
         });
 
         self.device = Arc::new(device);
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index 16d8b0c9f36..7330d8f63de 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -76,6 +76,7 @@ use style::properties::parse_one_declaration;
 use style::restyle_hints::{self, RestyleHint};
 use style::selector_parser::PseudoElementCascadeType;
 use style::sequential;
+use style::shared_lock::SharedRwLock;
 use style::string_cache::Atom;
 use style::stylesheets::{CssRule, CssRules, ImportRule, MediaRule, NamespaceRule};
 use style::stylesheets::{Origin, Stylesheet, StyleRule};
@@ -85,7 +86,7 @@ use style::thread_state;
 use style::timer::Timer;
 use style::traversal::{resolve_style, DomTraversal, TraversalDriver};
 use style_traits::ToCss;
-use stylesheet_loader::StylesheetLoader;
+use super::stylesheet_loader::StylesheetLoader;
 
 /*
  * For Gecko->Servo function calls, we need to redeclare the same signature that was declared in
@@ -95,12 +96,15 @@ use stylesheet_loader::StylesheetLoader;
  * depend on but good enough for our purposes.
  */
 
-struct GlobalStyleData {
+pub struct GlobalStyleData {
     // How many threads parallel styling can use.
     pub num_threads: usize,
 
     // The parallel styling thread pool.
     pub style_thread_pool: Option<rayon::ThreadPool>,
+
+    // Shared RWLock for CSSOM objects
+    pub shared_lock: SharedRwLock,
 }
 
 impl GlobalStyleData {
@@ -124,12 +128,13 @@ impl GlobalStyleData {
         GlobalStyleData {
             num_threads: num_threads,
             style_thread_pool: pool,
+            shared_lock: SharedRwLock::new(),
         }
     }
 }
 
 lazy_static! {
-    static ref GLOBAL_STYLE_DATA: GlobalStyleData = {
+    pub static ref GLOBAL_STYLE_DATA: GlobalStyleData = {
         GlobalStyleData::new()
     };
 }
@@ -335,8 +340,9 @@ pub extern "C" fn Servo_StyleSheet_Empty(mode: SheetParsingMode) -> RawServoStyl
         SheetParsingMode::eUserSheetFeatures => Origin::User,
         SheetParsingMode::eAgentSheetFeatures => Origin::UserAgent,
     };
+    let shared_lock = GLOBAL_STYLE_DATA.shared_lock.clone();
     Arc::new(Stylesheet::from_str(
-        "", url, origin, Default::default(), None,
+        "", url, origin, Default::default(), shared_lock, None,
         &StdoutErrorReporter, extra_data)
     ).into_strong()
 }
@@ -378,8 +384,9 @@ pub extern "C" fn Servo_StyleSheet_FromUTF8Bytes(loader: *mut Loader,
         Some(ref s) => Some(s),
     };
 
+    let shared_lock = GLOBAL_STYLE_DATA.shared_lock.clone();
     Arc::new(Stylesheet::from_str(
-        input, url, origin, Default::default(), loader,
+        input, url, origin, Default::default(), shared_lock, loader,
         &StdoutErrorReporter, extra_data)
     ).into_strong()
 }
diff --git a/ports/geckolib/stylesheet_loader.rs b/ports/geckolib/stylesheet_loader.rs
index 3e6fb421c86..bcd55cce2fd 100644
--- a/ports/geckolib/stylesheet_loader.rs
+++ b/ports/geckolib/stylesheet_loader.rs
@@ -9,6 +9,7 @@ use style::gecko_bindings::structs::{Loader, ServoStyleSheet};
 use style::gecko_bindings::sugar::ownership::HasArcFFI;
 use style::stylesheets::{ImportRule, StylesheetLoader as StyleStylesheetLoader};
 use style_traits::ToCss;
+use super::glue::GLOBAL_STYLE_DATA;
 
 pub struct StylesheetLoader(*mut Loader, *mut ServoStyleSheet);
 
@@ -20,6 +21,8 @@ impl StylesheetLoader {
 
 impl StyleStylesheetLoader for StylesheetLoader {
     fn request_stylesheet(&self, import_rule: &Arc<RwLock<ImportRule>>) {
+        let global_style_data = &*GLOBAL_STYLE_DATA;
+        let guard = global_style_data.shared_lock.read();
         let import = import_rule.read();
         let (spec_bytes, spec_len) = import.url.as_slice_components()
             .expect("Import only loads valid URLs");
@@ -32,7 +35,7 @@ impl StyleStylesheetLoader for StylesheetLoader {
         // evaluate them on the main thread.
         //
         // Meanwhile, this works.
-        let media = import.stylesheet.media.read().to_css_string();
+        let media = import.stylesheet.media.read_with(&guard).to_css_string();
 
         unsafe {
             Gecko_LoadStyleSheet(self.0,
diff --git a/tests/unit/style/media_queries.rs b/tests/unit/style/media_queries.rs
index 95182676e3c..485ccd1d486 100644
--- a/tests/unit/style/media_queries.rs
+++ b/tests/unit/style/media_queries.rs
@@ -11,6 +11,7 @@ use style::error_reporting::ParseErrorReporter;
 use style::media_queries::*;
 use style::parser::ParserContextExtraData;
 use style::servo::media_queries::*;
+use style::shared_lock::{SharedRwLock, SharedRwLockReadGuard};
 use style::stylesheets::{Stylesheet, Origin, CssRule};
 use style::values::specified;
 use style_traits::ToCss;
@@ -29,26 +30,27 @@ fn test_media_rule<F>(css: &str, callback: F)
     let url = ServoUrl::parse("http://localhost").unwrap();
     let css_str = css.to_owned();
     let stylesheet = Stylesheet::from_str(
-        css, url, Origin::Author, Default::default(),
+        css, url, Origin::Author, Default::default(), SharedRwLock::new(),
         None, &CSSErrorReporterTest,
         ParserContextExtraData::default());
     let mut rule_count = 0;
-    media_queries(&stylesheet.rules.read().0, &mut |mq| {
+    let guard = stylesheet.shared_lock.read();
+    media_queries(&guard, &stylesheet.rules.read().0, &mut |mq| {
         rule_count += 1;
         callback(mq, css);
     });
     assert!(rule_count > 0, css_str);
 }
 
-fn media_queries<F>(rules: &[CssRule], f: &mut F)
+fn media_queries<F>(guard: &SharedRwLockReadGuard, rules: &[CssRule], f: &mut F)
     where F: FnMut(&MediaList),
 {
     for rule in rules {
-        rule.with_nested_rules_and_mq(|rules, mq| {
+        rule.with_nested_rules_and_mq(guard, |rules, mq| {
             if let Some(mq) = mq {
                 f(mq)
             }
-            media_queries(rules, f)
+            media_queries(guard, rules, f)
         })
     }
 }
@@ -56,7 +58,7 @@ fn media_queries<F>(rules: &[CssRule], f: &mut F)
 fn media_query_test(device: &Device, css: &str, expected_rule_count: usize) {
     let url = ServoUrl::parse("http://localhost").unwrap();
     let ss = Stylesheet::from_str(
-        css, url, Origin::Author, Default::default(),
+        css, url, Origin::Author, Default::default(), SharedRwLock::new(),
         None, &CSSErrorReporterTest,
         ParserContextExtraData::default());
     let mut rule_count = 0;
diff --git a/tests/unit/style/rule_tree/bench.rs b/tests/unit/style/rule_tree/bench.rs
index 37bef590a64..623a534159a 100644
--- a/tests/unit/style/rule_tree/bench.rs
+++ b/tests/unit/style/rule_tree/bench.rs
@@ -12,6 +12,7 @@ use style::media_queries::MediaList;
 use style::parser::ParserContextExtraData;
 use style::properties::{longhands, Importance, PropertyDeclaration, PropertyDeclarationBlock};
 use style::rule_tree::{CascadeLevel, RuleTree, StrongRuleNode, StyleSource};
+use style::shared_lock::SharedRwLock;
 use style::stylesheets::{Origin, Stylesheet, CssRule};
 use test::{self, Bencher};
 
@@ -44,6 +45,7 @@ fn parse_rules(css: &str) -> Vec<(StyleSource, CascadeLevel)> {
                                  MediaList {
                                      media_queries: vec![],
                                  },
+                                 SharedRwLock::new(),
                                  None,
                                  &ErrorringErrorReporter,
                                  ParserContextExtraData {});
diff --git a/tests/unit/style/stylesheets.rs b/tests/unit/style/stylesheets.rs
index a1d649c099c..590e93185f4 100644
--- a/tests/unit/style/stylesheets.rs
+++ b/tests/unit/style/stylesheets.rs
@@ -20,6 +20,7 @@ use style::properties::Importance;
 use style::properties::{CSSWideKeyword, DeclaredValueOwned, PropertyDeclaration, PropertyDeclarationBlock};
 use style::properties::longhands;
 use style::properties::longhands::animation_play_state;
+use style::shared_lock::SharedRwLock;
 use style::stylesheets::{Origin, Namespaces};
 use style::stylesheets::{Stylesheet, NamespaceRule, CssRule, CssRules, StyleRule, KeyframesRule};
 use style::values::specified::{LengthOrPercentageOrAuto, Percentage};
@@ -62,14 +63,15 @@ fn test_parse_stylesheet() {
         }";
     let url = ServoUrl::parse("about::test").unwrap();
     let stylesheet = Stylesheet::from_str(css, url.clone(), Origin::UserAgent, Default::default(),
-                                          None,
+                                          SharedRwLock::new(), None,
                                           &CSSErrorReporterTest,
                                           ParserContextExtraData::default());
     let mut namespaces = Namespaces::default();
     namespaces.default = Some(ns!(html));
     let expected = Stylesheet {
         origin: Origin::UserAgent,
-        media: Default::default(),
+        media: Arc::new(stylesheet.shared_lock.wrap(Default::default())),
+        shared_lock: stylesheet.shared_lock.clone(),
         namespaces: RwLock::new(namespaces),
         base_url: url,
         dirty_on_viewport_size_change: AtomicBool::new(false),
@@ -324,7 +326,7 @@ fn test_report_error_stylesheet() {
     let errors = error_reporter.errors.clone();
 
     Stylesheet::from_str(css, url.clone(), Origin::UserAgent, Default::default(),
-                         None,
+                         SharedRwLock::new(), None,
                          &error_reporter,
                          ParserContextExtraData::default());
 
diff --git a/tests/unit/style/viewport.rs b/tests/unit/style/viewport.rs
index 166094ebdc1..9fe53ebb40c 100644
--- a/tests/unit/style/viewport.rs
+++ b/tests/unit/style/viewport.rs
@@ -9,6 +9,7 @@ use servo_config::prefs::{PREFS, PrefValue};
 use servo_url::ServoUrl;
 use style::media_queries::{Device, MediaType};
 use style::parser::{ParserContext, ParserContextExtraData};
+use style::shared_lock::SharedRwLock;
 use style::stylesheets::{Stylesheet, Origin};
 use style::values::specified::LengthOrPercentageOrAuto::{self, Auto};
 use style::values::specified::NoCalcLength::{self, ViewportPercentage};
@@ -24,6 +25,7 @@ macro_rules! stylesheet {
             ServoUrl::parse("http://localhost").unwrap(),
             Origin::$origin,
             Default::default(),
+            SharedRwLock::new(),
             None,
             &$error_reporter,
             ParserContextExtraData::default()
diff --git a/tests/unit/stylo/lib.rs b/tests/unit/stylo/lib.rs
index c89687918ef..c0d04ffcbec 100644
--- a/tests/unit/stylo/lib.rs
+++ b/tests/unit/stylo/lib.rs
@@ -21,8 +21,5 @@ extern crate style_traits;
 mod sanity_checks;
 mod size_of;
 
-#[path = "../../../ports/geckolib/stylesheet_loader.rs"]
-mod stylesheet_loader;
-
 mod servo_function_signatures;
 
diff --git a/tests/unit/stylo/servo_function_signatures.rs b/tests/unit/stylo/servo_function_signatures.rs
index 6bdeb6d5af7..30d6d02439b 100644
--- a/tests/unit/stylo/servo_function_signatures.rs
+++ b/tests/unit/stylo/servo_function_signatures.rs
@@ -10,6 +10,9 @@ use style::gecko_properties::*;
 
 include!(concat!(env!("OUT_DIR"), "/check_bindings.rs"));
 
+#[path = "../../../ports/geckolib/stylesheet_loader.rs"]
+mod stylesheet_loader;
+
 #[allow(non_snake_case, unused_unsafe, private_no_mangle_fns)]
 mod glue {
     // this module pretends to be glue.rs, with the safe functions swapped for unsafe ones. This is

From d18b1280f2a5f660fa8e40dbcb3c0923a7703d58 Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Thu, 16 Mar 2017 23:08:10 +0100
Subject: [PATCH 03/17] Move shared lock acquires up the call stack. (Or is it
 down?)

---
 components/layout_thread/lib.rs | 11 +++++++----
 components/style/gecko/data.rs  |  9 +++++----
 components/style/stylesheets.rs |  5 ++---
 components/style/stylist.rs     | 16 +++++++++-------
 ports/geckolib/glue.rs          | 32 +++++++++++++++++++++++---------
 5 files changed, 46 insertions(+), 27 deletions(-)

diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index ee374d18fc8..c86c0221603 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -731,7 +731,8 @@ impl LayoutThread {
         // GWTODO: Need to handle unloading web fonts.
 
         let rw_data = possibly_locked_rw_data.lock();
-        if stylesheet.is_effective_for_device(&rw_data.stylist.device) {
+        let guard = stylesheet.shared_lock.read();
+        if stylesheet.is_effective_for_device(&rw_data.stylist.device, &guard) {
             add_font_face_rules(&*stylesheet,
                                 &rw_data.stylist.device,
                                 &self.font_cache_thread,
@@ -1057,9 +1058,11 @@ impl LayoutThread {
         }
 
         // If the entire flow tree is invalid, then it will be reflowed anyhow.
-        let needs_dirtying = Arc::get_mut(&mut rw_data.stylist).unwrap().update(&data.document_stylesheets,
-                                                                                 Some(&*UA_STYLESHEETS),
-                                                                                 data.stylesheets_changed);
+        let needs_dirtying = Arc::get_mut(&mut rw_data.stylist).unwrap().update(
+            &data.document_stylesheets,
+            &style_guard,
+            Some(&*UA_STYLESHEETS),
+            data.stylesheets_changed);
         let needs_reflow = viewport_size_changed && !needs_dirtying;
         if needs_dirtying {
             if let Some(mut d) = element.mutate_data() {
diff --git a/components/style/gecko/data.rs b/components/style/gecko/data.rs
index 627b3845051..e0f7df023e2 100644
--- a/components/style/gecko/data.rs
+++ b/components/style/gecko/data.rs
@@ -13,6 +13,7 @@ use gecko_bindings::sugar::ownership::{HasBoxFFI, HasFFI, HasSimpleFFI};
 use media_queries::Device;
 use parking_lot::RwLock;
 use properties::ComputedValues;
+use shared_lock::SharedRwLockReadGuard;
 use std::collections::HashMap;
 use std::sync::Arc;
 use std::sync::mpsc::{Receiver, Sender, channel};
@@ -83,20 +84,20 @@ impl PerDocumentStyleDataImpl {
     /// Reset the device state because it may have changed.
     ///
     /// Implies also a stylesheet flush.
-    pub fn reset_device(&mut self) {
+    pub fn reset_device(&mut self, guard: &SharedRwLockReadGuard) {
         {
             let mut stylist = Arc::get_mut(&mut self.stylist).unwrap();
             Arc::get_mut(&mut stylist.device).unwrap().reset();
         }
         self.stylesheets_changed = true;
-        self.flush_stylesheets();
+        self.flush_stylesheets(guard);
     }
 
     /// Recreate the style data if the stylesheets have changed.
-    pub fn flush_stylesheets(&mut self) {
+    pub fn flush_stylesheets(&mut self, guard: &SharedRwLockReadGuard) {
         if self.stylesheets_changed {
             let mut stylist = Arc::get_mut(&mut self.stylist).unwrap();
-            stylist.update(&self.stylesheets, None, true);
+            stylist.update(&self.stylesheets, guard, None, true);
             self.stylesheets_changed = false;
         }
     }
diff --git a/components/style/stylesheets.rs b/components/style/stylesheets.rs
index 3d487ec8db1..092bbdf8a93 100644
--- a/components/style/stylesheets.rs
+++ b/components/style/stylesheets.rs
@@ -647,9 +647,8 @@ impl Stylesheet {
     /// on the associated MediaList.
     ///
     /// Always true if no associated MediaList exists.
-    pub fn is_effective_for_device(&self, device: &Device) -> bool {
-        let guard = self.shared_lock.read();  // FIXME: have the caller pass this?
-        self.media.read_with(&guard).evaluate(device)
+    pub fn is_effective_for_device(&self, device: &Device, guard: &SharedRwLockReadGuard) -> bool {
+        self.media.read_with(guard).evaluate(device)
     }
 
     /// Return an iterator over the effective rules within the style-sheet, as
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index e28bb641cd0..27adfdd451a 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -28,7 +28,7 @@ use selectors::matching::{AFFECTED_BY_STYLE_ATTRIBUTE, AFFECTED_BY_PRESENTATIONA
 use selectors::matching::{ElementSelectorFlags, StyleRelations, matches_complex_selector};
 use selectors::parser::{Selector, SimpleSelector, LocalName as LocalNameSelector, ComplexSelector};
 use selectors::parser::SelectorMethods;
-#[cfg(feature = "servo")] use shared_lock::SharedRwLockReadGuard;
+use shared_lock::SharedRwLockReadGuard;
 use sink::Push;
 use smallvec::VecLike;
 use std::borrow::Borrow;
@@ -159,6 +159,7 @@ impl Stylist {
     /// device is dirty, which means we need to re-evaluate media queries.
     pub fn update(&mut self,
                   doc_stylesheets: &[Arc<Stylesheet>],
+                  doc_guard: &SharedRwLockReadGuard,
                   ua_stylesheets: Option<&UserAgentStylesheets>,
                   stylesheets_changed: bool) -> bool {
         if !(self.is_device_dirty || stylesheets_changed) {
@@ -193,17 +194,18 @@ impl Stylist {
         self.non_common_style_affecting_attributes_selectors.clear();
 
         if let Some(ua_stylesheets) = ua_stylesheets {
+            let ua_guard = ua_stylesheets.shared_lock.read();
             for stylesheet in &ua_stylesheets.user_or_user_agent_stylesheets {
-                self.add_stylesheet(&stylesheet);
+                self.add_stylesheet(&stylesheet, &ua_guard);
             }
 
             if self.quirks_mode {
-                self.add_stylesheet(&ua_stylesheets.quirks_mode_stylesheet);
+                self.add_stylesheet(&ua_stylesheets.quirks_mode_stylesheet, &ua_guard);
             }
         }
 
         for ref stylesheet in doc_stylesheets.iter() {
-            self.add_stylesheet(stylesheet);
+            self.add_stylesheet(stylesheet, doc_guard);
         }
 
         debug!("Stylist stats:");
@@ -227,8 +229,8 @@ impl Stylist {
         true
     }
 
-    fn add_stylesheet(&mut self, stylesheet: &Stylesheet) {
-        if stylesheet.disabled() || !stylesheet.is_effective_for_device(&self.device) {
+    fn add_stylesheet(&mut self, stylesheet: &Stylesheet, guard: &SharedRwLockReadGuard) {
+        if stylesheet.disabled() || !stylesheet.is_effective_for_device(&self.device, guard) {
             return;
         }
 
@@ -271,7 +273,7 @@ impl Stylist {
                 }
                 CssRule::Import(ref import) => {
                     let import = import.read();
-                    self.add_stylesheet(&import.stylesheet)
+                    self.add_stylesheet(&import.stylesheet, guard)
                 }
                 CssRule::Keyframes(ref keyframes_rule) => {
                     let keyframes_rule = keyframes_rule.read();
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index 7330d8f63de..b8c6e4ebbab 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -204,7 +204,7 @@ fn traverse_subtree(element: GeckoElement, raw_data: RawServoStyleSetBorrowed,
     debug!("{:?}", ShowSubtreeData(element.as_node()));
 
     let shared_style_context = create_shared_context(&per_doc_data);
-    let ref global_style_data = *GLOBAL_STYLE_DATA;
+    let global_style_data = &*GLOBAL_STYLE_DATA;
 
     let traversal_driver = if global_style_data.style_thread_pool.is_none() {
         TraversalDriver::Sequential
@@ -333,6 +333,7 @@ pub extern "C" fn Servo_Element_ClearData(element: RawGeckoElementBorrowed) {
 
 #[no_mangle]
 pub extern "C" fn Servo_StyleSheet_Empty(mode: SheetParsingMode) -> RawServoStyleSheetStrong {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
     let url = ServoUrl::parse("about:blank").unwrap();
     let extra_data = ParserContextExtraData::default();
     let origin = match mode {
@@ -340,7 +341,7 @@ pub extern "C" fn Servo_StyleSheet_Empty(mode: SheetParsingMode) -> RawServoStyl
         SheetParsingMode::eUserSheetFeatures => Origin::User,
         SheetParsingMode::eAgentSheetFeatures => Origin::UserAgent,
     };
-    let shared_lock = GLOBAL_STYLE_DATA.shared_lock.clone();
+    let shared_lock = global_style_data.shared_lock.clone();
     Arc::new(Stylesheet::from_str(
         "", url, origin, Default::default(), shared_lock, None,
         &StdoutErrorReporter, extra_data)
@@ -357,6 +358,7 @@ pub extern "C" fn Servo_StyleSheet_FromUTF8Bytes(loader: *mut Loader,
                                                  referrer: *mut ThreadSafeURIHolder,
                                                  principal: *mut ThreadSafePrincipalHolder)
                                                  -> RawServoStyleSheetStrong {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
     let input = unsafe { data.as_ref().unwrap().as_str_unchecked() };
 
     let origin = match mode {
@@ -384,7 +386,7 @@ pub extern "C" fn Servo_StyleSheet_FromUTF8Bytes(loader: *mut Loader,
         Some(ref s) => Some(s),
     };
 
-    let shared_lock = GLOBAL_STYLE_DATA.shared_lock.clone();
+    let shared_lock = global_style_data.shared_lock.clone();
     Arc::new(Stylesheet::from_str(
         input, url, origin, Default::default(), shared_lock, loader,
         &StdoutErrorReporter, extra_data)
@@ -430,13 +432,15 @@ pub extern "C" fn Servo_StyleSheet_ClearAndUpdate(stylesheet: RawServoStyleSheet
 pub extern "C" fn Servo_StyleSet_AppendStyleSheet(raw_data: RawServoStyleSetBorrowed,
                                                   raw_sheet: RawServoStyleSheetBorrowed,
                                                   flush: bool) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
     let mut data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
     let sheet = HasArcFFI::as_arc(&raw_sheet);
     data.stylesheets.retain(|x| !arc_ptr_eq(x, sheet));
     data.stylesheets.push(sheet.clone());
     data.stylesheets_changed = true;
     if flush {
-        data.flush_stylesheets();
+        data.flush_stylesheets(&guard);
     }
 }
 
@@ -444,13 +448,15 @@ pub extern "C" fn Servo_StyleSet_AppendStyleSheet(raw_data: RawServoStyleSetBorr
 pub extern "C" fn Servo_StyleSet_PrependStyleSheet(raw_data: RawServoStyleSetBorrowed,
                                                    raw_sheet: RawServoStyleSheetBorrowed,
                                                    flush: bool) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
     let mut data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
     let sheet = HasArcFFI::as_arc(&raw_sheet);
     data.stylesheets.retain(|x| !arc_ptr_eq(x, sheet));
     data.stylesheets.insert(0, sheet.clone());
     data.stylesheets_changed = true;
     if flush {
-        data.flush_stylesheets();
+        data.flush_stylesheets(&guard);
     }
 }
 
@@ -459,6 +465,8 @@ pub extern "C" fn Servo_StyleSet_InsertStyleSheetBefore(raw_data: RawServoStyleS
                                                         raw_sheet: RawServoStyleSheetBorrowed,
                                                         raw_reference: RawServoStyleSheetBorrowed,
                                                         flush: bool) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
     let mut data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
     let sheet = HasArcFFI::as_arc(&raw_sheet);
     let reference = HasArcFFI::as_arc(&raw_reference);
@@ -467,7 +475,7 @@ pub extern "C" fn Servo_StyleSet_InsertStyleSheetBefore(raw_data: RawServoStyleS
     data.stylesheets.insert(index, sheet.clone());
     data.stylesheets_changed = true;
     if flush {
-        data.flush_stylesheets();
+        data.flush_stylesheets(&guard);
     }
 }
 
@@ -475,19 +483,23 @@ pub extern "C" fn Servo_StyleSet_InsertStyleSheetBefore(raw_data: RawServoStyleS
 pub extern "C" fn Servo_StyleSet_RemoveStyleSheet(raw_data: RawServoStyleSetBorrowed,
                                                   raw_sheet: RawServoStyleSheetBorrowed,
                                                   flush: bool) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
     let mut data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
     let sheet = HasArcFFI::as_arc(&raw_sheet);
     data.stylesheets.retain(|x| !arc_ptr_eq(x, sheet));
     data.stylesheets_changed = true;
     if flush {
-        data.flush_stylesheets();
+        data.flush_stylesheets(&guard);
     }
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_StyleSet_FlushStyleSheets(raw_data: RawServoStyleSetBorrowed) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
     let mut data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
-    data.flush_stylesheets();
+    data.flush_stylesheets(&guard);
 }
 
 #[no_mangle]
@@ -732,8 +744,10 @@ pub extern "C" fn Servo_StyleSet_Init(pres_context: RawGeckoPresContextOwned)
 
 #[no_mangle]
 pub extern "C" fn Servo_StyleSet_RebuildData(raw_data: RawServoStyleSetBorrowed) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
     let mut data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
-    data.reset_device();
+    data.reset_device(&guard);
 }
 
 #[no_mangle]

From 3ae2ecbec2f2a22734e078555614ce7ac3e761a3 Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Thu, 16 Mar 2017 23:42:39 +0100
Subject: [PATCH 04/17] More lock acquire in callers

---
 components/layout_thread/lib.rs   | 13 +++++++++----
 components/style/stylesheets.rs   | 11 ++++++-----
 components/style/stylist.rs       |  8 +++++---
 components/style/viewport.rs      |  6 ++++--
 tests/unit/style/media_queries.rs |  2 +-
 tests/unit/style/viewport.rs      | 30 ++++++++++++++++++++----------
 6 files changed, 45 insertions(+), 25 deletions(-)

diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index c86c0221603..566d6c7ca33 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -115,7 +115,7 @@ use style::logical_geometry::LogicalPoint;
 use style::media_queries::{Device, MediaType};
 use style::parser::ParserContextExtraData;
 use style::servo::restyle_damage::{REFLOW, REFLOW_OUT_OF_FLOW, REPAINT, REPOSITION, STORE_OVERFLOW};
-use style::shared_lock::SharedRwLock;
+use style::shared_lock::{SharedRwLock, SharedRwLockReadGuard};
 use style::stylesheets::{Origin, Stylesheet, UserAgentStylesheets};
 use style::stylist::Stylist;
 use style::thread_state;
@@ -345,13 +345,14 @@ impl<'a, 'b: 'a> RwData<'a, 'b> {
 }
 
 fn add_font_face_rules(stylesheet: &Stylesheet,
+                       guard: &SharedRwLockReadGuard,
                        device: &Device,
                        font_cache_thread: &FontCacheThread,
                        font_cache_sender: &IpcSender<()>,
                        outstanding_web_fonts_counter: &Arc<AtomicUsize>) {
     if opts::get().load_webfonts_synchronously {
         let (sender, receiver) = ipc::channel().unwrap();
-        stylesheet.effective_font_face_rules(&device, |font_face| {
+        stylesheet.effective_font_face_rules(&device, guard, |font_face| {
             let effective_sources = font_face.effective_sources();
             font_cache_thread.add_web_font(font_face.family.clone(),
                                            effective_sources,
@@ -359,7 +360,7 @@ fn add_font_face_rules(stylesheet: &Stylesheet,
             receiver.recv().unwrap();
         })
     } else {
-        stylesheet.effective_font_face_rules(&device, |font_face| {
+        stylesheet.effective_font_face_rules(&device, guard, |font_face| {
             let effective_sources = font_face.effective_sources();
             outstanding_web_fonts_counter.fetch_add(1, Ordering::SeqCst);
             font_cache_thread.add_web_font(font_face.family.clone(),
@@ -407,8 +408,11 @@ impl LayoutThread {
 
         let stylist = Arc::new(Stylist::new(device));
         let outstanding_web_fonts_counter = Arc::new(AtomicUsize::new(0));
-        for stylesheet in &*UA_STYLESHEETS.user_or_user_agent_stylesheets {
+        let ua_stylesheets = &*UA_STYLESHEETS;
+        let guard = ua_stylesheets.shared_lock.read();
+        for stylesheet in &ua_stylesheets.user_or_user_agent_stylesheets {
             add_font_face_rules(stylesheet,
+                                &guard,
                                 &stylist.device,
                                 &font_cache_thread,
                                 &ipc_font_cache_sender,
@@ -734,6 +738,7 @@ impl LayoutThread {
         let guard = stylesheet.shared_lock.read();
         if stylesheet.is_effective_for_device(&rw_data.stylist.device, &guard) {
             add_font_face_rules(&*stylesheet,
+                                &guard,
                                 &rw_data.stylist.device,
                                 &self.font_cache_thread,
                                 &self.font_cache_sender,
diff --git a/components/style/stylesheets.rs b/components/style/stylesheets.rs
index 092bbdf8a93..6c6862fef5e 100644
--- a/components/style/stylesheets.rs
+++ b/components/style/stylesheets.rs
@@ -658,9 +658,9 @@ impl Stylesheet {
     /// nested rules will be skipped. Use `rules` if all rules need to be
     /// examined.
     #[inline]
-    pub fn effective_rules<F>(&self, device: &Device, mut f: F) where F: FnMut(&CssRule) {
-        let guard = self.shared_lock.read();  // FIXME: have the caller pass this?
-        effective_rules(&self.rules.read().0, device, &guard, &mut f);
+    pub fn effective_rules<F>(&self, device: &Device, guard: &SharedRwLockReadGuard, mut f: F)
+    where F: FnMut(&CssRule) {
+        effective_rules(&self.rules.read().0, device, guard, &mut f);
     }
 
     /// Returns whether the stylesheet has been explicitly disabled through the
@@ -701,8 +701,9 @@ macro_rules! rule_filter {
         impl Stylesheet {
             $(
                 #[allow(missing_docs)]
-                pub fn $method<F>(&self, device: &Device, mut f: F) where F: FnMut(&$rule_type) {
-                    self.effective_rules(device, |rule| {
+                pub fn $method<F>(&self, device: &Device, guard: &SharedRwLockReadGuard, mut f: F)
+                where F: FnMut(&$rule_type) {
+                    self.effective_rules(device, guard, |rule| {
                         if let CssRule::$variant(ref lock) = *rule {
                             let rule = lock.read();
                             f(&rule)
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index 27adfdd451a..0ff9d20d883 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -167,7 +167,9 @@ impl Stylist {
         }
 
         let cascaded_rule = ViewportRule {
-            declarations: viewport::Cascade::from_stylesheets(doc_stylesheets, &self.device).finish(),
+            declarations: viewport::Cascade::from_stylesheets(
+                doc_stylesheets, doc_guard, &self.device
+            ).finish(),
         };
 
         self.viewport_constraints =
@@ -237,7 +239,7 @@ impl Stylist {
         // Cheap `Arc` clone so that the closure below can borrow `&mut Stylist`.
         let device = self.device.clone();
 
-        stylesheet.effective_rules(&device, |rule| {
+        stylesheet.effective_rules(&device, guard, |rule| {
             match *rule {
                 CssRule::Style(ref style_rule) => {
                     let guard = style_rule.read();
@@ -467,7 +469,7 @@ impl Stylist {
     pub fn set_device(&mut self, mut device: Device, guard: &SharedRwLockReadGuard,
                       stylesheets: &[Arc<Stylesheet>]) {
         let cascaded_rule = ViewportRule {
-            declarations: viewport::Cascade::from_stylesheets(stylesheets, &device).finish(),
+            declarations: viewport::Cascade::from_stylesheets(stylesheets, guard, &device).finish(),
         };
 
         self.viewport_constraints =
diff --git a/components/style/viewport.rs b/components/style/viewport.rs
index 9c364dc7249..196216423f0 100644
--- a/components/style/viewport.rs
+++ b/components/style/viewport.rs
@@ -15,6 +15,7 @@ use cssparser::ToCss as ParserToCss;
 use euclid::size::TypedSize2D;
 use media_queries::Device;
 use parser::{ParserContext, log_css_error};
+use shared_lock::SharedRwLockReadGuard;
 use std::ascii::AsciiExt;
 use std::borrow::Cow;
 use std::fmt;
@@ -555,13 +556,14 @@ impl Cascade {
         }
     }
 
-    pub fn from_stylesheets<'a, I>(stylesheets: I, device: &Device) -> Self
+    pub fn from_stylesheets<'a, I>(stylesheets: I, guard: &SharedRwLockReadGuard,
+                                   device: &Device) -> Self
         where I: IntoIterator,
               I::Item: AsRef<Stylesheet>,
     {
         let mut cascade = Self::new();
         for stylesheet in stylesheets {
-            stylesheet.as_ref().effective_viewport_rules(device, |rule| {
+            stylesheet.as_ref().effective_viewport_rules(device, guard, |rule| {
                 for declaration in &rule.declarations {
                     cascade.add(Cow::Borrowed(declaration))
                 }
diff --git a/tests/unit/style/media_queries.rs b/tests/unit/style/media_queries.rs
index 485ccd1d486..652d68ce953 100644
--- a/tests/unit/style/media_queries.rs
+++ b/tests/unit/style/media_queries.rs
@@ -62,7 +62,7 @@ fn media_query_test(device: &Device, css: &str, expected_rule_count: usize) {
         None, &CSSErrorReporterTest,
         ParserContextExtraData::default());
     let mut rule_count = 0;
-    ss.effective_style_rules(device, |_| rule_count += 1);
+    ss.effective_style_rules(device, &ss.shared_lock.read(), |_| rule_count += 1);
     assert!(rule_count == expected_rule_count, css.to_owned());
 }
 
diff --git a/tests/unit/style/viewport.rs b/tests/unit/style/viewport.rs
index 9fe53ebb40c..7423286227d 100644
--- a/tests/unit/style/viewport.rs
+++ b/tests/unit/style/viewport.rs
@@ -20,12 +20,15 @@ use style_traits::viewport::*;
 
 macro_rules! stylesheet {
     ($css:expr, $origin:ident, $error_reporter:expr) => {
+        stylesheet!($css, $origin, $error_reporter, SharedRwLock::new())
+    };
+    ($css:expr, $origin:ident, $error_reporter:expr, $shared_lock:expr) => {
         Box::new(Stylesheet::from_str(
             $css,
             ServoUrl::parse("http://localhost").unwrap(),
             Origin::$origin,
             Default::default(),
-            SharedRwLock::new(),
+            $shared_lock,
             None,
             &$error_reporter,
             ParserContextExtraData::default()
@@ -41,7 +44,7 @@ fn test_viewport_rule<F>(css: &str,
     PREFS.set("layout.viewport.enabled", PrefValue::Boolean(true));
     let stylesheet = stylesheet!(css, Author, CSSErrorReporterTest);
     let mut rule_count = 0;
-    stylesheet.effective_viewport_rules(&device, |rule| {
+    stylesheet.effective_viewport_rules(&device, &stylesheet.shared_lock.read(), |rule| {
         rule_count += 1;
         callback(&rule.declarations, css);
     });
@@ -253,24 +256,31 @@ fn multiple_stylesheets_cascading() {
     PREFS.set("layout.viewport.enabled", PrefValue::Boolean(true));
     let device = Device::new(MediaType::Screen, TypedSize2D::new(800., 600.));
     let error_reporter = CSSErrorReporterTest;
+    let shared_lock = SharedRwLock::new();
     let stylesheets = vec![
-        stylesheet!("@viewport { min-width: 100px; min-height: 100px; zoom: 1; }", UserAgent, error_reporter),
-        stylesheet!("@viewport { min-width: 200px; min-height: 200px; }", User, error_reporter),
-        stylesheet!("@viewport { min-width: 300px; }", Author, error_reporter)];
+        stylesheet!("@viewport { min-width: 100px; min-height: 100px; zoom: 1; }",
+                    UserAgent, error_reporter, shared_lock.clone()),
+        stylesheet!("@viewport { min-width: 200px; min-height: 200px; }",
+                    User, error_reporter, shared_lock.clone()),
+        stylesheet!("@viewport { min-width: 300px; }",
+                    Author, error_reporter, shared_lock.clone())
+    ];
 
-    let declarations = Cascade::from_stylesheets(&stylesheets, &device).finish();
+    let declarations = Cascade::from_stylesheets(&stylesheets, &shared_lock.read(), &device).finish();
     assert_decl_len!(declarations == 3);
     assert_decl_eq!(&declarations[0], UserAgent, Zoom: Zoom::Number(1.));
     assert_decl_eq!(&declarations[1], User, MinHeight: viewport_length!(200., px));
     assert_decl_eq!(&declarations[2], Author, MinWidth: viewport_length!(300., px));
 
     let stylesheets = vec![
-        stylesheet!("@viewport { min-width: 100px !important; }", UserAgent, error_reporter),
+        stylesheet!("@viewport { min-width: 100px !important; }",
+                    UserAgent, error_reporter, shared_lock.clone()),
         stylesheet!("@viewport { min-width: 200px !important; min-height: 200px !important; }",
-        User, error_reporter),
+                    User, error_reporter, shared_lock.clone()),
         stylesheet!("@viewport { min-width: 300px !important; min-height: 300px !important; zoom: 3 !important; }",
-        Author, error_reporter)];
-    let declarations = Cascade::from_stylesheets(&stylesheets, &device).finish();
+                    Author, error_reporter, shared_lock.clone())
+    ];
+    let declarations = Cascade::from_stylesheets(&stylesheets, &shared_lock.read(), &device).finish();
     assert_decl_len!(declarations == 3);
     assert_decl_eq!(&declarations[0], UserAgent, MinWidth: viewport_length!(100., px), !important);
     assert_decl_eq!(&declarations[1], User, MinHeight: viewport_length!(200., px), !important);

From fe4e70c5f8b05778c09aed0b1d8a727cc1066df3 Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Fri, 17 Mar 2017 00:19:09 +0100
Subject: [PATCH 05/17] Introduce a ToCssWithGuard trait

---
 components/script/dom/cssconditionrule.rs |  4 ++
 components/script/dom/cssfontfacerule.rs  |  5 +-
 components/script/dom/cssgroupingrule.rs  |  5 ++
 components/script/dom/cssimportrule.rs    |  5 +-
 components/script/dom/csskeyframesrule.rs |  5 +-
 components/script/dom/cssmediarule.rs     |  8 +--
 components/script/dom/cssnamespacerule.rs |  5 +-
 components/script/dom/cssrule.rs          |  5 ++
 components/script/dom/cssstylerule.rs     |  5 +-
 components/script/dom/csssupportsrule.rs  |  8 +--
 components/script/dom/cssviewportrule.rs  |  5 +-
 components/style/font_face.rs             |  8 +--
 components/style/shared_lock.rs           | 17 +++++++
 components/style/stylesheets.rs           | 60 +++++++++++++----------
 components/style/viewport.rs              |  7 +--
 ports/geckolib/glue.rs                    |  6 ++-
 16 files changed, 104 insertions(+), 54 deletions(-)

diff --git a/components/script/dom/cssconditionrule.rs b/components/script/dom/cssconditionrule.rs
index 02c52bcf28f..42fca721759 100644
--- a/components/script/dom/cssconditionrule.rs
+++ b/components/script/dom/cssconditionrule.rs
@@ -12,6 +12,7 @@ use dom::csssupportsrule::CSSSupportsRule;
 use dom_struct::dom_struct;
 use parking_lot::RwLock;
 use std::sync::Arc;
+use style::shared_lock::SharedRwLock;
 use style::stylesheets::CssRules as StyleCssRules;
 
 #[dom_struct]
@@ -27,6 +28,9 @@ impl CSSConditionRule {
         }
     }
 
+    pub fn shared_lock(&self) -> &SharedRwLock {
+        self.cssgroupingrule.shared_lock()
+    }
 }
 
 impl CSSConditionRuleMethods for CSSConditionRule {
diff --git a/components/script/dom/cssfontfacerule.rs b/components/script/dom/cssfontfacerule.rs
index b9ef949c1b7..4556f90a56c 100644
--- a/components/script/dom/cssfontfacerule.rs
+++ b/components/script/dom/cssfontfacerule.rs
@@ -12,8 +12,8 @@ use dom::window::Window;
 use dom_struct::dom_struct;
 use parking_lot::RwLock;
 use std::sync::Arc;
+use style::shared_lock::ToCssWithGuard;
 use style::font_face::FontFaceRule;
-use style_traits::ToCss;
 
 #[dom_struct]
 pub struct CSSFontFaceRule {
@@ -47,6 +47,7 @@ impl SpecificCSSRule for CSSFontFaceRule {
     }
 
     fn get_css(&self) -> DOMString {
-        self.fontfacerule.read().to_css_string().into()
+        let guard = self.cssrule.shared_lock().read();
+        self.fontfacerule.read().to_css_string(&guard).into()
     }
 }
diff --git a/components/script/dom/cssgroupingrule.rs b/components/script/dom/cssgroupingrule.rs
index ec608b2bc77..29f6bc361a2 100644
--- a/components/script/dom/cssgroupingrule.rs
+++ b/components/script/dom/cssgroupingrule.rs
@@ -14,6 +14,7 @@ use dom::cssstylesheet::CSSStyleSheet;
 use dom_struct::dom_struct;
 use parking_lot::RwLock;
 use std::sync::Arc;
+use style::shared_lock::SharedRwLock;
 use style::stylesheets::CssRules as StyleCssRules;
 
 #[dom_struct]
@@ -40,6 +41,10 @@ impl CSSGroupingRule {
                                                   parent_stylesheet,
                                                   RulesSource::Rules(self.rules.clone())))
     }
+
+    pub fn shared_lock(&self) -> &SharedRwLock {
+        self.cssrule.shared_lock()
+    }
 }
 
 impl CSSGroupingRuleMethods for CSSGroupingRule {
diff --git a/components/script/dom/cssimportrule.rs b/components/script/dom/cssimportrule.rs
index 6ef354ec43e..bb01fdfcc84 100644
--- a/components/script/dom/cssimportrule.rs
+++ b/components/script/dom/cssimportrule.rs
@@ -12,8 +12,8 @@ use dom::window::Window;
 use dom_struct::dom_struct;
 use parking_lot::RwLock;
 use std::sync::Arc;
+use style::shared_lock::ToCssWithGuard;
 use style::stylesheets::ImportRule;
-use style_traits::ToCss;
 
 #[dom_struct]
 pub struct CSSImportRule {
@@ -49,6 +49,7 @@ impl SpecificCSSRule for CSSImportRule {
     }
 
     fn get_css(&self) -> DOMString {
-        self.import_rule.read().to_css_string().into()
+        let guard = self.cssrule.shared_lock().read();
+        self.import_rule.read().to_css_string(&guard).into()
     }
 }
diff --git a/components/script/dom/csskeyframesrule.rs b/components/script/dom/csskeyframesrule.rs
index db0240bf9a2..330b1be3627 100644
--- a/components/script/dom/csskeyframesrule.rs
+++ b/components/script/dom/csskeyframesrule.rs
@@ -21,8 +21,8 @@ use servo_atoms::Atom;
 use std::sync::Arc;
 use style::keyframes::{Keyframe, KeyframeSelector};
 use style::parser::ParserContextExtraData;
+use style::shared_lock::ToCssWithGuard;
 use style::stylesheets::KeyframesRule;
-use style_traits::ToCss;
 
 #[dom_struct]
 pub struct CSSKeyframesRule {
@@ -134,7 +134,8 @@ impl SpecificCSSRule for CSSKeyframesRule {
     }
 
     fn get_css(&self) -> DOMString {
-        self.keyframesrule.read().to_css_string().into()
+        let guard = self.cssrule.shared_lock().read();
+        self.keyframesrule.read().to_css_string(&guard).into()
     }
 
     fn deparent_children(&self) {
diff --git a/components/script/dom/cssmediarule.rs b/components/script/dom/cssmediarule.rs
index 31923cb29dd..9242ee01bb7 100644
--- a/components/script/dom/cssmediarule.rs
+++ b/components/script/dom/cssmediarule.rs
@@ -17,12 +17,13 @@ use dom_struct::dom_struct;
 use parking_lot::RwLock;
 use std::sync::Arc;
 use style::media_queries::parse_media_query_list;
+use style::shared_lock::ToCssWithGuard;
 use style::stylesheets::MediaRule;
 use style_traits::ToCss;
 
 #[dom_struct]
 pub struct CSSMediaRule {
-    cssrule: CSSConditionRule,
+    cssconditionrule: CSSConditionRule,
     #[ignore_heap_size_of = "Arc"]
     mediarule: Arc<RwLock<MediaRule>>,
     medialist: MutNullableJS<MediaList>,
@@ -33,7 +34,7 @@ impl CSSMediaRule {
                      -> CSSMediaRule {
         let list = mediarule.read().rules.clone();
         CSSMediaRule {
-            cssrule: CSSConditionRule::new_inherited(parent_stylesheet, list),
+            cssconditionrule: CSSConditionRule::new_inherited(parent_stylesheet, list),
             mediarule: mediarule,
             medialist: MutNullableJS::new(None),
         }
@@ -76,7 +77,8 @@ impl SpecificCSSRule for CSSMediaRule {
     }
 
     fn get_css(&self) -> DOMString {
-        self.mediarule.read().to_css_string().into()
+        let guard = self.cssconditionrule.shared_lock().read();
+        self.mediarule.read().to_css_string(&guard).into()
     }
 }
 
diff --git a/components/script/dom/cssnamespacerule.rs b/components/script/dom/cssnamespacerule.rs
index 51f60fafd08..46702c275ba 100644
--- a/components/script/dom/cssnamespacerule.rs
+++ b/components/script/dom/cssnamespacerule.rs
@@ -13,8 +13,8 @@ use dom::window::Window;
 use dom_struct::dom_struct;
 use parking_lot::RwLock;
 use std::sync::Arc;
+use style::shared_lock::ToCssWithGuard;
 use style::stylesheets::NamespaceRule;
-use style_traits::ToCss;
 
 #[dom_struct]
 pub struct CSSNamespaceRule {
@@ -62,6 +62,7 @@ impl SpecificCSSRule for CSSNamespaceRule {
     }
 
     fn get_css(&self) -> DOMString {
-        self.namespacerule.read().to_css_string().into()
+        let guard = self.cssrule.shared_lock().read();
+        self.namespacerule.read().to_css_string(&guard).into()
     }
 }
diff --git a/components/script/dom/cssrule.rs b/components/script/dom/cssrule.rs
index 277d7323a21..54bb8c175a5 100644
--- a/components/script/dom/cssrule.rs
+++ b/components/script/dom/cssrule.rs
@@ -20,6 +20,7 @@ use dom::cssviewportrule::CSSViewportRule;
 use dom::window::Window;
 use dom_struct::dom_struct;
 use std::cell::Cell;
+use style::shared_lock::SharedRwLock;
 use style::stylesheets::CssRule as StyleCssRule;
 
 
@@ -103,6 +104,10 @@ impl CSSRule {
     pub fn parent_stylesheet(&self) -> &CSSStyleSheet {
         &self.parent_stylesheet
     }
+
+    pub fn shared_lock(&self) -> &SharedRwLock {
+        &self.parent_stylesheet.style_stylesheet().shared_lock
+    }
 }
 
 impl CSSRuleMethods for CSSRule {
diff --git a/components/script/dom/cssstylerule.rs b/components/script/dom/cssstylerule.rs
index 3c4c8c815d1..2423861e446 100644
--- a/components/script/dom/cssstylerule.rs
+++ b/components/script/dom/cssstylerule.rs
@@ -14,8 +14,8 @@ use dom::window::Window;
 use dom_struct::dom_struct;
 use parking_lot::RwLock;
 use std::sync::Arc;
+use style::shared_lock::ToCssWithGuard;
 use style::stylesheets::StyleRule;
-use style_traits::ToCss;
 
 #[dom_struct]
 pub struct CSSStyleRule {
@@ -51,7 +51,8 @@ impl SpecificCSSRule for CSSStyleRule {
     }
 
     fn get_css(&self) -> DOMString {
-        self.stylerule.read().to_css_string().into()
+        let guard = self.cssrule.shared_lock().read();
+        self.stylerule.read().to_css_string(&guard).into()
     }
 }
 
diff --git a/components/script/dom/csssupportsrule.rs b/components/script/dom/csssupportsrule.rs
index 0cc113bef1c..d5e844e52aa 100644
--- a/components/script/dom/csssupportsrule.rs
+++ b/components/script/dom/csssupportsrule.rs
@@ -16,13 +16,14 @@ use dom_struct::dom_struct;
 use parking_lot::RwLock;
 use std::sync::Arc;
 use style::parser::ParserContext;
+use style::shared_lock::ToCssWithGuard;
 use style::stylesheets::SupportsRule;
 use style::supports::SupportsCondition;
 use style_traits::ToCss;
 
 #[dom_struct]
 pub struct CSSSupportsRule {
-    cssrule: CSSConditionRule,
+    cssconditionrule: CSSConditionRule,
     #[ignore_heap_size_of = "Arc"]
     supportsrule: Arc<RwLock<SupportsRule>>,
 }
@@ -32,7 +33,7 @@ impl CSSSupportsRule {
                      -> CSSSupportsRule {
         let list = supportsrule.read().rules.clone();
         CSSSupportsRule {
-            cssrule: CSSConditionRule::new_inherited(parent_stylesheet, list),
+            cssconditionrule: CSSConditionRule::new_inherited(parent_stylesheet, list),
             supportsrule: supportsrule,
         }
     }
@@ -75,6 +76,7 @@ impl SpecificCSSRule for CSSSupportsRule {
     }
 
     fn get_css(&self) -> DOMString {
-        self.supportsrule.read().to_css_string().into()
+        let guard = self.cssconditionrule.shared_lock().read();
+        self.supportsrule.read().to_css_string(&guard).into()
     }
 }
diff --git a/components/script/dom/cssviewportrule.rs b/components/script/dom/cssviewportrule.rs
index c784a26f442..855c8bdda57 100644
--- a/components/script/dom/cssviewportrule.rs
+++ b/components/script/dom/cssviewportrule.rs
@@ -12,8 +12,8 @@ use dom::window::Window;
 use dom_struct::dom_struct;
 use parking_lot::RwLock;
 use std::sync::Arc;
+use style::shared_lock::ToCssWithGuard;
 use style::viewport::ViewportRule;
-use style_traits::ToCss;
 
 #[dom_struct]
 pub struct CSSViewportRule {
@@ -46,6 +46,7 @@ impl SpecificCSSRule for CSSViewportRule {
     }
 
     fn get_css(&self) -> DOMString {
-        self.viewportrule.read().to_css_string().into()
+        let guard = self.cssrule.shared_lock().read();
+        self.viewportrule.read().to_css_string(&guard).into()
     }
 }
diff --git a/components/style/font_face.rs b/components/style/font_face.rs
index 0d4bc4f8a09..8bad3a93aee 100644
--- a/components/style/font_face.rs
+++ b/components/style/font_face.rs
@@ -14,6 +14,7 @@ use computed_values::font_family::FamilyName;
 use cssparser::{AtRuleParser, DeclarationListParser, DeclarationParser, Parser};
 #[cfg(feature = "gecko")] use cssparser::UnicodeRange;
 use parser::{ParserContext, log_css_error, Parse};
+use shared_lock::{SharedRwLockReadGuard, ToCssWithGuard};
 use std::fmt;
 use std::iter;
 use style_traits::{ToCss, OneOrMoreCommaSeparated};
@@ -230,11 +231,10 @@ macro_rules! font_face_descriptors {
             }
         }
 
-        impl ToCss for FontFaceRule {
+        impl ToCssWithGuard for FontFaceRule {
             // Serialization of FontFaceRule is not specced.
-            fn to_css<W>(&self, dest: &mut W) -> fmt::Result
-                where W: fmt::Write,
-            {
+            fn to_css<W>(&self, _guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
+            where W: fmt::Write {
                 dest.write_str("@font-face {\n")?;
                 $(
                     dest.write_str(concat!("  ", $m_name, ": "))?;
diff --git a/components/style/shared_lock.rs b/components/style/shared_lock.rs
index 4565e6e5f69..d4d66b8fc5d 100644
--- a/components/style/shared_lock.rs
+++ b/components/style/shared_lock.rs
@@ -160,3 +160,20 @@ mod compile_time_assert {
     impl<'a> Marker2 for SharedRwLockReadGuard<'a> {}  // Assert SharedRwLockReadGuard: !Copy
     impl<'a> Marker2 for SharedRwLockWriteGuard<'a> {}  // Assert SharedRwLockWriteGuard: !Copy
 }
+
+/// Like ToCss, but with a lock guard given by the caller.
+pub trait ToCssWithGuard {
+    /// Serialize `self` in CSS syntax, writing to `dest`, using the given lock guard.
+    fn to_css<W>(&self, guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
+    where W: fmt::Write;
+
+    /// Serialize `self` in CSS syntax using the given lock guard and return a string.
+    ///
+    /// (This is a convenience wrapper for `to_css` and probably should not be overridden.)
+    #[inline]
+    fn to_css_string(&self, guard: &SharedRwLockReadGuard) -> String {
+        let mut s = String::new();
+        self.to_css(guard, &mut s).unwrap();
+        s
+    }
+}
diff --git a/components/style/stylesheets.rs b/components/style/stylesheets.rs
index 6c6862fef5e..df6a9641f0d 100644
--- a/components/style/stylesheets.rs
+++ b/components/style/stylesheets.rs
@@ -21,7 +21,7 @@ use selector_parser::{SelectorImpl, SelectorParser};
 use selectors::parser::SelectorList;
 use servo_config::prefs::PREFS;
 use servo_url::ServoUrl;
-use shared_lock::{SharedRwLock, Locked, SharedRwLockReadGuard};
+use shared_lock::{SharedRwLock, Locked, SharedRwLockReadGuard, ToCssWithGuard};
 use std::cell::Cell;
 use std::fmt;
 use std::sync::Arc;
@@ -372,18 +372,19 @@ impl CssRule {
     }
 }
 
-impl ToCss for CssRule {
+impl ToCssWithGuard for CssRule {
     // https://drafts.csswg.org/cssom/#serialize-a-css-rule
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+    fn to_css<W>(&self, guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
+    where W: fmt::Write {
         match *self {
-            CssRule::Namespace(ref lock) => lock.read().to_css(dest),
-            CssRule::Import(ref lock) => lock.read().to_css(dest),
-            CssRule::Style(ref lock) => lock.read().to_css(dest),
-            CssRule::FontFace(ref lock) => lock.read().to_css(dest),
-            CssRule::Viewport(ref lock) => lock.read().to_css(dest),
-            CssRule::Keyframes(ref lock) => lock.read().to_css(dest),
-            CssRule::Media(ref lock) => lock.read().to_css(dest),
-            CssRule::Supports(ref lock) => lock.read().to_css(dest),
+            CssRule::Namespace(ref lock) => lock.read().to_css(guard, dest),
+            CssRule::Import(ref lock) => lock.read().to_css(guard, dest),
+            CssRule::Style(ref lock) => lock.read().to_css(guard, dest),
+            CssRule::FontFace(ref lock) => lock.read().to_css(guard, dest),
+            CssRule::Viewport(ref lock) => lock.read().to_css(guard, dest),
+            CssRule::Keyframes(ref lock) => lock.read().to_css(guard, dest),
+            CssRule::Media(ref lock) => lock.read().to_css(guard, dest),
+            CssRule::Supports(ref lock) => lock.read().to_css(guard, dest),
         }
     }
 }
@@ -396,9 +397,10 @@ pub struct NamespaceRule {
     pub url: Namespace,
 }
 
-impl ToCss for NamespaceRule {
+impl ToCssWithGuard for NamespaceRule {
     // https://drafts.csswg.org/cssom/#serialize-a-css-rule CSSNamespaceRule
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+    fn to_css<W>(&self, _guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
+    where W: fmt::Write {
         try!(dest.write_str("@namespace "));
         if let Some(ref prefix) = self.prefix {
             try!(dest.write_str(&*prefix.to_string()));
@@ -426,12 +428,12 @@ pub struct ImportRule {
     pub stylesheet: Arc<Stylesheet>,
 }
 
-impl ToCss for ImportRule {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+impl ToCssWithGuard for ImportRule {
+    fn to_css<W>(&self, guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
+    where W: fmt::Write {
         try!(dest.write_str("@import "));
         try!(self.url.to_css(dest));
-        let guard = self.stylesheet.shared_lock.read();  // FIXME: have the caller pass this?
-        let media = self.stylesheet.media.read_with(&guard);
+        let media = self.stylesheet.media.read_with(guard);
         if !media.is_empty() {
             try!(dest.write_str(" "));
             try!(media.to_css(dest));
@@ -451,9 +453,10 @@ pub struct KeyframesRule {
     pub keyframes: Vec<Arc<RwLock<Keyframe>>>,
 }
 
-impl ToCss for KeyframesRule {
+impl ToCssWithGuard for KeyframesRule {
     // Serialization of KeyframesRule is not specced.
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+    fn to_css<W>(&self, _guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
+    where W: fmt::Write {
         try!(dest.write_str("@keyframes "));
         try!(dest.write_str(&*self.name.to_string()));
         try!(dest.write_str(" { "));
@@ -478,16 +481,17 @@ pub struct MediaRule {
     pub rules: Arc<RwLock<CssRules>>,
 }
 
-impl ToCss for MediaRule {
+impl ToCssWithGuard for MediaRule {
     // Serialization of MediaRule is not specced.
     // https://drafts.csswg.org/cssom/#serialize-a-css-rule CSSMediaRule
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+    fn to_css<W>(&self, guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
+    where W: fmt::Write {
         try!(dest.write_str("@media "));
         try!(self.media_queries.read().to_css(dest));
         try!(dest.write_str(" {"));
         for rule in self.rules.read().0.iter() {
             try!(dest.write_str(" "));
-            try!(rule.to_css(dest));
+            try!(rule.to_css(guard, dest));
         }
         dest.write_str(" }")
     }
@@ -505,14 +509,15 @@ pub struct SupportsRule {
     pub enabled: bool,
 }
 
-impl ToCss for SupportsRule {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+impl ToCssWithGuard for SupportsRule {
+    fn to_css<W>(&self, guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
+    where W: fmt::Write {
         try!(dest.write_str("@supports "));
         try!(self.condition.to_css(dest));
         try!(dest.write_str(" {"));
         for rule in self.rules.read().0.iter() {
             try!(dest.write_str(" "));
-            try!(rule.to_css(dest));
+            try!(rule.to_css(guard, dest));
         }
         dest.write_str(" }")
     }
@@ -525,9 +530,10 @@ pub struct StyleRule {
     pub block: Arc<RwLock<PropertyDeclarationBlock>>,
 }
 
-impl ToCss for StyleRule {
+impl ToCssWithGuard for StyleRule {
     // https://drafts.csswg.org/cssom/#serialize-a-css-rule CSSStyleRule
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+    fn to_css<W>(&self, _guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
+    where W: fmt::Write {
         // Step 1
         try!(self.selectors.to_css(dest));
         // Step 2
diff --git a/components/style/viewport.rs b/components/style/viewport.rs
index 196216423f0..690c06fd377 100644
--- a/components/style/viewport.rs
+++ b/components/style/viewport.rs
@@ -15,7 +15,7 @@ use cssparser::ToCss as ParserToCss;
 use euclid::size::TypedSize2D;
 use media_queries::Device;
 use parser::{ParserContext, log_css_error};
-use shared_lock::SharedRwLockReadGuard;
+use shared_lock::{SharedRwLockReadGuard, ToCssWithGuard};
 use std::ascii::AsciiExt;
 use std::borrow::Cow;
 use std::fmt;
@@ -505,9 +505,10 @@ impl ViewportRule {
     }
 }
 
-impl ToCss for ViewportRule {
+impl ToCssWithGuard for ViewportRule {
     // Serialization of ViewportRule is not specced.
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+    fn to_css<W>(&self, _guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
+    where W: fmt::Write {
         try!(dest.write_str("@viewport { "));
         let mut iter = self.declarations.iter();
         try!(iter.next().unwrap().to_css(dest));
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index b8c6e4ebbab..cdc0a530f09 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -76,7 +76,7 @@ use style::properties::parse_one_declaration;
 use style::restyle_hints::{self, RestyleHint};
 use style::selector_parser::PseudoElementCascadeType;
 use style::sequential;
-use style::shared_lock::SharedRwLock;
+use style::shared_lock::{SharedRwLock, ToCssWithGuard};
 use style::string_cache::Atom;
 use style::stylesheets::{CssRule, CssRules, ImportRule, MediaRule, NamespaceRule};
 use style::stylesheets::{Origin, Stylesheet, StyleRule};
@@ -581,8 +581,10 @@ macro_rules! impl_basic_rule_funcs {
 
         #[no_mangle]
         pub extern "C" fn $to_css(rule: &$raw_type, result: *mut nsAString) {
+            let global_style_data = &*GLOBAL_STYLE_DATA;
+            let guard = global_style_data.shared_lock.read();
             let rule = RwLock::<$rule_type>::as_arc(&rule);
-            rule.read().to_css(unsafe { result.as_mut().unwrap() }).unwrap();
+            rule.read().to_css(&guard, unsafe { result.as_mut().unwrap() }).unwrap();
         }
     }
 }

From 600152bd0049035d3c41dfe4aa381d0713d0127a Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Fri, 17 Mar 2017 01:02:55 +0100
Subject: [PATCH 06/17] Replace more RwLock<MediaList> with
 shared_lock::Locked<MediaList>

---
 components/script/dom/bindings/trace.rs   |  4 +--
 components/script/dom/cssconditionrule.rs |  4 +++
 components/script/dom/cssgroupingrule.rs  |  4 +++
 components/script/dom/cssmediarule.rs     |  7 ++--
 components/script/dom/medialist.rs        | 44 +++++++++++++++--------
 components/style/gecko/arc_types.rs       |  3 +-
 components/style/stylesheets.rs           | 13 ++++---
 ports/geckolib/glue.rs                    | 38 +++++++++++++-------
 8 files changed, 79 insertions(+), 38 deletions(-)

diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index b0828ab6d56..b0fabb5fd45 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -99,7 +99,7 @@ use style::keyframes::Keyframe;
 use style::media_queries::MediaList;
 use style::properties::PropertyDeclarationBlock;
 use style::selector_parser::{PseudoElement, Snapshot};
-use style::shared_lock::SharedRwLock as StyleSharedRwLock;
+use style::shared_lock::{SharedRwLock as StyleSharedRwLock, Locked as StyleLocked};
 use style::stylesheets::{CssRules, KeyframesRule, MediaRule, NamespaceRule, StyleRule, ImportRule};
 use style::stylesheets::SupportsRule;
 use style::values::specified::Length;
@@ -574,7 +574,7 @@ unsafe impl JSTraceable for RwLock<SharedRt> {
     }
 }
 
-unsafe impl JSTraceable for RwLock<MediaList> {
+unsafe impl JSTraceable for StyleLocked<MediaList> {
     unsafe fn trace(&self, _trc: *mut JSTracer) {
         // Do nothing.
     }
diff --git a/components/script/dom/cssconditionrule.rs b/components/script/dom/cssconditionrule.rs
index 42fca721759..44d10c21dd3 100644
--- a/components/script/dom/cssconditionrule.rs
+++ b/components/script/dom/cssconditionrule.rs
@@ -28,6 +28,10 @@ impl CSSConditionRule {
         }
     }
 
+    pub fn parent_stylesheet(&self) -> &CSSStyleSheet {
+        self.cssgroupingrule.parent_stylesheet()
+    }
+
     pub fn shared_lock(&self) -> &SharedRwLock {
         self.cssgroupingrule.shared_lock()
     }
diff --git a/components/script/dom/cssgroupingrule.rs b/components/script/dom/cssgroupingrule.rs
index 29f6bc361a2..7204b8447f9 100644
--- a/components/script/dom/cssgroupingrule.rs
+++ b/components/script/dom/cssgroupingrule.rs
@@ -42,6 +42,10 @@ impl CSSGroupingRule {
                                                   RulesSource::Rules(self.rules.clone())))
     }
 
+    pub fn parent_stylesheet(&self) -> &CSSStyleSheet {
+        self.cssrule.parent_stylesheet()
+    }
+
     pub fn shared_lock(&self) -> &SharedRwLock {
         self.cssrule.shared_lock()
     }
diff --git a/components/script/dom/cssmediarule.rs b/components/script/dom/cssmediarule.rs
index 9242ee01bb7..1d1f0846a51 100644
--- a/components/script/dom/cssmediarule.rs
+++ b/components/script/dom/cssmediarule.rs
@@ -50,22 +50,25 @@ impl CSSMediaRule {
 
     fn medialist(&self) -> Root<MediaList> {
         self.medialist.or_init(|| MediaList::new(self.global().as_window(),
+                                                 self.cssconditionrule.parent_stylesheet(),
                                                  self.mediarule.read().media_queries.clone()))
     }
 
     /// https://drafts.csswg.org/css-conditional-3/#the-cssmediarule-interface
     pub fn get_condition_text(&self) -> DOMString {
+        let guard = self.cssconditionrule.shared_lock().read();
         let rule = self.mediarule.read();
-        let list = rule.media_queries.read();
+        let list = rule.media_queries.read_with(&guard);
         list.to_css_string().into()
     }
 
     /// https://drafts.csswg.org/css-conditional-3/#the-cssmediarule-interface
     pub fn set_condition_text(&self, text: DOMString) {
+        let mut guard = self.cssconditionrule.shared_lock().write();
         let mut input = Parser::new(&text);
         let new_medialist = parse_media_query_list(&mut input);
         let rule = self.mediarule.read();
-        let mut list = rule.media_queries.write();
+        let mut list = rule.media_queries.write_with(&mut guard);
         *list = new_medialist;
     }
 }
diff --git a/components/script/dom/medialist.rs b/components/script/dom/medialist.rs
index 806946f6356..0020f7f3a08 100644
--- a/components/script/dom/medialist.rs
+++ b/components/script/dom/medialist.rs
@@ -6,13 +6,14 @@ use core::default::Default;
 use cssparser::Parser;
 use dom::bindings::codegen::Bindings::MediaListBinding;
 use dom::bindings::codegen::Bindings::MediaListBinding::MediaListMethods;
-use dom::bindings::js::Root;
+use dom::bindings::js::{JS, Root};
 use dom::bindings::reflector::{Reflector, reflect_dom_object};
 use dom::bindings::str::DOMString;
+use dom::cssstylesheet::CSSStyleSheet;
 use dom::window::Window;
 use dom_struct::dom_struct;
-use parking_lot::RwLock;
 use std::sync::Arc;
+use style::shared_lock::{SharedRwLock, Locked};
 use style::media_queries::{MediaQuery, parse_media_query_list};
 use style::media_queries::MediaList as StyleMediaList;
 use style_traits::ToCss;
@@ -20,38 +21,47 @@ use style_traits::ToCss;
 #[dom_struct]
 pub struct MediaList {
     reflector_: Reflector,
+    parent_stylesheet: JS<CSSStyleSheet>,
     #[ignore_heap_size_of = "Arc"]
-    media_queries: Arc<RwLock<StyleMediaList>>,
+    media_queries: Arc<Locked<StyleMediaList>>,
 }
 
 impl MediaList {
     #[allow(unrooted_must_root)]
-    pub fn new_inherited(media_queries: Arc<RwLock<StyleMediaList>>) -> MediaList {
+    pub fn new_inherited(parent_stylesheet: &CSSStyleSheet,
+                         media_queries: Arc<Locked<StyleMediaList>>) -> MediaList {
         MediaList {
+            parent_stylesheet: JS::from_ref(parent_stylesheet),
             reflector_: Reflector::new(),
             media_queries: media_queries,
         }
     }
 
     #[allow(unrooted_must_root)]
-    pub fn new(window: &Window, media_queries: Arc<RwLock<StyleMediaList>>)
+    pub fn new(window: &Window, parent_stylesheet: &CSSStyleSheet,
+               media_queries: Arc<Locked<StyleMediaList>>)
         -> Root<MediaList> {
-        reflect_dom_object(box MediaList::new_inherited(media_queries),
+        reflect_dom_object(box MediaList::new_inherited(parent_stylesheet, media_queries),
                            window,
                            MediaListBinding::Wrap)
     }
 
+    fn shared_lock(&self) -> &SharedRwLock {
+        &self.parent_stylesheet.style_stylesheet().shared_lock
+    }
 }
 
 impl MediaListMethods for MediaList {
     // https://drafts.csswg.org/cssom/#dom-medialist-mediatext
     fn MediaText(&self) -> DOMString {
-        DOMString::from(self.media_queries.read().to_css_string())
+        let guard = self.shared_lock().read();
+        DOMString::from(self.media_queries.read_with(&guard).to_css_string())
     }
 
     // https://drafts.csswg.org/cssom/#dom-medialist-mediatext
     fn SetMediaText(&self, value: DOMString) {
-        let mut media_queries = self.media_queries.write();
+        let mut guard = self.shared_lock().write();
+        let mut media_queries = self.media_queries.write_with(&mut guard);
         // Step 2
         if value.is_empty() {
             // Step 1
@@ -65,13 +75,15 @@ impl MediaListMethods for MediaList {
 
     // https://drafts.csswg.org/cssom/#dom-medialist-length
     fn Length(&self) -> u32 {
-        self.media_queries.read().media_queries.len() as u32
+        let guard = self.shared_lock().read();
+        self.media_queries.read_with(&guard).media_queries.len() as u32
     }
 
     // https://drafts.csswg.org/cssom/#dom-medialist-item
     fn Item(&self, index: u32) -> Option<DOMString> {
-        self.media_queries.read().media_queries.get(index as usize)
-                                            .and_then(|query| {
+        let guard = self.shared_lock().read();
+        self.media_queries.read_with(&guard).media_queries
+        .get(index as usize).and_then(|query| {
             let mut s = String::new();
             query.to_css(&mut s).unwrap();
             Some(DOMString::from_string(s))
@@ -94,13 +106,14 @@ impl MediaListMethods for MediaList {
         }
         // Step 3
         let m_serialized = m.clone().unwrap().to_css_string();
-        let any = self.media_queries.read().media_queries.iter()
-                                    .any(|q| m_serialized == q.to_css_string());
+        let mut guard = self.shared_lock().write();
+        let mq = self.media_queries.write_with(&mut guard);
+        let any = mq.media_queries.iter().any(|q| m_serialized == q.to_css_string());
         if any {
             return;
         }
         // Step 4
-        self.media_queries.write().media_queries.push(m.unwrap());
+        mq.media_queries.push(m.unwrap());
     }
 
     // https://drafts.csswg.org/cssom/#dom-medialist-deletemedium
@@ -114,7 +127,8 @@ impl MediaListMethods for MediaList {
         }
         // Step 3
         let m_serialized = m.unwrap().to_css_string();
-        let mut media_list = self.media_queries.write();
+        let mut guard = self.shared_lock().write();
+        let mut media_list = self.media_queries.write_with(&mut guard);
         let new_vec = media_list.media_queries.drain(..)
                                 .filter(|q| m_serialized != q.to_css_string())
                                 .collect();
diff --git a/components/style/gecko/arc_types.rs b/components/style/gecko/arc_types.rs
index d822857a9e6..daf0454c81e 100644
--- a/components/style/gecko/arc_types.rs
+++ b/components/style/gecko/arc_types.rs
@@ -17,6 +17,7 @@ use media_queries::MediaList;
 use parking_lot::RwLock;
 use properties::{ComputedValues, PropertyDeclarationBlock};
 use properties::animated_properties::{AnimationValue, AnimationValueMap};
+use shared_lock::Locked;
 use stylesheets::{CssRules, Stylesheet, StyleRule, ImportRule, MediaRule, NamespaceRule};
 
 macro_rules! impl_arc_ffi {
@@ -62,7 +63,7 @@ impl_arc_ffi!(AnimationValue => RawServoAnimationValue
 impl_arc_ffi!(RwLock<AnimationValueMap> => RawServoAnimationValueMap
               [Servo_AnimationValueMap_AddRef, Servo_AnimationValueMap_Release]);
 
-impl_arc_ffi!(RwLock<MediaList> => RawServoMediaList
+impl_arc_ffi!(Locked<MediaList> => RawServoMediaList
               [Servo_MediaList_AddRef, Servo_MediaList_Release]);
 
 impl_arc_ffi!(RwLock<MediaRule> => RawServoMediaRule
diff --git a/components/style/stylesheets.rs b/components/style/stylesheets.rs
index df6a9641f0d..3f3d78c1e16 100644
--- a/components/style/stylesheets.rs
+++ b/components/style/stylesheets.rs
@@ -316,7 +316,7 @@ impl CssRule {
             }
             CssRule::Media(ref lock) => {
                 let media_rule = lock.read();
-                let mq = media_rule.media_queries.read();
+                let mq = media_rule.media_queries.read_with(guard);
                 let rules = &media_rule.rules.read().0;
                 f(rules, Some(&mq))
             }
@@ -477,7 +477,7 @@ impl ToCssWithGuard for KeyframesRule {
 #[allow(missing_docs)]
 #[derive(Debug)]
 pub struct MediaRule {
-    pub media_queries: Arc<RwLock<MediaList>>,
+    pub media_queries: Arc<Locked<MediaList>>,
     pub rules: Arc<RwLock<CssRules>>,
 }
 
@@ -487,7 +487,7 @@ impl ToCssWithGuard for MediaRule {
     fn to_css<W>(&self, guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
     where W: fmt::Write {
         try!(dest.write_str("@media "));
-        try!(self.media_queries.read().to_css(dest));
+        try!(self.media_queries.read_with(guard).to_css(dest));
         try!(dest.write_str(" {"));
         for rule in self.rules.read().0.iter() {
             try!(dest.write_str(" "));
@@ -753,6 +753,7 @@ impl<'b> TopLevelRuleParser<'b> {
     fn nested<'a: 'b>(&'a self) -> NestedRuleParser<'a, 'b> {
         NestedRuleParser {
             stylesheet_origin: self.stylesheet_origin,
+            shared_lock: self.shared_lock,
             context: &self.context,
             namespaces: self.namespaces,
         }
@@ -774,7 +775,7 @@ enum AtRulePrelude {
     /// A @font-face rule prelude.
     FontFace,
     /// A @media rule prelude, with its media queries.
-    Media(Arc<RwLock<MediaList>>),
+    Media(Arc<Locked<MediaList>>),
     /// An @supports rule, with its conditional
     Supports(SupportsCondition),
     /// A @viewport rule prelude.
@@ -900,6 +901,7 @@ impl<'a> QualifiedRuleParser for TopLevelRuleParser<'a> {
 #[derive(Clone)]  // shallow, relatively cheap .clone
 struct NestedRuleParser<'a, 'b: 'a> {
     stylesheet_origin: Origin,
+    shared_lock: &'a SharedRwLock,
     context: &'a ParserContext<'b>,
     namespaces: &'b Namespaces,
 }
@@ -931,7 +933,8 @@ impl<'a, 'b> AtRuleParser for NestedRuleParser<'a, 'b> {
         match_ignore_ascii_case! { name,
             "media" => {
                 let media_queries = parse_media_query_list(input);
-                Ok(AtRuleType::WithBlock(AtRulePrelude::Media(Arc::new(RwLock::new(media_queries)))))
+                let arc = Arc::new(self.shared_lock.wrap(media_queries));
+                Ok(AtRuleType::WithBlock(AtRulePrelude::Media(arc)))
             },
             "supports" => {
                 let cond = SupportsCondition::parse(input)?;
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index cdc0a530f09..e0335ee0005 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -76,7 +76,7 @@ use style::properties::parse_one_declaration;
 use style::restyle_hints::{self, RestyleHint};
 use style::selector_parser::PseudoElementCascadeType;
 use style::sequential;
-use style::shared_lock::{SharedRwLock, ToCssWithGuard};
+use style::shared_lock::{SharedRwLock, ToCssWithGuard, Locked};
 use style::string_cache::Atom;
 use style::stylesheets::{CssRule, CssRules, ImportRule, MediaRule, NamespaceRule};
 use style::stylesheets::{Origin, Stylesheet, StyleRule};
@@ -964,29 +964,37 @@ pub extern "C" fn Servo_DeclarationBlock_RemovePropertyById(declarations: RawSer
 
 #[no_mangle]
 pub extern "C" fn Servo_MediaList_GetText(list: RawServoMediaListBorrowed, result: *mut nsAString) {
-    let list = RwLock::<MediaList>::as_arc(&list);
-    list.read().to_css(unsafe { result.as_mut().unwrap() }).unwrap();
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let list = Locked::<MediaList>::as_arc(&list);
+    list.read_with(&guard).to_css(unsafe { result.as_mut().unwrap() }).unwrap();
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_MediaList_SetText(list: RawServoMediaListBorrowed, text: *const nsACString) {
-    let list = RwLock::<MediaList>::as_arc(&list);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    let list = Locked::<MediaList>::as_arc(&list);
     let text = unsafe { text.as_ref().unwrap().as_str_unchecked() };
     let mut parser = Parser::new(&text);
-    *list.write() = parse_media_query_list(&mut parser);
+    *list.write_with(&mut guard) = parse_media_query_list(&mut parser);
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_MediaList_GetLength(list: RawServoMediaListBorrowed) -> u32 {
-    let list = RwLock::<MediaList>::as_arc(&list);
-    list.read().media_queries.len() as u32
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let list = Locked::<MediaList>::as_arc(&list);
+    list.read_with(&guard).media_queries.len() as u32
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_MediaList_GetMediumAt(list: RawServoMediaListBorrowed, index: u32,
                                               result: *mut nsAString) -> bool {
-    let list = RwLock::<MediaList>::as_arc(&list);
-    if let Some(media_query) = list.read().media_queries.get(index as usize) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let list = Locked::<MediaList>::as_arc(&list);
+    if let Some(media_query) = list.read_with(&guard).media_queries.get(index as usize) {
         media_query.to_css(unsafe { result.as_mut().unwrap() }).unwrap();
         true
     } else {
@@ -997,17 +1005,21 @@ pub extern "C" fn Servo_MediaList_GetMediumAt(list: RawServoMediaListBorrowed, i
 #[no_mangle]
 pub extern "C" fn Servo_MediaList_AppendMedium(list: RawServoMediaListBorrowed,
                                                new_medium: *const nsACString) {
-    let list = RwLock::<MediaList>::as_arc(&list);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    let list = Locked::<MediaList>::as_arc(&list);
     let new_medium = unsafe { new_medium.as_ref().unwrap().as_str_unchecked() };
-    list.write().append_medium(new_medium);
+    list.write_with(&mut guard).append_medium(new_medium);
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_MediaList_DeleteMedium(list: RawServoMediaListBorrowed,
                                                old_medium: *const nsACString) -> bool {
-    let list = RwLock::<MediaList>::as_arc(&list);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    let list = Locked::<MediaList>::as_arc(&list);
     let old_medium = unsafe { old_medium.as_ref().unwrap().as_str_unchecked() };
-    list.write().delete_medium(old_medium)
+    list.write_with(&mut guard).delete_medium(old_medium)
 }
 
 macro_rules! get_longhand_from_id {

From b213daaa8818ff59557973c01c7d2612e9389abc Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Fri, 17 Mar 2017 01:16:49 +0100
Subject: [PATCH 07/17] Tidy

---
 components/script/dom/cssfontfacerule.rs | 2 +-
 components/script/dom/medialist.rs       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/components/script/dom/cssfontfacerule.rs b/components/script/dom/cssfontfacerule.rs
index 4556f90a56c..05b665a9975 100644
--- a/components/script/dom/cssfontfacerule.rs
+++ b/components/script/dom/cssfontfacerule.rs
@@ -12,8 +12,8 @@ use dom::window::Window;
 use dom_struct::dom_struct;
 use parking_lot::RwLock;
 use std::sync::Arc;
-use style::shared_lock::ToCssWithGuard;
 use style::font_face::FontFaceRule;
+use style::shared_lock::ToCssWithGuard;
 
 #[dom_struct]
 pub struct CSSFontFaceRule {
diff --git a/components/script/dom/medialist.rs b/components/script/dom/medialist.rs
index 0020f7f3a08..b403200983e 100644
--- a/components/script/dom/medialist.rs
+++ b/components/script/dom/medialist.rs
@@ -13,9 +13,9 @@ use dom::cssstylesheet::CSSStyleSheet;
 use dom::window::Window;
 use dom_struct::dom_struct;
 use std::sync::Arc;
-use style::shared_lock::{SharedRwLock, Locked};
 use style::media_queries::{MediaQuery, parse_media_query_list};
 use style::media_queries::MediaList as StyleMediaList;
+use style::shared_lock::{SharedRwLock, Locked};
 use style_traits::ToCss;
 
 #[dom_struct]

From f35b4e27b3e0b748e10662cfb6f18873258483b7 Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Fri, 17 Mar 2017 11:01:13 +0100
Subject: [PATCH 08/17] Replace RwLock<CssRules> with Locked<CssRules>

---
 components/script/dom/bindings/trace.rs   |  2 +-
 components/script/dom/cssconditionrule.rs |  5 +--
 components/script/dom/cssgroupingrule.rs  |  7 ++-
 components/script/dom/cssrulelist.rs      | 16 ++++---
 components/script/dom/cssstylesheet.rs    |  5 +++
 components/script/dom/htmlmetaelement.rs  |  3 +-
 components/script/stylesheet_loader.rs    |  2 +
 components/style/encoding_support.rs      |  4 +-
 components/style/gecko/arc_types.rs       |  2 +-
 components/style/stylesheets.rs           | 52 +++++++++++++----------
 components/style/stylist.rs               |  2 +-
 ports/geckolib/glue.rs                    | 30 +++++++++----
 tests/unit/style/media_queries.rs         |  2 +-
 tests/unit/style/rule_tree/bench.rs       |  3 +-
 tests/unit/style/stylesheets.rs           |  2 +-
 15 files changed, 85 insertions(+), 52 deletions(-)

diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index b0fabb5fd45..122823f6f0d 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -508,7 +508,7 @@ unsafe impl JSTraceable for RwLock<FontFaceRule> {
     }
 }
 
-unsafe impl JSTraceable for RwLock<CssRules> {
+unsafe impl JSTraceable for StyleLocked<CssRules> {
     unsafe fn trace(&self, _trc: *mut JSTracer) {
         // Do nothing.
     }
diff --git a/components/script/dom/cssconditionrule.rs b/components/script/dom/cssconditionrule.rs
index 44d10c21dd3..8bf5dad6c93 100644
--- a/components/script/dom/cssconditionrule.rs
+++ b/components/script/dom/cssconditionrule.rs
@@ -10,9 +10,8 @@ use dom::cssmediarule::CSSMediaRule;
 use dom::cssstylesheet::CSSStyleSheet;
 use dom::csssupportsrule::CSSSupportsRule;
 use dom_struct::dom_struct;
-use parking_lot::RwLock;
 use std::sync::Arc;
-use style::shared_lock::SharedRwLock;
+use style::shared_lock::{SharedRwLock, Locked};
 use style::stylesheets::CssRules as StyleCssRules;
 
 #[dom_struct]
@@ -22,7 +21,7 @@ pub struct CSSConditionRule {
 
 impl CSSConditionRule {
     pub fn new_inherited(parent_stylesheet: &CSSStyleSheet,
-                         rules: Arc<RwLock<StyleCssRules>>) -> CSSConditionRule {
+                         rules: Arc<Locked<StyleCssRules>>) -> CSSConditionRule {
         CSSConditionRule {
             cssgroupingrule: CSSGroupingRule::new_inherited(parent_stylesheet, rules),
         }
diff --git a/components/script/dom/cssgroupingrule.rs b/components/script/dom/cssgroupingrule.rs
index 7204b8447f9..249aaccd42e 100644
--- a/components/script/dom/cssgroupingrule.rs
+++ b/components/script/dom/cssgroupingrule.rs
@@ -12,22 +12,21 @@ use dom::cssrule::CSSRule;
 use dom::cssrulelist::{CSSRuleList, RulesSource};
 use dom::cssstylesheet::CSSStyleSheet;
 use dom_struct::dom_struct;
-use parking_lot::RwLock;
 use std::sync::Arc;
-use style::shared_lock::SharedRwLock;
+use style::shared_lock::{SharedRwLock, Locked};
 use style::stylesheets::CssRules as StyleCssRules;
 
 #[dom_struct]
 pub struct CSSGroupingRule {
     cssrule: CSSRule,
     #[ignore_heap_size_of = "Arc"]
-    rules: Arc<RwLock<StyleCssRules>>,
+    rules: Arc<Locked<StyleCssRules>>,
     rulelist: MutNullableJS<CSSRuleList>,
 }
 
 impl CSSGroupingRule {
     pub fn new_inherited(parent_stylesheet: &CSSStyleSheet,
-                         rules: Arc<RwLock<StyleCssRules>>) -> CSSGroupingRule {
+                         rules: Arc<Locked<StyleCssRules>>) -> CSSGroupingRule {
         CSSGroupingRule {
             cssrule: CSSRule::new_inherited(parent_stylesheet),
             rules: rules,
diff --git a/components/script/dom/cssrulelist.rs b/components/script/dom/cssrulelist.rs
index 0b6351d237c..6321296c785 100644
--- a/components/script/dom/cssrulelist.rs
+++ b/components/script/dom/cssrulelist.rs
@@ -15,6 +15,7 @@ use dom::window::Window;
 use dom_struct::dom_struct;
 use parking_lot::RwLock;
 use std::sync::Arc;
+use style::shared_lock::Locked;
 use style::stylesheets::{CssRules, KeyframesRule, RulesMutateError};
 
 #[allow(unsafe_code)]
@@ -43,7 +44,7 @@ pub struct CSSRuleList {
 }
 
 pub enum RulesSource {
-    Rules(Arc<RwLock<CssRules>>),
+    Rules(Arc<Locked<CssRules>>),
     Keyframes(Arc<RwLock<KeyframesRule>>),
 }
 
@@ -52,7 +53,8 @@ impl CSSRuleList {
     pub fn new_inherited(parent_stylesheet: &CSSStyleSheet, rules: RulesSource) -> CSSRuleList {
         let dom_rules = match rules {
             RulesSource::Rules(ref rules) => {
-                rules.read().0.iter().map(|_| MutNullableJS::new(None)).collect()
+                let guard = parent_stylesheet.shared_lock().read();
+                rules.read_with(&guard).0.iter().map(|_| MutNullableJS::new(None)).collect()
             }
             RulesSource::Keyframes(ref rules) => {
                 rules.read().keyframes.iter().map(|_| MutNullableJS::new(None)).collect()
@@ -89,7 +91,9 @@ impl CSSRuleList {
         let index = idx as usize;
 
         let parent_stylesheet = self.parent_stylesheet.style_stylesheet();
-        let new_rule = css_rules.write().insert_rule(rule, parent_stylesheet, index, nested)?;
+        let mut guard = parent_stylesheet.shared_lock.write();
+        let new_rule = css_rules.write_with(&mut guard)
+            .insert_rule(rule, parent_stylesheet, index, nested)?;
 
         let parent_stylesheet = &*self.parent_stylesheet;
         let dom_rule = CSSRule::new_specific(&window, parent_stylesheet, new_rule);
@@ -103,7 +107,8 @@ impl CSSRuleList {
 
         match self.rules {
             RulesSource::Rules(ref css_rules) => {
-                css_rules.write().remove_rule(index)?;
+                let mut guard = self.parent_stylesheet.shared_lock().write();
+                css_rules.write_with(&mut guard).remove_rule(index)?;
                 let mut dom_rules = self.dom_rules.borrow_mut();
                 dom_rules[index].get().map(|r| r.detach());
                 dom_rules.remove(index);
@@ -133,9 +138,10 @@ impl CSSRuleList {
                 let parent_stylesheet = &self.parent_stylesheet;
                 match self.rules {
                     RulesSource::Rules(ref rules) => {
+                        let guard = parent_stylesheet.shared_lock().read();
                         CSSRule::new_specific(self.global().as_window(),
                                              parent_stylesheet,
-                                             rules.read().0[idx as usize].clone())
+                                             rules.read_with(&guard).0[idx as usize].clone())
                     }
                     RulesSource::Keyframes(ref rules) => {
                         Root::upcast(CSSKeyframeRule::new(self.global().as_window(),
diff --git a/components/script/dom/cssstylesheet.rs b/components/script/dom/cssstylesheet.rs
index f8397a732c2..ee097313c2e 100644
--- a/components/script/dom/cssstylesheet.rs
+++ b/components/script/dom/cssstylesheet.rs
@@ -16,6 +16,7 @@ use dom::window::Window;
 use dom_struct::dom_struct;
 use std::cell::Cell;
 use std::sync::Arc;
+use style::shared_lock::SharedRwLock;
 use style::stylesheets::Stylesheet as StyleStyleSheet;
 
 #[dom_struct]
@@ -72,6 +73,10 @@ impl CSSStyleSheet {
         }
     }
 
+    pub fn shared_lock(&self) -> &SharedRwLock {
+        &self.style_stylesheet.shared_lock
+    }
+
     pub fn style_stylesheet(&self) -> &StyleStyleSheet {
         &self.style_stylesheet
     }
diff --git a/components/script/dom/htmlmetaelement.rs b/components/script/dom/htmlmetaelement.rs
index 2f78e74d3b4..a564c6b2661 100644
--- a/components/script/dom/htmlmetaelement.rs
+++ b/components/script/dom/htmlmetaelement.rs
@@ -101,8 +101,9 @@ impl HTMLMetaElement {
                 if let Some(translated_rule) = ViewportRule::from_meta(&**content) {
                     let document = self.upcast::<Node>().owner_doc();
                     let shared_lock = document.style_shared_lock();
+                    let rule = CssRule::Viewport(Arc::new(RwLock::new(translated_rule)));
                     *self.stylesheet.borrow_mut() = Some(Arc::new(Stylesheet {
-                        rules: CssRules::new(vec![CssRule::Viewport(Arc::new(RwLock::new(translated_rule)))]),
+                        rules: CssRules::new(vec![rule], shared_lock),
                         origin: Origin::Author,
                         shared_lock: shared_lock.clone(),
                         base_url: window_from_node(self).get_url(),
diff --git a/components/script/stylesheet_loader.rs b/components/script/stylesheet_loader.rs
index 26dffa5fe56..79b90be7426 100644
--- a/components/script/stylesheet_loader.rs
+++ b/components/script/stylesheet_loader.rs
@@ -175,10 +175,12 @@ impl FetchResponseListener for StylesheetContext {
                 }
                 StylesheetContextSource::Import(ref import) => {
                     let import = import.read();
+                    let mut guard = document.style_shared_lock().write();
                     Stylesheet::update_from_bytes(&import.stylesheet,
                                                   &data,
                                                   protocol_encoding_label,
                                                   Some(environment_encoding),
+                                                  &mut guard,
                                                   Some(&loader),
                                                   win.css_error_reporter(),
                                                   ParserContextExtraData::default());
diff --git a/components/style/encoding_support.rs b/components/style/encoding_support.rs
index 141291c896e..e485dc13cf0 100644
--- a/components/style/encoding_support.rs
+++ b/components/style/encoding_support.rs
@@ -12,7 +12,7 @@ use media_queries::MediaList;
 use parser::ParserContextExtraData;
 use self::encoding::{EncodingRef, DecoderTrap};
 use servo_url::ServoUrl;
-use shared_lock::SharedRwLock;
+use shared_lock::{SharedRwLock, SharedRwLockWriteGuard};
 use std::str;
 use stylesheets::{Stylesheet, StylesheetLoader, Origin};
 
@@ -78,6 +78,7 @@ impl Stylesheet {
                              bytes: &[u8],
                              protocol_encoding_label: Option<&str>,
                              environment_encoding: Option<EncodingRef>,
+                             guard: &mut SharedRwLockWriteGuard,
                              stylesheet_loader: Option<&StylesheetLoader>,
                              error_reporter: &ParseErrorReporter,
                              extra_data: ParserContextExtraData) {
@@ -85,6 +86,7 @@ impl Stylesheet {
             bytes, protocol_encoding_label, environment_encoding);
         Self::update_from_str(existing,
                               &string,
+                              guard,
                               stylesheet_loader,
                               error_reporter,
                               extra_data)
diff --git a/components/style/gecko/arc_types.rs b/components/style/gecko/arc_types.rs
index daf0454c81e..798af00906e 100644
--- a/components/style/gecko/arc_types.rs
+++ b/components/style/gecko/arc_types.rs
@@ -39,7 +39,7 @@ macro_rules! impl_arc_ffi {
     }
 }
 
-impl_arc_ffi!(RwLock<CssRules> => ServoCssRules
+impl_arc_ffi!(Locked<CssRules> => ServoCssRules
               [Servo_CssRules_AddRef, Servo_CssRules_Release]);
 
 impl_arc_ffi!(Stylesheet => RawServoStyleSheet
diff --git a/components/style/stylesheets.rs b/components/style/stylesheets.rs
index 3f3d78c1e16..07dc2632b2d 100644
--- a/components/style/stylesheets.rs
+++ b/components/style/stylesheets.rs
@@ -21,7 +21,8 @@ use selector_parser::{SelectorImpl, SelectorParser};
 use selectors::parser::SelectorList;
 use servo_config::prefs::PREFS;
 use servo_url::ServoUrl;
-use shared_lock::{SharedRwLock, Locked, SharedRwLockReadGuard, ToCssWithGuard};
+use shared_lock::{SharedRwLock, Locked, ToCssWithGuard};
+use shared_lock::{SharedRwLockReadGuard, SharedRwLockWriteGuard};
 use std::cell::Cell;
 use std::fmt;
 use std::sync::Arc;
@@ -87,8 +88,8 @@ impl From<SingleRuleParseError> for RulesMutateError {
 
 impl CssRules {
     #[allow(missing_docs)]
-    pub fn new(rules: Vec<CssRule>) -> Arc<RwLock<CssRules>> {
-        Arc::new(RwLock::new(CssRules(rules)))
+    pub fn new(rules: Vec<CssRule>, shared_lock: &SharedRwLock) -> Arc<Locked<CssRules>> {
+        Arc::new(shared_lock.wrap(CssRules(rules)))
     }
 
     fn only_ns_or_import(&self) -> bool {
@@ -174,7 +175,7 @@ impl CssRules {
 pub struct Stylesheet {
     /// List of rules in the order they were found (important for
     /// cascading order)
-    pub rules: Arc<RwLock<CssRules>>,
+    pub rules: Arc<Locked<CssRules>>,
     /// List of media associated with the Stylesheet.
     pub media: Arc<Locked<MediaList>>,
     /// The origin of this stylesheet.
@@ -302,7 +303,7 @@ impl CssRule {
             CssRule::Import(ref lock) => {
                 let rule = lock.read();
                 let media = rule.stylesheet.media.read_with(guard);
-                let rules = rule.stylesheet.rules.read();
+                let rules = rule.stylesheet.rules.read_with(guard);
                 // FIXME(emilio): Include the nested rules if the stylesheet is
                 // loaded.
                 f(&rules.0, Some(&media))
@@ -317,14 +318,14 @@ impl CssRule {
             CssRule::Media(ref lock) => {
                 let media_rule = lock.read();
                 let mq = media_rule.media_queries.read_with(guard);
-                let rules = &media_rule.rules.read().0;
+                let rules = &media_rule.rules.read_with(guard).0;
                 f(rules, Some(&mq))
             }
             CssRule::Supports(ref lock) => {
                 let supports_rule = lock.read();
                 let enabled = supports_rule.enabled;
                 if enabled {
-                    let rules = &supports_rule.rules.read().0;
+                    let rules = &supports_rule.rules.read_with(guard).0;
                     f(rules, None)
                 } else {
                     f(&[], None)
@@ -478,7 +479,7 @@ impl ToCssWithGuard for KeyframesRule {
 #[derive(Debug)]
 pub struct MediaRule {
     pub media_queries: Arc<Locked<MediaList>>,
-    pub rules: Arc<RwLock<CssRules>>,
+    pub rules: Arc<Locked<CssRules>>,
 }
 
 impl ToCssWithGuard for MediaRule {
@@ -489,7 +490,7 @@ impl ToCssWithGuard for MediaRule {
         try!(dest.write_str("@media "));
         try!(self.media_queries.read_with(guard).to_css(dest));
         try!(dest.write_str(" {"));
-        for rule in self.rules.read().0.iter() {
+        for rule in self.rules.read_with(guard).0.iter() {
             try!(dest.write_str(" "));
             try!(rule.to_css(guard, dest));
         }
@@ -504,7 +505,7 @@ pub struct SupportsRule {
     /// The parsed condition
     pub condition: SupportsCondition,
     /// Child rules
-    pub rules: Arc<RwLock<CssRules>>,
+    pub rules: Arc<Locked<CssRules>>,
     /// The result of evaluating the condition
     pub enabled: bool,
 }
@@ -515,7 +516,7 @@ impl ToCssWithGuard for SupportsRule {
         try!(dest.write_str("@supports "));
         try!(self.condition.to_css(dest));
         try!(dest.write_str(" {"));
-        for rule in self.rules.read().0.iter() {
+        for rule in self.rules.read_with(guard).0.iter() {
             try!(dest.write_str(" "));
             try!(rule.to_css(guard, dest));
         }
@@ -555,10 +556,11 @@ impl Stylesheet {
     /// Updates an empty stylesheet from a given string of text.
     pub fn update_from_str(existing: &Stylesheet,
                            css: &str,
+                           guard: &mut SharedRwLockWriteGuard,
                            stylesheet_loader: Option<&StylesheetLoader>,
                            error_reporter: &ParseErrorReporter,
                            extra_data: ParserContextExtraData) {
-        let mut rules = existing.rules.write();
+        let mut rules = existing.rules.write_with(guard);
         let mut namespaces = existing.namespaces.write();
 
         assert!(rules.is_empty());
@@ -613,18 +615,22 @@ impl Stylesheet {
             origin: origin,
             base_url: base_url,
             namespaces: RwLock::new(Namespaces::default()),
-            rules: CssRules::new(vec![]),
+            rules: CssRules::new(Vec::new(), &shared_lock),
             media: Arc::new(shared_lock.wrap(media)),
-            shared_lock: shared_lock.clone(),
+            shared_lock: shared_lock,
             dirty_on_viewport_size_change: AtomicBool::new(false),
             disabled: AtomicBool::new(false),
         };
 
-        Self::update_from_str(&s,
-                              css,
-                              stylesheet_loader,
-                              error_reporter,
-                              extra_data);
+        {
+            let mut guard = s.shared_lock.write();
+            Self::update_from_str(&s,
+                                  css,
+                                  &mut guard,
+                                  stylesheet_loader,
+                                  error_reporter,
+                                  extra_data);
+        }
 
         s
     }
@@ -666,7 +672,7 @@ impl Stylesheet {
     #[inline]
     pub fn effective_rules<F>(&self, device: &Device, guard: &SharedRwLockReadGuard, mut f: F)
     where F: FnMut(&CssRule) {
-        effective_rules(&self.rules.read().0, device, guard, &mut f);
+        effective_rules(&self.rules.read_with(guard).0, device, guard, &mut f);
     }
 
     /// Returns whether the stylesheet has been explicitly disabled through the
@@ -809,7 +815,7 @@ impl<'a> AtRuleParser for TopLevelRuleParser<'a> {
                         ImportRule {
                             url: url,
                             stylesheet: Arc::new(Stylesheet {
-                                rules: Arc::new(RwLock::new(CssRules(vec![]))),
+                                rules: CssRules::new(Vec::new(), self.shared_lock),
                                 media: media,
                                 shared_lock: self.shared_lock.clone(),
                                 origin: self.context.stylesheet_origin,
@@ -907,7 +913,7 @@ struct NestedRuleParser<'a, 'b: 'a> {
 }
 
 impl<'a, 'b> NestedRuleParser<'a, 'b> {
-    fn parse_nested_rules(&self, input: &mut Parser) -> Arc<RwLock<CssRules>> {
+    fn parse_nested_rules(&self, input: &mut Parser) -> Arc<Locked<CssRules>> {
         let mut iter = RuleListParser::new_for_nested_rule(input, self.clone());
         let mut rules = Vec::new();
         while let Some(result) = iter.next() {
@@ -920,7 +926,7 @@ impl<'a, 'b> NestedRuleParser<'a, 'b> {
                 }
             }
         }
-        CssRules::new(rules)
+        CssRules::new(rules, self.shared_lock)
     }
 }
 
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index 0ff9d20d883..73684a4b8fd 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -502,7 +502,7 @@ impl Stylist {
                 return true
             }
 
-            mq_eval_changed(guard, &stylesheet.rules.read().0, &self.device, &device)
+            mq_eval_changed(guard, &stylesheet.rules.read_with(guard).0, &self.device, &device)
         });
 
         self.device = Arc::new(device);
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index e0335ee0005..e260f365fa5 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -402,6 +402,8 @@ pub extern "C" fn Servo_StyleSheet_ClearAndUpdate(stylesheet: RawServoStyleSheet
                                                   referrer: *mut ThreadSafeURIHolder,
                                                   principal: *mut ThreadSafePrincipalHolder)
 {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
     let input = unsafe { data.as_ref().unwrap().as_str_unchecked() };
     let extra_data = unsafe { ParserContextExtraData {
         base: Some(GeckoArcURI::new(base)),
@@ -422,9 +424,9 @@ pub extern "C" fn Servo_StyleSheet_ClearAndUpdate(stylesheet: RawServoStyleSheet
     };
 
     let sheet = Stylesheet::as_arc(&stylesheet);
-    sheet.rules.write().0.clear();
+    sheet.rules.write_with(&mut guard).0.clear();
 
-    Stylesheet::update_from_str(&sheet, input, loader,
+    Stylesheet::update_from_str(&sheet, input, &mut guard, loader,
                                 &StdoutErrorReporter, extra_data);
 }
 
@@ -510,7 +512,9 @@ pub extern "C" fn Servo_StyleSet_NoteStyleSheetsChanged(raw_data: RawServoStyleS
 
 #[no_mangle]
 pub extern "C" fn Servo_StyleSheet_HasRules(raw_sheet: RawServoStyleSheetBorrowed) -> bool {
-    !Stylesheet::as_arc(&raw_sheet).rules.read().0.is_empty()
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    !Stylesheet::as_arc(&raw_sheet).rules.read_with(&guard).0.is_empty()
 }
 
 #[no_mangle]
@@ -521,7 +525,9 @@ pub extern "C" fn Servo_StyleSheet_GetRules(sheet: RawServoStyleSheetBorrowed) -
 #[no_mangle]
 pub extern "C" fn Servo_CssRules_ListTypes(rules: ServoCssRulesBorrowed,
                                            result: nsTArrayBorrowed_uintptr_t) {
-    let rules = RwLock::<CssRules>::as_arc(&rules).read();
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let rules = Locked::<CssRules>::as_arc(&rules).read_with(&guard);
     let iter = rules.0.iter().map(|rule| rule.rule_type() as usize);
     let (size, upper) = iter.size_hint();
     debug_assert_eq!(size, upper.unwrap());
@@ -533,10 +539,12 @@ pub extern "C" fn Servo_CssRules_ListTypes(rules: ServoCssRulesBorrowed,
 pub extern "C" fn Servo_CssRules_InsertRule(rules: ServoCssRulesBorrowed, sheet: RawServoStyleSheetBorrowed,
                                             rule: *const nsACString, index: u32, nested: bool,
                                             rule_type: *mut u16) -> nsresult {
-    let rules = RwLock::<CssRules>::as_arc(&rules);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    let rules = Locked::<CssRules>::as_arc(&rules);
     let sheet = Stylesheet::as_arc(&sheet);
     let rule = unsafe { rule.as_ref().unwrap().as_str_unchecked() };
-    match rules.write().insert_rule(rule, sheet, index as usize, nested) {
+    match rules.write_with(&mut guard).insert_rule(rule, sheet, index as usize, nested) {
         Ok(new_rule) => {
             *unsafe { rule_type.as_mut().unwrap() } = new_rule.rule_type() as u16;
             nsresult::NS_OK
@@ -547,8 +555,10 @@ pub extern "C" fn Servo_CssRules_InsertRule(rules: ServoCssRulesBorrowed, sheet:
 
 #[no_mangle]
 pub extern "C" fn Servo_CssRules_DeleteRule(rules: ServoCssRulesBorrowed, index: u32) -> nsresult {
-    let rules = RwLock::<CssRules>::as_arc(&rules);
-    match rules.write().remove_rule(index as usize) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    let rules = Locked::<CssRules>::as_arc(&rules);
+    match rules.write_with(&mut guard).remove_rule(index as usize) {
         Ok(_) => nsresult::NS_OK,
         Err(err) => err.into()
     }
@@ -562,7 +572,9 @@ macro_rules! impl_basic_rule_funcs {
     } => {
         #[no_mangle]
         pub extern "C" fn $getter(rules: ServoCssRulesBorrowed, index: u32) -> Strong<$raw_type> {
-            let rules = RwLock::<CssRules>::as_arc(&rules).read();
+            let global_style_data = &*GLOBAL_STYLE_DATA;
+            let guard = global_style_data.shared_lock.read();
+            let rules = Locked::<CssRules>::as_arc(&rules).read_with(&guard);
             match rules.0[index as usize] {
                 CssRule::$name(ref rule) => rule.clone().into_strong(),
                 _ => {
diff --git a/tests/unit/style/media_queries.rs b/tests/unit/style/media_queries.rs
index 652d68ce953..3d2f2809a63 100644
--- a/tests/unit/style/media_queries.rs
+++ b/tests/unit/style/media_queries.rs
@@ -35,7 +35,7 @@ fn test_media_rule<F>(css: &str, callback: F)
         ParserContextExtraData::default());
     let mut rule_count = 0;
     let guard = stylesheet.shared_lock.read();
-    media_queries(&guard, &stylesheet.rules.read().0, &mut |mq| {
+    media_queries(&guard, &stylesheet.rules.read_with(&guard).0, &mut |mq| {
         rule_count += 1;
         callback(mq, css);
     });
diff --git a/tests/unit/style/rule_tree/bench.rs b/tests/unit/style/rule_tree/bench.rs
index 623a534159a..aeac93912aa 100644
--- a/tests/unit/style/rule_tree/bench.rs
+++ b/tests/unit/style/rule_tree/bench.rs
@@ -49,7 +49,8 @@ fn parse_rules(css: &str) -> Vec<(StyleSource, CascadeLevel)> {
                                  None,
                                  &ErrorringErrorReporter,
                                  ParserContextExtraData {});
-    let rules = s.rules.read();
+    let guard = s.shared_lock.read();
+    let rules = s.rules.read_with(&guard);
     rules.0.iter().filter_map(|rule| {
         match *rule {
             CssRule::Style(ref style_rule) => Some(style_rule),
diff --git a/tests/unit/style/stylesheets.rs b/tests/unit/style/stylesheets.rs
index 590e93185f4..00cefe23ce9 100644
--- a/tests/unit/style/stylesheets.rs
+++ b/tests/unit/style/stylesheets.rs
@@ -263,7 +263,7 @@ fn test_parse_stylesheet() {
                 ]
             })))
 
-        ]),
+        ], &stylesheet.shared_lock),
     };
 
     assert_eq!(format!("{:#?}", stylesheet), format!("{:#?}", expected));

From adb97d4cbefde92b3645619d826ce175a787a069 Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Fri, 17 Mar 2017 16:46:22 +0100
Subject: [PATCH 09/17] Wrap most CSS rules in Locked<_> instead of RwLock<_>

---
 components/script/dom/bindings/trace.rs   | 14 ++---
 components/script/dom/cssfontfacerule.rs  | 11 ++--
 components/script/dom/cssimportrule.rs    | 11 ++--
 components/script/dom/csskeyframesrule.rs | 23 ++++----
 components/script/dom/cssmediarule.rs     | 39 ++++++++-----
 components/script/dom/cssnamespacerule.rs | 17 +++---
 components/script/dom/cssrulelist.rs      | 15 +++--
 components/script/dom/csssupportsrule.rs  | 20 ++++---
 components/script/dom/cssviewportrule.rs  | 11 ++--
 components/script/dom/htmlmetaelement.rs  |  3 +-
 components/script/stylesheet_loader.rs    | 26 ++++++---
 components/style/gecko/arc_types.rs       | 17 +++++-
 components/style/stylesheets.rs           | 70 +++++++++++++----------
 components/style/stylist.rs               |  4 +-
 ports/geckolib/glue.rs                    | 42 +++++++++-----
 ports/geckolib/stylesheet_loader.rs       |  6 +-
 tests/unit/style/stylesheets.rs           |  4 +-
 17 files changed, 194 insertions(+), 139 deletions(-)

diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index 122823f6f0d..efa1a5646f2 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -502,7 +502,7 @@ unsafe impl JSTraceable for Mutex<Option<SharedRt>> {
     }
 }
 
-unsafe impl JSTraceable for RwLock<FontFaceRule> {
+unsafe impl JSTraceable for StyleLocked<FontFaceRule> {
     unsafe fn trace(&self, _trc: *mut JSTracer) {
         // Do nothing.
     }
@@ -520,31 +520,31 @@ unsafe impl JSTraceable for RwLock<Keyframe> {
     }
 }
 
-unsafe impl JSTraceable for RwLock<KeyframesRule> {
+unsafe impl JSTraceable for StyleLocked<KeyframesRule> {
     unsafe fn trace(&self, _trc: *mut JSTracer) {
         // Do nothing.
     }
 }
 
-unsafe impl JSTraceable for RwLock<ImportRule> {
+unsafe impl JSTraceable for StyleLocked<ImportRule> {
     unsafe fn trace(&self, _trc: *mut JSTracer) {
         // Do nothing.
     }
 }
 
-unsafe impl JSTraceable for RwLock<SupportsRule> {
+unsafe impl JSTraceable for StyleLocked<SupportsRule> {
     unsafe fn trace(&self, _trc: *mut JSTracer) {
         // Do nothing.
     }
 }
 
-unsafe impl JSTraceable for RwLock<MediaRule> {
+unsafe impl JSTraceable for StyleLocked<MediaRule> {
     unsafe fn trace(&self, _trc: *mut JSTracer) {
         // Do nothing.
     }
 }
 
-unsafe impl JSTraceable for RwLock<NamespaceRule> {
+unsafe impl JSTraceable for StyleLocked<NamespaceRule> {
     unsafe fn trace(&self, _trc: *mut JSTracer) {
         // Do nothing.
     }
@@ -556,7 +556,7 @@ unsafe impl JSTraceable for RwLock<StyleRule> {
     }
 }
 
-unsafe impl JSTraceable for RwLock<ViewportRule> {
+unsafe impl JSTraceable for StyleLocked<ViewportRule> {
     unsafe fn trace(&self, _trc: *mut JSTracer) {
         // Do nothing.
     }
diff --git a/components/script/dom/cssfontfacerule.rs b/components/script/dom/cssfontfacerule.rs
index 05b665a9975..184f6784afa 100644
--- a/components/script/dom/cssfontfacerule.rs
+++ b/components/script/dom/cssfontfacerule.rs
@@ -10,20 +10,19 @@ use dom::cssrule::{CSSRule, SpecificCSSRule};
 use dom::cssstylesheet::CSSStyleSheet;
 use dom::window::Window;
 use dom_struct::dom_struct;
-use parking_lot::RwLock;
 use std::sync::Arc;
 use style::font_face::FontFaceRule;
-use style::shared_lock::ToCssWithGuard;
+use style::shared_lock::{Locked, ToCssWithGuard};
 
 #[dom_struct]
 pub struct CSSFontFaceRule {
     cssrule: CSSRule,
     #[ignore_heap_size_of = "Arc"]
-    fontfacerule: Arc<RwLock<FontFaceRule>>,
+    fontfacerule: Arc<Locked<FontFaceRule>>,
 }
 
 impl CSSFontFaceRule {
-    fn new_inherited(parent_stylesheet: &CSSStyleSheet, fontfacerule: Arc<RwLock<FontFaceRule>>)
+    fn new_inherited(parent_stylesheet: &CSSStyleSheet, fontfacerule: Arc<Locked<FontFaceRule>>)
                      -> CSSFontFaceRule {
         CSSFontFaceRule {
             cssrule: CSSRule::new_inherited(parent_stylesheet),
@@ -33,7 +32,7 @@ impl CSSFontFaceRule {
 
     #[allow(unrooted_must_root)]
     pub fn new(window: &Window, parent_stylesheet: &CSSStyleSheet,
-               fontfacerule: Arc<RwLock<FontFaceRule>>) -> Root<CSSFontFaceRule> {
+               fontfacerule: Arc<Locked<FontFaceRule>>) -> Root<CSSFontFaceRule> {
         reflect_dom_object(box CSSFontFaceRule::new_inherited(parent_stylesheet, fontfacerule),
                            window,
                            CSSFontFaceRuleBinding::Wrap)
@@ -48,6 +47,6 @@ impl SpecificCSSRule for CSSFontFaceRule {
 
     fn get_css(&self) -> DOMString {
         let guard = self.cssrule.shared_lock().read();
-        self.fontfacerule.read().to_css_string(&guard).into()
+        self.fontfacerule.read_with(&guard).to_css_string(&guard).into()
     }
 }
diff --git a/components/script/dom/cssimportrule.rs b/components/script/dom/cssimportrule.rs
index bb01fdfcc84..3c0eb7eb4aa 100644
--- a/components/script/dom/cssimportrule.rs
+++ b/components/script/dom/cssimportrule.rs
@@ -10,21 +10,20 @@ use dom::cssrule::{CSSRule, SpecificCSSRule};
 use dom::cssstylesheet::CSSStyleSheet;
 use dom::window::Window;
 use dom_struct::dom_struct;
-use parking_lot::RwLock;
 use std::sync::Arc;
-use style::shared_lock::ToCssWithGuard;
+use style::shared_lock::{Locked, ToCssWithGuard};
 use style::stylesheets::ImportRule;
 
 #[dom_struct]
 pub struct CSSImportRule {
     cssrule: CSSRule,
     #[ignore_heap_size_of = "Arc"]
-    import_rule: Arc<RwLock<ImportRule>>,
+    import_rule: Arc<Locked<ImportRule>>,
 }
 
 impl CSSImportRule {
     fn new_inherited(parent_stylesheet: &CSSStyleSheet,
-                     import_rule: Arc<RwLock<ImportRule>>)
+                     import_rule: Arc<Locked<ImportRule>>)
                      -> Self {
         CSSImportRule {
             cssrule: CSSRule::new_inherited(parent_stylesheet),
@@ -35,7 +34,7 @@ impl CSSImportRule {
     #[allow(unrooted_must_root)]
     pub fn new(window: &Window,
                parent_stylesheet: &CSSStyleSheet,
-               import_rule: Arc<RwLock<ImportRule>>) -> Root<Self> {
+               import_rule: Arc<Locked<ImportRule>>) -> Root<Self> {
         reflect_dom_object(box Self::new_inherited(parent_stylesheet, import_rule),
                            window,
                            CSSImportRuleBinding::Wrap)
@@ -50,6 +49,6 @@ impl SpecificCSSRule for CSSImportRule {
 
     fn get_css(&self) -> DOMString {
         let guard = self.cssrule.shared_lock().read();
-        self.import_rule.read().to_css_string(&guard).into()
+        self.import_rule.read_with(&guard).to_css_string(&guard).into()
     }
 }
diff --git a/components/script/dom/csskeyframesrule.rs b/components/script/dom/csskeyframesrule.rs
index 330b1be3627..d17eeeb51b5 100644
--- a/components/script/dom/csskeyframesrule.rs
+++ b/components/script/dom/csskeyframesrule.rs
@@ -16,24 +16,23 @@ use dom::cssrulelist::{CSSRuleList, RulesSource};
 use dom::cssstylesheet::CSSStyleSheet;
 use dom::window::Window;
 use dom_struct::dom_struct;
-use parking_lot::RwLock;
 use servo_atoms::Atom;
 use std::sync::Arc;
 use style::keyframes::{Keyframe, KeyframeSelector};
 use style::parser::ParserContextExtraData;
-use style::shared_lock::ToCssWithGuard;
+use style::shared_lock::{Locked, ToCssWithGuard};
 use style::stylesheets::KeyframesRule;
 
 #[dom_struct]
 pub struct CSSKeyframesRule {
     cssrule: CSSRule,
     #[ignore_heap_size_of = "Arc"]
-    keyframesrule: Arc<RwLock<KeyframesRule>>,
+    keyframesrule: Arc<Locked<KeyframesRule>>,
     rulelist: MutNullableJS<CSSRuleList>,
 }
 
 impl CSSKeyframesRule {
-    fn new_inherited(parent_stylesheet: &CSSStyleSheet, keyframesrule: Arc<RwLock<KeyframesRule>>)
+    fn new_inherited(parent_stylesheet: &CSSStyleSheet, keyframesrule: Arc<Locked<KeyframesRule>>)
                      -> CSSKeyframesRule {
         CSSKeyframesRule {
             cssrule: CSSRule::new_inherited(parent_stylesheet),
@@ -44,7 +43,7 @@ impl CSSKeyframesRule {
 
     #[allow(unrooted_must_root)]
     pub fn new(window: &Window, parent_stylesheet: &CSSStyleSheet,
-               keyframesrule: Arc<RwLock<KeyframesRule>>) -> Root<CSSKeyframesRule> {
+               keyframesrule: Arc<Locked<KeyframesRule>>) -> Root<CSSKeyframesRule> {
         reflect_dom_object(box CSSKeyframesRule::new_inherited(parent_stylesheet, keyframesrule),
                            window,
                            CSSKeyframesRuleBinding::Wrap)
@@ -63,9 +62,10 @@ impl CSSKeyframesRule {
     fn find_rule(&self, selector: &str) -> Option<usize> {
         let mut input = Parser::new(selector);
         if let Ok(sel) = KeyframeSelector::parse(&mut input) {
+            let guard = self.cssrule.shared_lock().read();
             // This finds the *last* element matching a selector
             // because that's the rule that applies. Thus, rposition
-            self.keyframesrule.read()
+            self.keyframesrule.read_with(&guard)
                 .keyframes.iter().rposition(|frame| {
                     frame.read().selector == sel
                 })
@@ -86,7 +86,8 @@ impl CSSKeyframesRuleMethods for CSSKeyframesRule {
         let rule = Keyframe::parse(&rule, self.cssrule.parent_stylesheet().style_stylesheet(),
                                    ParserContextExtraData::default());
         if let Ok(rule) = rule {
-            self.keyframesrule.write().keyframes.push(rule);
+            let mut guard = self.cssrule.shared_lock().write();
+            self.keyframesrule.write_with(&mut guard).keyframes.push(rule);
             self.rulelist().append_lazy_dom_rule();
         }
     }
@@ -107,7 +108,8 @@ impl CSSKeyframesRuleMethods for CSSKeyframesRule {
 
     // https://drafts.csswg.org/css-animations/#dom-csskeyframesrule-name
     fn Name(&self) -> DOMString {
-        DOMString::from(&*self.keyframesrule.read().name)
+        let guard = self.cssrule.shared_lock().read();
+        DOMString::from(&*self.keyframesrule.read_with(&guard).name)
     }
 
     // https://drafts.csswg.org/css-animations/#dom-csskeyframesrule-name
@@ -122,7 +124,8 @@ impl CSSKeyframesRuleMethods for CSSKeyframesRule {
             "none" => return Err(Error::Syntax),
             _ => ()
         }
-        self.keyframesrule.write().name = Atom::from(value);
+        let mut guard = self.cssrule.shared_lock().write();
+        self.keyframesrule.write_with(&mut guard).name = Atom::from(value);
         Ok(())
     }
 }
@@ -135,7 +138,7 @@ impl SpecificCSSRule for CSSKeyframesRule {
 
     fn get_css(&self) -> DOMString {
         let guard = self.cssrule.shared_lock().read();
-        self.keyframesrule.read().to_css_string(&guard).into()
+        self.keyframesrule.read_with(&guard).to_css_string(&guard).into()
     }
 
     fn deparent_children(&self) {
diff --git a/components/script/dom/cssmediarule.rs b/components/script/dom/cssmediarule.rs
index 1d1f0846a51..2a07471679e 100644
--- a/components/script/dom/cssmediarule.rs
+++ b/components/script/dom/cssmediarule.rs
@@ -14,10 +14,9 @@ use dom::cssstylesheet::CSSStyleSheet;
 use dom::medialist::MediaList;
 use dom::window::Window;
 use dom_struct::dom_struct;
-use parking_lot::RwLock;
 use std::sync::Arc;
 use style::media_queries::parse_media_query_list;
-use style::shared_lock::ToCssWithGuard;
+use style::shared_lock::{Locked, ToCssWithGuard};
 use style::stylesheets::MediaRule;
 use style_traits::ToCss;
 
@@ -25,14 +24,15 @@ use style_traits::ToCss;
 pub struct CSSMediaRule {
     cssconditionrule: CSSConditionRule,
     #[ignore_heap_size_of = "Arc"]
-    mediarule: Arc<RwLock<MediaRule>>,
+    mediarule: Arc<Locked<MediaRule>>,
     medialist: MutNullableJS<MediaList>,
 }
 
 impl CSSMediaRule {
-    fn new_inherited(parent_stylesheet: &CSSStyleSheet, mediarule: Arc<RwLock<MediaRule>>)
+    fn new_inherited(parent_stylesheet: &CSSStyleSheet, mediarule: Arc<Locked<MediaRule>>)
                      -> CSSMediaRule {
-        let list = mediarule.read().rules.clone();
+        let guard = parent_stylesheet.shared_lock().read();
+        let list = mediarule.read_with(&guard).rules.clone();
         CSSMediaRule {
             cssconditionrule: CSSConditionRule::new_inherited(parent_stylesheet, list),
             mediarule: mediarule,
@@ -42,34 +42,43 @@ impl CSSMediaRule {
 
     #[allow(unrooted_must_root)]
     pub fn new(window: &Window, parent_stylesheet: &CSSStyleSheet,
-               mediarule: Arc<RwLock<MediaRule>>) -> Root<CSSMediaRule> {
+               mediarule: Arc<Locked<MediaRule>>) -> Root<CSSMediaRule> {
         reflect_dom_object(box CSSMediaRule::new_inherited(parent_stylesheet, mediarule),
                            window,
                            CSSMediaRuleBinding::Wrap)
     }
 
     fn medialist(&self) -> Root<MediaList> {
-        self.medialist.or_init(|| MediaList::new(self.global().as_window(),
-                                                 self.cssconditionrule.parent_stylesheet(),
-                                                 self.mediarule.read().media_queries.clone()))
+        self.medialist.or_init(|| {
+            let guard = self.cssconditionrule.shared_lock().read();
+            MediaList::new(self.global().as_window(),
+                           self.cssconditionrule.parent_stylesheet(),
+                           self.mediarule.read_with(&guard).media_queries.clone())
+        })
     }
 
     /// https://drafts.csswg.org/css-conditional-3/#the-cssmediarule-interface
     pub fn get_condition_text(&self) -> DOMString {
         let guard = self.cssconditionrule.shared_lock().read();
-        let rule = self.mediarule.read();
+        let rule = self.mediarule.read_with(&guard);
         let list = rule.media_queries.read_with(&guard);
         list.to_css_string().into()
     }
 
     /// https://drafts.csswg.org/css-conditional-3/#the-cssmediarule-interface
     pub fn set_condition_text(&self, text: DOMString) {
-        let mut guard = self.cssconditionrule.shared_lock().write();
         let mut input = Parser::new(&text);
         let new_medialist = parse_media_query_list(&mut input);
-        let rule = self.mediarule.read();
-        let mut list = rule.media_queries.write_with(&mut guard);
-        *list = new_medialist;
+        let mut guard = self.cssconditionrule.shared_lock().write();
+
+        // Clone an Arc because we can’t borrow `guard` twice at the same time.
+
+        // FIXME(SimonSapin): allow access to multiple objects with one write guard?
+        // Would need a set of usize pointer addresses or something,
+        // the same object is not accessed more than once.
+        let mqs = Arc::clone(&self.mediarule.write_with(&mut guard).media_queries);
+
+        *mqs.write_with(&mut guard) = new_medialist;
     }
 }
 
@@ -81,7 +90,7 @@ impl SpecificCSSRule for CSSMediaRule {
 
     fn get_css(&self) -> DOMString {
         let guard = self.cssconditionrule.shared_lock().read();
-        self.mediarule.read().to_css_string(&guard).into()
+        self.mediarule.read_with(&guard).to_css_string(&guard).into()
     }
 }
 
diff --git a/components/script/dom/cssnamespacerule.rs b/components/script/dom/cssnamespacerule.rs
index 46702c275ba..744a8020667 100644
--- a/components/script/dom/cssnamespacerule.rs
+++ b/components/script/dom/cssnamespacerule.rs
@@ -11,20 +11,19 @@ use dom::cssrule::{CSSRule, SpecificCSSRule};
 use dom::cssstylesheet::CSSStyleSheet;
 use dom::window::Window;
 use dom_struct::dom_struct;
-use parking_lot::RwLock;
 use std::sync::Arc;
-use style::shared_lock::ToCssWithGuard;
+use style::shared_lock::{Locked, ToCssWithGuard};
 use style::stylesheets::NamespaceRule;
 
 #[dom_struct]
 pub struct CSSNamespaceRule {
     cssrule: CSSRule,
     #[ignore_heap_size_of = "Arc"]
-    namespacerule: Arc<RwLock<NamespaceRule>>,
+    namespacerule: Arc<Locked<NamespaceRule>>,
 }
 
 impl CSSNamespaceRule {
-    fn new_inherited(parent_stylesheet: &CSSStyleSheet, namespacerule: Arc<RwLock<NamespaceRule>>)
+    fn new_inherited(parent_stylesheet: &CSSStyleSheet, namespacerule: Arc<Locked<NamespaceRule>>)
                      -> CSSNamespaceRule {
         CSSNamespaceRule {
             cssrule: CSSRule::new_inherited(parent_stylesheet),
@@ -34,7 +33,7 @@ impl CSSNamespaceRule {
 
     #[allow(unrooted_must_root)]
     pub fn new(window: &Window, parent_stylesheet: &CSSStyleSheet,
-               namespacerule: Arc<RwLock<NamespaceRule>>) -> Root<CSSNamespaceRule> {
+               namespacerule: Arc<Locked<NamespaceRule>>) -> Root<CSSNamespaceRule> {
         reflect_dom_object(box CSSNamespaceRule::new_inherited(parent_stylesheet, namespacerule),
                            window,
                            CSSNamespaceRuleBinding::Wrap)
@@ -44,14 +43,16 @@ impl CSSNamespaceRule {
 impl CSSNamespaceRuleMethods for CSSNamespaceRule {
     // https://drafts.csswg.org/cssom/#dom-cssnamespacerule-prefix
     fn Prefix(&self) -> DOMString {
-        self.namespacerule.read().prefix
+        let guard = self.cssrule.shared_lock().read();
+        self.namespacerule.read_with(&guard).prefix
             .as_ref().map(|s| s.to_string().into())
             .unwrap_or(DOMString::new())
     }
 
     // https://drafts.csswg.org/cssom/#dom-cssnamespacerule-namespaceuri
     fn NamespaceURI(&self) -> DOMString {
-        (*self.namespacerule.read().url).into()
+        let guard = self.cssrule.shared_lock().read();
+        (*self.namespacerule.read_with(&guard).url).into()
     }
 }
 
@@ -63,6 +64,6 @@ impl SpecificCSSRule for CSSNamespaceRule {
 
     fn get_css(&self) -> DOMString {
         let guard = self.cssrule.shared_lock().read();
-        self.namespacerule.read().to_css_string(&guard).into()
+        self.namespacerule.read_with(&guard).to_css_string(&guard).into()
     }
 }
diff --git a/components/script/dom/cssrulelist.rs b/components/script/dom/cssrulelist.rs
index 6321296c785..bc77361b5ae 100644
--- a/components/script/dom/cssrulelist.rs
+++ b/components/script/dom/cssrulelist.rs
@@ -13,7 +13,6 @@ use dom::cssrule::CSSRule;
 use dom::cssstylesheet::CSSStyleSheet;
 use dom::window::Window;
 use dom_struct::dom_struct;
-use parking_lot::RwLock;
 use std::sync::Arc;
 use style::shared_lock::Locked;
 use style::stylesheets::{CssRules, KeyframesRule, RulesMutateError};
@@ -45,19 +44,19 @@ pub struct CSSRuleList {
 
 pub enum RulesSource {
     Rules(Arc<Locked<CssRules>>),
-    Keyframes(Arc<RwLock<KeyframesRule>>),
+    Keyframes(Arc<Locked<KeyframesRule>>),
 }
 
 impl CSSRuleList {
     #[allow(unrooted_must_root)]
     pub fn new_inherited(parent_stylesheet: &CSSStyleSheet, rules: RulesSource) -> CSSRuleList {
+        let guard = parent_stylesheet.shared_lock().read();
         let dom_rules = match rules {
             RulesSource::Rules(ref rules) => {
-                let guard = parent_stylesheet.shared_lock().read();
                 rules.read_with(&guard).0.iter().map(|_| MutNullableJS::new(None)).collect()
             }
             RulesSource::Keyframes(ref rules) => {
-                rules.read().keyframes.iter().map(|_| MutNullableJS::new(None)).collect()
+                rules.read_with(&guard).keyframes.iter().map(|_| MutNullableJS::new(None)).collect()
             }
         };
 
@@ -104,10 +103,10 @@ impl CSSRuleList {
     // In case of a keyframe rule, index must be valid.
     pub fn remove_rule(&self, index: u32) -> ErrorResult {
         let index = index as usize;
+        let mut guard = self.parent_stylesheet.shared_lock().write();
 
         match self.rules {
             RulesSource::Rules(ref css_rules) => {
-                let mut guard = self.parent_stylesheet.shared_lock().write();
                 css_rules.write_with(&mut guard).remove_rule(index)?;
                 let mut dom_rules = self.dom_rules.borrow_mut();
                 dom_rules[index].get().map(|r| r.detach());
@@ -119,7 +118,7 @@ impl CSSRuleList {
                 let mut dom_rules = self.dom_rules.borrow_mut();
                 dom_rules[index].get().map(|r| r.detach());
                 dom_rules.remove(index);
-                kf.write().keyframes.remove(index);
+                kf.write_with(&mut guard).keyframes.remove(index);
                 Ok(())
             }
         }
@@ -136,9 +135,9 @@ impl CSSRuleList {
         self.dom_rules.borrow().get(idx as usize).map(|rule| {
             rule.or_init(|| {
                 let parent_stylesheet = &self.parent_stylesheet;
+                let guard = parent_stylesheet.shared_lock().read();
                 match self.rules {
                     RulesSource::Rules(ref rules) => {
-                        let guard = parent_stylesheet.shared_lock().read();
                         CSSRule::new_specific(self.global().as_window(),
                                              parent_stylesheet,
                                              rules.read_with(&guard).0[idx as usize].clone())
@@ -146,7 +145,7 @@ impl CSSRuleList {
                     RulesSource::Keyframes(ref rules) => {
                         Root::upcast(CSSKeyframeRule::new(self.global().as_window(),
                                                           parent_stylesheet,
-                                                          rules.read()
+                                                          rules.read_with(&guard)
                                                                 .keyframes[idx as usize]
                                                                 .clone()))
                     }
diff --git a/components/script/dom/csssupportsrule.rs b/components/script/dom/csssupportsrule.rs
index d5e844e52aa..7ba3a24d038 100644
--- a/components/script/dom/csssupportsrule.rs
+++ b/components/script/dom/csssupportsrule.rs
@@ -13,10 +13,9 @@ use dom::cssrule::SpecificCSSRule;
 use dom::cssstylesheet::CSSStyleSheet;
 use dom::window::Window;
 use dom_struct::dom_struct;
-use parking_lot::RwLock;
 use std::sync::Arc;
 use style::parser::ParserContext;
-use style::shared_lock::ToCssWithGuard;
+use style::shared_lock::{Locked, ToCssWithGuard};
 use style::stylesheets::SupportsRule;
 use style::supports::SupportsCondition;
 use style_traits::ToCss;
@@ -25,13 +24,14 @@ use style_traits::ToCss;
 pub struct CSSSupportsRule {
     cssconditionrule: CSSConditionRule,
     #[ignore_heap_size_of = "Arc"]
-    supportsrule: Arc<RwLock<SupportsRule>>,
+    supportsrule: Arc<Locked<SupportsRule>>,
 }
 
 impl CSSSupportsRule {
-    fn new_inherited(parent_stylesheet: &CSSStyleSheet, supportsrule: Arc<RwLock<SupportsRule>>)
+    fn new_inherited(parent_stylesheet: &CSSStyleSheet, supportsrule: Arc<Locked<SupportsRule>>)
                      -> CSSSupportsRule {
-        let list = supportsrule.read().rules.clone();
+        let guard = parent_stylesheet.shared_lock().read();
+        let list = supportsrule.read_with(&guard).rules.clone();
         CSSSupportsRule {
             cssconditionrule: CSSConditionRule::new_inherited(parent_stylesheet, list),
             supportsrule: supportsrule,
@@ -40,7 +40,7 @@ impl CSSSupportsRule {
 
     #[allow(unrooted_must_root)]
     pub fn new(window: &Window, parent_stylesheet: &CSSStyleSheet,
-               supportsrule: Arc<RwLock<SupportsRule>>) -> Root<CSSSupportsRule> {
+               supportsrule: Arc<Locked<SupportsRule>>) -> Root<CSSSupportsRule> {
         reflect_dom_object(box CSSSupportsRule::new_inherited(parent_stylesheet, supportsrule),
                            window,
                            CSSSupportsRuleBinding::Wrap)
@@ -48,7 +48,8 @@ impl CSSSupportsRule {
 
     /// https://drafts.csswg.org/css-conditional-3/#the-csssupportsrule-interface
     pub fn get_condition_text(&self) -> DOMString {
-        let rule = self.supportsrule.read();
+        let guard = self.cssconditionrule.shared_lock().read();
+        let rule = self.supportsrule.read_with(&guard);
         rule.condition.to_css_string().into()
     }
 
@@ -62,7 +63,8 @@ impl CSSSupportsRule {
             let url = win.Document().url();
             let context = ParserContext::new_for_cssom(&url, win.css_error_reporter());
             let enabled = cond.eval(&context);
-            let mut rule = self.supportsrule.write();
+            let mut guard = self.cssconditionrule.shared_lock().write();
+            let rule = self.supportsrule.write_with(&mut guard);
             rule.condition = cond;
             rule.enabled = enabled;
         }
@@ -77,6 +79,6 @@ impl SpecificCSSRule for CSSSupportsRule {
 
     fn get_css(&self) -> DOMString {
         let guard = self.cssconditionrule.shared_lock().read();
-        self.supportsrule.read().to_css_string(&guard).into()
+        self.supportsrule.read_with(&guard).to_css_string(&guard).into()
     }
 }
diff --git a/components/script/dom/cssviewportrule.rs b/components/script/dom/cssviewportrule.rs
index 855c8bdda57..38abf909ff0 100644
--- a/components/script/dom/cssviewportrule.rs
+++ b/components/script/dom/cssviewportrule.rs
@@ -10,20 +10,19 @@ use dom::cssrule::{CSSRule, SpecificCSSRule};
 use dom::cssstylesheet::CSSStyleSheet;
 use dom::window::Window;
 use dom_struct::dom_struct;
-use parking_lot::RwLock;
 use std::sync::Arc;
-use style::shared_lock::ToCssWithGuard;
+use style::shared_lock::{Locked, ToCssWithGuard};
 use style::viewport::ViewportRule;
 
 #[dom_struct]
 pub struct CSSViewportRule {
     cssrule: CSSRule,
     #[ignore_heap_size_of = "Arc"]
-    viewportrule: Arc<RwLock<ViewportRule>>,
+    viewportrule: Arc<Locked<ViewportRule>>,
 }
 
 impl CSSViewportRule {
-    fn new_inherited(parent_stylesheet: &CSSStyleSheet, viewportrule: Arc<RwLock<ViewportRule>>) -> CSSViewportRule {
+    fn new_inherited(parent_stylesheet: &CSSStyleSheet, viewportrule: Arc<Locked<ViewportRule>>) -> CSSViewportRule {
         CSSViewportRule {
             cssrule: CSSRule::new_inherited(parent_stylesheet),
             viewportrule: viewportrule,
@@ -32,7 +31,7 @@ impl CSSViewportRule {
 
     #[allow(unrooted_must_root)]
     pub fn new(window: &Window, parent_stylesheet: &CSSStyleSheet,
-               viewportrule: Arc<RwLock<ViewportRule>>) -> Root<CSSViewportRule> {
+               viewportrule: Arc<Locked<ViewportRule>>) -> Root<CSSViewportRule> {
         reflect_dom_object(box CSSViewportRule::new_inherited(parent_stylesheet, viewportrule),
                            window,
                            CSSViewportRuleBinding::Wrap)
@@ -47,6 +46,6 @@ impl SpecificCSSRule for CSSViewportRule {
 
     fn get_css(&self) -> DOMString {
         let guard = self.cssrule.shared_lock().read();
-        self.viewportrule.read().to_css_string(&guard).into()
+        self.viewportrule.read_with(&guard).to_css_string(&guard).into()
     }
 }
diff --git a/components/script/dom/htmlmetaelement.rs b/components/script/dom/htmlmetaelement.rs
index a564c6b2661..bc6f37561d8 100644
--- a/components/script/dom/htmlmetaelement.rs
+++ b/components/script/dom/htmlmetaelement.rs
@@ -19,7 +19,6 @@ use dom::node::{Node, UnbindContext, document_from_node, window_from_node};
 use dom::virtualmethods::VirtualMethods;
 use dom_struct::dom_struct;
 use html5ever_atoms::LocalName;
-use parking_lot::RwLock;
 use servo_config::prefs::PREFS;
 use std::ascii::AsciiExt;
 use std::sync::Arc;
@@ -101,7 +100,7 @@ impl HTMLMetaElement {
                 if let Some(translated_rule) = ViewportRule::from_meta(&**content) {
                     let document = self.upcast::<Node>().owner_doc();
                     let shared_lock = document.style_shared_lock();
-                    let rule = CssRule::Viewport(Arc::new(RwLock::new(translated_rule)));
+                    let rule = CssRule::Viewport(Arc::new(shared_lock.wrap(translated_rule)));
                     *self.stylesheet.borrow_mut() = Some(Arc::new(Stylesheet {
                         rules: CssRules::new(vec![rule], shared_lock),
                         origin: Origin::Author,
diff --git a/components/script/stylesheet_loader.rs b/components/script/stylesheet_loader.rs
index 79b90be7426..db21ee795fd 100644
--- a/components/script/stylesheet_loader.rs
+++ b/components/script/stylesheet_loader.rs
@@ -22,13 +22,13 @@ use ipc_channel::router::ROUTER;
 use net_traits::{FetchResponseListener, FetchMetadata, FilteredMetadata, Metadata, NetworkError, ReferrerPolicy};
 use net_traits::request::{CorsSettings, CredentialsMode, Destination, RequestInit, RequestMode, Type as RequestType};
 use network_listener::{NetworkListener, PreInvoke};
-use parking_lot::RwLock;
 use script_layout_interface::message::Msg;
 use servo_url::ServoUrl;
 use std::mem;
 use std::sync::{Arc, Mutex};
 use style::media_queries::MediaList;
 use style::parser::ParserContextExtraData;
+use style::shared_lock::Locked as StyleLocked;
 use style::stylesheets::{ImportRule, Stylesheet, Origin};
 use style::stylesheets::StylesheetLoader as StyleStylesheetLoader;
 
@@ -55,15 +55,16 @@ pub trait StylesheetOwner {
 pub enum StylesheetContextSource {
     // NB: `media` is just an option so we avoid cloning it.
     LinkElement { media: Option<MediaList>, url: ServoUrl },
-    Import(Arc<RwLock<ImportRule>>),
+    Import(Arc<StyleLocked<ImportRule>>),
 }
 
 impl StylesheetContextSource {
-    fn url(&self) -> ServoUrl {
+    fn url(&self, document: &Document) -> ServoUrl {
         match *self {
             StylesheetContextSource::LinkElement { ref url, .. } => url.clone(),
             StylesheetContextSource::Import(ref import) => {
-                let import = import.read();
+                let guard = document.style_shared_lock().read();
+                let import = import.read_with(&guard);
                 // Look at the parser in style::stylesheets, where we don't
                 // trigger a load if the url is invalid.
                 import.url.url()
@@ -174,9 +175,16 @@ impl FetchResponseListener for StylesheetContext {
                     }
                 }
                 StylesheetContextSource::Import(ref import) => {
-                    let import = import.read();
                     let mut guard = document.style_shared_lock().write();
-                    Stylesheet::update_from_bytes(&import.stylesheet,
+
+                    // Clone an Arc because we can’t borrow `guard` twice at the same time.
+
+                    // FIXME(SimonSapin): allow access to multiple objects with one write guard?
+                    // Would need a set of usize pointer addresses or something,
+                    // the same object is not accessed more than once.
+                    let stylesheet = Arc::clone(&import.write_with(&mut guard).stylesheet);
+
+                    Stylesheet::update_from_bytes(&stylesheet,
                                                   &data,
                                                   protocol_encoding_label,
                                                   Some(environment_encoding),
@@ -201,7 +209,7 @@ impl FetchResponseListener for StylesheetContext {
             document.decrement_script_blocking_stylesheet_count();
         }
 
-        let url = self.source.url();
+        let url = self.source.url(&document);
         document.finish_load(LoadType::Stylesheet(url));
 
         if let Some(any_failed) = owner.load_finished(successful) {
@@ -226,8 +234,8 @@ impl<'a> StylesheetLoader<'a> {
 impl<'a> StylesheetLoader<'a> {
     pub fn load(&self, source: StylesheetContextSource, cors_setting: Option<CorsSettings>,
                 integrity_metadata: String) {
-        let url = source.url();
         let document = document_from_node(self.elem);
+        let url = source.url(&document);
         let gen = self.elem.downcast::<HTMLLinkElement>()
                            .map(HTMLLinkElement::get_request_generation_id);
         let context = Arc::new(Mutex::new(StylesheetContext {
@@ -289,7 +297,7 @@ impl<'a> StylesheetLoader<'a> {
 }
 
 impl<'a> StyleStylesheetLoader for StylesheetLoader<'a> {
-    fn request_stylesheet(&self, import: &Arc<RwLock<ImportRule>>) {
+    fn request_stylesheet(&self, import: &Arc<StyleLocked<ImportRule>>) {
         //TODO (mrnayak) : Whether we should use the original loader's CORS setting?
         //Fix this when spec has more details.
         self.load(StylesheetContextSource::Import(import.clone()), None, "".to_owned())
diff --git a/components/style/gecko/arc_types.rs b/components/style/gecko/arc_types.rs
index 798af00906e..58ec43cf387 100644
--- a/components/style/gecko/arc_types.rs
+++ b/components/style/gecko/arc_types.rs
@@ -51,10 +51,21 @@ impl_arc_ffi!(ComputedValues => ServoComputedValues
 impl_arc_ffi!(RwLock<PropertyDeclarationBlock> => RawServoDeclarationBlock
               [Servo_DeclarationBlock_AddRef, Servo_DeclarationBlock_Release]);
 
+/// FIXME: Remove once StyleRule is actually in Locked<_>
+pub trait HackHackHack {
+    fn as_arc<'a>(ptr: &'a &RawServoStyleRule) -> &'a ::std::sync::Arc<RwLock<StyleRule>>;
+}
+
+impl HackHackHack for Locked<StyleRule> {
+    fn as_arc<'a>(ptr: &'a &RawServoStyleRule) -> &'a ::std::sync::Arc<RwLock<StyleRule>> {
+        RwLock::<StyleRule>::as_arc(ptr)
+    }
+}
+
 impl_arc_ffi!(RwLock<StyleRule> => RawServoStyleRule
               [Servo_StyleRule_AddRef, Servo_StyleRule_Release]);
 
-impl_arc_ffi!(RwLock<ImportRule> => RawServoImportRule
+impl_arc_ffi!(Locked<ImportRule> => RawServoImportRule
               [Servo_ImportRule_AddRef, Servo_ImportRule_Release]);
 
 impl_arc_ffi!(AnimationValue => RawServoAnimationValue
@@ -66,8 +77,8 @@ impl_arc_ffi!(RwLock<AnimationValueMap> => RawServoAnimationValueMap
 impl_arc_ffi!(Locked<MediaList> => RawServoMediaList
               [Servo_MediaList_AddRef, Servo_MediaList_Release]);
 
-impl_arc_ffi!(RwLock<MediaRule> => RawServoMediaRule
+impl_arc_ffi!(Locked<MediaRule> => RawServoMediaRule
               [Servo_MediaRule_AddRef, Servo_MediaRule_Release]);
 
-impl_arc_ffi!(RwLock<NamespaceRule> => RawServoNamespaceRule
+impl_arc_ffi!(Locked<NamespaceRule> => RawServoNamespaceRule
               [Servo_NamespaceRule_AddRef, Servo_NamespaceRule_Release]);
diff --git a/components/style/stylesheets.rs b/components/style/stylesheets.rs
index 07dc2632b2d..a0f0baa3840 100644
--- a/components/style/stylesheets.rs
+++ b/components/style/stylesheets.rs
@@ -213,14 +213,14 @@ pub enum CssRule {
     // No Charset here, CSSCharsetRule has been removed from CSSOM
     // https://drafts.csswg.org/cssom/#changes-from-5-december-2013
 
-    Namespace(Arc<RwLock<NamespaceRule>>),
-    Import(Arc<RwLock<ImportRule>>),
+    Namespace(Arc<Locked<NamespaceRule>>),
+    Import(Arc<Locked<ImportRule>>),
     Style(Arc<RwLock<StyleRule>>),
-    Media(Arc<RwLock<MediaRule>>),
-    FontFace(Arc<RwLock<FontFaceRule>>),
-    Viewport(Arc<RwLock<ViewportRule>>),
-    Keyframes(Arc<RwLock<KeyframesRule>>),
-    Supports(Arc<RwLock<SupportsRule>>),
+    Media(Arc<Locked<MediaRule>>),
+    FontFace(Arc<Locked<FontFaceRule>>),
+    Viewport(Arc<Locked<ViewportRule>>),
+    Keyframes(Arc<Locked<KeyframesRule>>),
+    Supports(Arc<Locked<SupportsRule>>),
 }
 
 #[allow(missing_docs)]
@@ -301,7 +301,7 @@ impl CssRule {
     where F: FnMut(&[CssRule], Option<&MediaList>) -> R {
         match *self {
             CssRule::Import(ref lock) => {
-                let rule = lock.read();
+                let rule = lock.read_with(guard);
                 let media = rule.stylesheet.media.read_with(guard);
                 let rules = rule.stylesheet.rules.read_with(guard);
                 // FIXME(emilio): Include the nested rules if the stylesheet is
@@ -316,13 +316,13 @@ impl CssRule {
                 f(&[], None)
             }
             CssRule::Media(ref lock) => {
-                let media_rule = lock.read();
+                let media_rule = lock.read_with(guard);
                 let mq = media_rule.media_queries.read_with(guard);
                 let rules = &media_rule.rules.read_with(guard).0;
                 f(rules, Some(&mq))
             }
             CssRule::Supports(ref lock) => {
-                let supports_rule = lock.read();
+                let supports_rule = lock.read_with(guard);
                 let enabled = supports_rule.enabled;
                 if enabled {
                     let rules = &supports_rule.rules.read_with(guard).0;
@@ -378,14 +378,14 @@ impl ToCssWithGuard for CssRule {
     fn to_css<W>(&self, guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
     where W: fmt::Write {
         match *self {
-            CssRule::Namespace(ref lock) => lock.read().to_css(guard, dest),
-            CssRule::Import(ref lock) => lock.read().to_css(guard, dest),
+            CssRule::Namespace(ref lock) => lock.read_with(guard).to_css(guard, dest),
+            CssRule::Import(ref lock) => lock.read_with(guard).to_css(guard, dest),
             CssRule::Style(ref lock) => lock.read().to_css(guard, dest),
-            CssRule::FontFace(ref lock) => lock.read().to_css(guard, dest),
-            CssRule::Viewport(ref lock) => lock.read().to_css(guard, dest),
-            CssRule::Keyframes(ref lock) => lock.read().to_css(guard, dest),
-            CssRule::Media(ref lock) => lock.read().to_css(guard, dest),
-            CssRule::Supports(ref lock) => lock.read().to_css(guard, dest),
+            CssRule::FontFace(ref lock) => lock.read_with(guard).to_css(guard, dest),
+            CssRule::Viewport(ref lock) => lock.read_with(guard).to_css(guard, dest),
+            CssRule::Keyframes(ref lock) => lock.read_with(guard).to_css(guard, dest),
+            CssRule::Media(ref lock) => lock.read_with(guard).to_css(guard, dest),
+            CssRule::Supports(ref lock) => lock.read_with(guard).to_css(guard, dest),
         }
     }
 }
@@ -717,7 +717,7 @@ macro_rules! rule_filter {
                 where F: FnMut(&$rule_type) {
                     self.effective_rules(device, guard, |rule| {
                         if let CssRule::$variant(ref lock) = *rule {
-                            let rule = lock.read();
+                            let rule = lock.read_with(guard);
                             f(&rule)
                         }
                     })
@@ -736,6 +736,18 @@ rule_filter! {
     effective_supports_rules(Supports => SupportsRule),
 }
 
+/// FIXME: Remove once StyleRule is actually in Locked<_>
+pub trait RwLockStyleRulePretendLockedStyleRule<T> {
+    /// Pretend we’re Locked<_>
+    fn read_with(&self, guard: &SharedRwLockReadGuard) -> ::parking_lot::RwLockReadGuard<T>;
+}
+
+impl RwLockStyleRulePretendLockedStyleRule<StyleRule> for RwLock<StyleRule> {
+    fn read_with(&self, _: &SharedRwLockReadGuard) -> ::parking_lot::RwLockReadGuard<StyleRule> {
+        self.read()
+    }
+}
+
 /// The stylesheet loader is the abstraction used to trigger network requests
 /// for `@import` rules.
 pub trait StylesheetLoader {
@@ -743,7 +755,7 @@ pub trait StylesheetLoader {
     ///
     /// The called code is responsible to update the `stylesheet` rules field
     /// when the sheet is done loading.
-    fn request_stylesheet(&self, import: &Arc<RwLock<ImportRule>>);
+    fn request_stylesheet(&self, import: &Arc<Locked<ImportRule>>);
 }
 
 struct TopLevelRuleParser<'a> {
@@ -811,7 +823,7 @@ impl<'a> AtRuleParser for TopLevelRuleParser<'a> {
 
                     let is_valid_url = url.url().is_some();
 
-                    let import_rule = Arc::new(RwLock::new(
+                    let import_rule = Arc::new(self.shared_lock.wrap(
                         ImportRule {
                             url: url,
                             stylesheet: Arc::new(Stylesheet {
@@ -855,12 +867,12 @@ impl<'a> AtRuleParser for TopLevelRuleParser<'a> {
                         None
                     };
 
-                    return Ok(AtRuleType::WithoutBlock(CssRule::Namespace(Arc::new(RwLock::new(
-                        NamespaceRule {
+                    return Ok(AtRuleType::WithoutBlock(CssRule::Namespace(Arc::new(
+                        self.shared_lock.wrap(NamespaceRule {
                             prefix: opt_prefix,
                             url: url,
-                        }
-                    )))))
+                        })
+                    ))))
                 } else {
                     self.state.set(State::Invalid);
                     return Err(())  // "@namespace must be before any rule but @charset and @import"
@@ -973,29 +985,29 @@ impl<'a, 'b> AtRuleParser for NestedRuleParser<'a, 'b> {
     fn parse_block(&mut self, prelude: AtRulePrelude, input: &mut Parser) -> Result<CssRule, ()> {
         match prelude {
             AtRulePrelude::FontFace => {
-                Ok(CssRule::FontFace(Arc::new(RwLock::new(
+                Ok(CssRule::FontFace(Arc::new(self.shared_lock.wrap(
                     try!(parse_font_face_block(self.context, input))))))
             }
             AtRulePrelude::Media(media_queries) => {
-                Ok(CssRule::Media(Arc::new(RwLock::new(MediaRule {
+                Ok(CssRule::Media(Arc::new(self.shared_lock.wrap(MediaRule {
                     media_queries: media_queries,
                     rules: self.parse_nested_rules(input),
                 }))))
             }
             AtRulePrelude::Supports(cond) => {
                 let enabled = cond.eval(self.context);
-                Ok(CssRule::Supports(Arc::new(RwLock::new(SupportsRule {
+                Ok(CssRule::Supports(Arc::new(self.shared_lock.wrap(SupportsRule {
                     condition: cond,
                     rules: self.parse_nested_rules(input),
                     enabled: enabled,
                 }))))
             }
             AtRulePrelude::Viewport => {
-                Ok(CssRule::Viewport(Arc::new(RwLock::new(
+                Ok(CssRule::Viewport(Arc::new(self.shared_lock.wrap(
                     try!(ViewportRule::parse(input, self.context))))))
             }
             AtRulePrelude::Keyframes(name) => {
-                Ok(CssRule::Keyframes(Arc::new(RwLock::new(KeyframesRule {
+                Ok(CssRule::Keyframes(Arc::new(self.shared_lock.wrap(KeyframesRule {
                     name: name,
                     keyframes: parse_keyframe_list(&self.context, input),
                 }))))
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index 73684a4b8fd..4e6b6350beb 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -274,11 +274,11 @@ impl Stylist {
                     }
                 }
                 CssRule::Import(ref import) => {
-                    let import = import.read();
+                    let import = import.read_with(guard);
                     self.add_stylesheet(&import.stylesheet, guard)
                 }
                 CssRule::Keyframes(ref keyframes_rule) => {
-                    let keyframes_rule = keyframes_rule.read();
+                    let keyframes_rule = keyframes_rule.read_with(guard);
                     debug!("Found valid keyframes rule: {:?}", *keyframes_rule);
                     let animation = KeyframesAnimation::from_keyframes(&keyframes_rule.keyframes);
                     debug!("Found valid keyframe animation: {:?}", animation);
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index e260f365fa5..24380439062 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -23,6 +23,7 @@ use style::context::{ThreadLocalStyleContext, ThreadLocalStyleContextCreationInf
 use style::data::{ElementData, ElementStyles, RestyleData};
 use style::dom::{ShowSubtreeData, TElement, TNode};
 use style::error_reporting::StdoutErrorReporter;
+use style::gecko::arc_types::HackHackHack;
 use style::gecko::data::{PerDocumentStyleData, PerDocumentStyleDataImpl};
 use style::gecko::restyle_damage::GeckoRestyleDamage;
 use style::gecko::selector_parser::{SelectorImpl, PseudoElement};
@@ -81,6 +82,7 @@ use style::string_cache::Atom;
 use style::stylesheets::{CssRule, CssRules, ImportRule, MediaRule, NamespaceRule};
 use style::stylesheets::{Origin, Stylesheet, StyleRule};
 use style::stylesheets::StylesheetLoader as StyleStylesheetLoader;
+use style::stylesheets::RwLockStyleRulePretendLockedStyleRule;
 use style::supports::parse_condition_or_declaration;
 use style::thread_state;
 use style::timer::Timer;
@@ -586,17 +588,19 @@ macro_rules! impl_basic_rule_funcs {
 
         #[no_mangle]
         pub extern "C" fn $debug(rule: &$raw_type, result: *mut nsACString) {
-            let rule = RwLock::<$rule_type>::as_arc(&rule);
+            let global_style_data = &*GLOBAL_STYLE_DATA;
+            let guard = global_style_data.shared_lock.read();
+            let rule = Locked::<$rule_type>::as_arc(&rule);
             let result = unsafe { result.as_mut().unwrap() };
-            write!(result, "{:?}", *rule.read()).unwrap();
+            write!(result, "{:?}", *rule.read_with(&guard)).unwrap();
         }
 
         #[no_mangle]
         pub extern "C" fn $to_css(rule: &$raw_type, result: *mut nsAString) {
             let global_style_data = &*GLOBAL_STYLE_DATA;
             let guard = global_style_data.shared_lock.read();
-            let rule = RwLock::<$rule_type>::as_arc(&rule);
-            rule.read().to_css(&guard, unsafe { result.as_mut().unwrap() }).unwrap();
+            let rule = Locked::<$rule_type>::as_arc(&rule);
+            rule.read_with(&guard).to_css(&guard, unsafe { result.as_mut().unwrap() }).unwrap();
         }
     }
 }
@@ -641,26 +645,34 @@ pub extern "C" fn Servo_StyleRule_GetSelectorText(rule: RawServoStyleRuleBorrowe
 
 #[no_mangle]
 pub extern "C" fn Servo_MediaRule_GetMedia(rule: RawServoMediaRuleBorrowed) -> RawServoMediaListStrong {
-    let rule = RwLock::<MediaRule>::as_arc(&rule);
-    rule.read().media_queries.clone().into_strong()
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let rule = Locked::<MediaRule>::as_arc(&rule);
+    rule.read_with(&guard).media_queries.clone().into_strong()
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_MediaRule_GetRules(rule: RawServoMediaRuleBorrowed) -> ServoCssRulesStrong {
-    let rule = RwLock::<MediaRule>::as_arc(&rule);
-    rule.read().rules.clone().into_strong()
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let rule = Locked::<MediaRule>::as_arc(&rule);
+    rule.read_with(&guard).rules.clone().into_strong()
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_NamespaceRule_GetPrefix(rule: RawServoNamespaceRuleBorrowed) -> *mut nsIAtom {
-    let rule = RwLock::<NamespaceRule>::as_arc(&rule);
-    rule.read().prefix.as_ref().unwrap_or(&atom!("")).as_ptr()
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let rule = Locked::<NamespaceRule>::as_arc(&rule);
+    rule.read_with(&guard).prefix.as_ref().unwrap_or(&atom!("")).as_ptr()
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_NamespaceRule_GetURI(rule: RawServoNamespaceRuleBorrowed) -> *mut nsIAtom {
-    let rule = RwLock::<NamespaceRule>::as_arc(&rule);
-    rule.read().url.0.as_ptr()
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let rule = Locked::<NamespaceRule>::as_arc(&rule);
+    rule.read_with(&guard).url.0.as_ptr()
 }
 
 #[no_mangle]
@@ -1404,8 +1416,10 @@ pub extern "C" fn Servo_NoteExplicitHints(element: RawGeckoElementBorrowed,
 pub extern "C" fn Servo_ImportRule_GetSheet(import_rule:
                                             RawServoImportRuleBorrowed)
                                             -> RawServoStyleSheetStrong {
-    let import_rule = RwLock::<ImportRule>::as_arc(&import_rule);
-    import_rule.read().stylesheet.clone().into_strong()
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let import_rule = Locked::<ImportRule>::as_arc(&import_rule);
+    import_rule.read_with(&guard).stylesheet.clone().into_strong()
 }
 
 #[no_mangle]
diff --git a/ports/geckolib/stylesheet_loader.rs b/ports/geckolib/stylesheet_loader.rs
index bcd55cce2fd..2e81de1a57e 100644
--- a/ports/geckolib/stylesheet_loader.rs
+++ b/ports/geckolib/stylesheet_loader.rs
@@ -2,11 +2,11 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use parking_lot::RwLock;
 use std::sync::Arc;
 use style::gecko_bindings::bindings::Gecko_LoadStyleSheet;
 use style::gecko_bindings::structs::{Loader, ServoStyleSheet};
 use style::gecko_bindings::sugar::ownership::HasArcFFI;
+use style::shared_lock::Locked;
 use style::stylesheets::{ImportRule, StylesheetLoader as StyleStylesheetLoader};
 use style_traits::ToCss;
 use super::glue::GLOBAL_STYLE_DATA;
@@ -20,10 +20,10 @@ impl StylesheetLoader {
 }
 
 impl StyleStylesheetLoader for StylesheetLoader {
-    fn request_stylesheet(&self, import_rule: &Arc<RwLock<ImportRule>>) {
+    fn request_stylesheet(&self, import_rule: &Arc<Locked<ImportRule>>) {
         let global_style_data = &*GLOBAL_STYLE_DATA;
         let guard = global_style_data.shared_lock.read();
-        let import = import_rule.read();
+        let import = import_rule.read_with(&guard);
         let (spec_bytes, spec_len) = import.url.as_slice_components()
             .expect("Import only loads valid URLs");
 
diff --git a/tests/unit/style/stylesheets.rs b/tests/unit/style/stylesheets.rs
index 00cefe23ce9..a1c67932b53 100644
--- a/tests/unit/style/stylesheets.rs
+++ b/tests/unit/style/stylesheets.rs
@@ -77,7 +77,7 @@ fn test_parse_stylesheet() {
         dirty_on_viewport_size_change: AtomicBool::new(false),
         disabled: AtomicBool::new(false),
         rules: CssRules::new(vec![
-            CssRule::Namespace(Arc::new(RwLock::new(NamespaceRule {
+            CssRule::Namespace(Arc::new(stylesheet.shared_lock.wrap(NamespaceRule {
                 prefix: None,
                 url: NsAtom::from("http://www.w3.org/1999/xhtml")
             }))),
@@ -235,7 +235,7 @@ fn test_parse_stylesheet() {
                      Importance::Normal),
                 ]))),
             }))),
-            CssRule::Keyframes(Arc::new(RwLock::new(KeyframesRule {
+            CssRule::Keyframes(Arc::new(stylesheet.shared_lock.wrap(KeyframesRule {
                 name: "foo".into(),
                 keyframes: vec![
                     Arc::new(RwLock::new(Keyframe {

From 57724e5a3755a757e502658094dfda171c78ba78 Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Fri, 17 Mar 2017 19:48:37 +0100
Subject: [PATCH 10/17] Replace RwLock<Keyframe> with Locked<Keyframe>

---
 components/script/dom/bindings/trace.rs   |  2 +-
 components/script/dom/csskeyframerule.rs  | 26 +++++++++++-------
 components/script/dom/csskeyframesrule.rs |  2 +-
 components/style/keyframes.rs             | 33 ++++++++++++++---------
 components/style/stylesheets.rs           |  8 +++---
 components/style/stylist.rs               |  3 ++-
 tests/unit/style/keyframes.rs             | 30 ++++++++++++---------
 tests/unit/style/stylesheets.rs           |  4 +--
 8 files changed, 64 insertions(+), 44 deletions(-)

diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index efa1a5646f2..387709d7332 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -514,7 +514,7 @@ unsafe impl JSTraceable for StyleLocked<CssRules> {
     }
 }
 
-unsafe impl JSTraceable for RwLock<Keyframe> {
+unsafe impl JSTraceable for StyleLocked<Keyframe> {
     unsafe fn trace(&self, _trc: *mut JSTracer) {
         // Do nothing.
     }
diff --git a/components/script/dom/csskeyframerule.rs b/components/script/dom/csskeyframerule.rs
index 0f620bdc764..617546d6a76 100644
--- a/components/script/dom/csskeyframerule.rs
+++ b/components/script/dom/csskeyframerule.rs
@@ -12,21 +12,21 @@ use dom::cssstyledeclaration::{CSSModificationAccess, CSSStyleDeclaration, CSSSt
 use dom::cssstylesheet::CSSStyleSheet;
 use dom::window::Window;
 use dom_struct::dom_struct;
-use parking_lot::RwLock;
 use std::sync::Arc;
 use style::keyframes::Keyframe;
+use style::shared_lock::Locked;
 use style_traits::ToCss;
 
 #[dom_struct]
 pub struct CSSKeyframeRule {
     cssrule: CSSRule,
     #[ignore_heap_size_of = "Arc"]
-    keyframerule: Arc<RwLock<Keyframe>>,
+    keyframerule: Arc<Locked<Keyframe>>,
     style_decl: MutNullableJS<CSSStyleDeclaration>,
 }
 
 impl CSSKeyframeRule {
-    fn new_inherited(parent_stylesheet: &CSSStyleSheet, keyframerule: Arc<RwLock<Keyframe>>)
+    fn new_inherited(parent_stylesheet: &CSSStyleSheet, keyframerule: Arc<Locked<Keyframe>>)
                      -> CSSKeyframeRule {
         CSSKeyframeRule {
             cssrule: CSSRule::new_inherited(parent_stylesheet),
@@ -37,7 +37,7 @@ impl CSSKeyframeRule {
 
     #[allow(unrooted_must_root)]
     pub fn new(window: &Window, parent_stylesheet: &CSSStyleSheet,
-               keyframerule: Arc<RwLock<Keyframe>>) -> Root<CSSKeyframeRule> {
+               keyframerule: Arc<Locked<Keyframe>>) -> Root<CSSKeyframeRule> {
         reflect_dom_object(box CSSKeyframeRule::new_inherited(parent_stylesheet, keyframerule),
                            window,
                            CSSKeyframeRuleBinding::Wrap)
@@ -48,11 +48,16 @@ impl CSSKeyframeRuleMethods for CSSKeyframeRule {
     // https://drafts.csswg.org/css-animations/#dom-csskeyframerule-style
     fn Style(&self) -> Root<CSSStyleDeclaration> {
         self.style_decl.or_init(|| {
-            CSSStyleDeclaration::new(self.global().as_window(),
-                                     CSSStyleOwner::CSSRule(JS::from_ref(self.upcast()),
-                                                            self.keyframerule.read().block.clone()),
-                                     None,
-                                     CSSModificationAccess::ReadWrite)
+            let guard = self.cssrule.shared_lock().read();
+            CSSStyleDeclaration::new(
+                self.global().as_window(),
+                CSSStyleOwner::CSSRule(
+                    JS::from_ref(self.upcast()),
+                    self.keyframerule.read_with(&guard).block.clone(),
+                ),
+                None,
+                CSSModificationAccess::ReadWrite,
+            )
         })
     }
 }
@@ -64,6 +69,7 @@ impl SpecificCSSRule for CSSKeyframeRule {
     }
 
     fn get_css(&self) -> DOMString {
-        self.keyframerule.read().to_css_string().into()
+        let guard = self.cssrule.shared_lock().read();
+        self.keyframerule.read_with(&guard).to_css_string().into()
     }
 }
diff --git a/components/script/dom/csskeyframesrule.rs b/components/script/dom/csskeyframesrule.rs
index d17eeeb51b5..288ae486d1d 100644
--- a/components/script/dom/csskeyframesrule.rs
+++ b/components/script/dom/csskeyframesrule.rs
@@ -67,7 +67,7 @@ impl CSSKeyframesRule {
             // because that's the rule that applies. Thus, rposition
             self.keyframesrule.read_with(&guard)
                 .keyframes.iter().rposition(|frame| {
-                    frame.read().selector == sel
+                    frame.read_with(&guard).selector == sel
                 })
         } else {
             None
diff --git a/components/style/keyframes.rs b/components/style/keyframes.rs
index 69aeb669dcc..44ca0921706 100644
--- a/components/style/keyframes.rs
+++ b/components/style/keyframes.rs
@@ -15,6 +15,7 @@ use properties::{PropertyDeclarationId, LonghandId, ParsedDeclaration};
 use properties::LonghandIdSet;
 use properties::animated_properties::TransitionProperty;
 use properties::longhands::transition_timing_function::single_value::SpecifiedValue as SpecifiedTimingFunction;
+use shared_lock::{SharedRwLock, SharedRwLockReadGuard, Locked};
 use std::fmt;
 use std::sync::Arc;
 use style_traits::ToCss;
@@ -125,7 +126,7 @@ impl Keyframe {
     pub fn parse(css: &str,
                  parent_stylesheet: &Stylesheet,
                  extra_data: ParserContextExtraData)
-                 -> Result<Arc<RwLock<Self>>, ()> {
+                 -> Result<Arc<Locked<Self>>, ()> {
         let error_reporter = MemoryHoleReporter;
         let context = ParserContext::new_with_extra_data(parent_stylesheet.origin,
                                                          &parent_stylesheet.base_url,
@@ -135,6 +136,7 @@ impl Keyframe {
 
         let mut rule_parser = KeyframeListParser {
             context: &context,
+            shared_lock: &parent_stylesheet.shared_lock,
         };
         parse_one_rule(&mut input, &mut rule_parser)
     }
@@ -239,13 +241,14 @@ pub struct KeyframesAnimation {
 }
 
 /// Get all the animated properties in a keyframes animation.
-fn get_animated_properties(keyframes: &[Arc<RwLock<Keyframe>>]) -> Vec<TransitionProperty> {
+fn get_animated_properties(keyframes: &[Arc<Locked<Keyframe>>], guard: &SharedRwLockReadGuard)
+                           -> Vec<TransitionProperty> {
     let mut ret = vec![];
     let mut seen = LonghandIdSet::new();
     // NB: declarations are already deduplicated, so we don't have to check for
     // it here.
     for keyframe in keyframes {
-        let keyframe = keyframe.read();
+        let keyframe = keyframe.read_with(&guard);
         for &(ref declaration, importance) in keyframe.block.read().declarations().iter() {
             assert!(!importance.important());
 
@@ -270,7 +273,8 @@ impl KeyframesAnimation {
     ///
     /// Otherwise, this will compute and sort the steps used for the animation,
     /// and return the animation object.
-    pub fn from_keyframes(keyframes: &[Arc<RwLock<Keyframe>>]) -> Self {
+    pub fn from_keyframes(keyframes: &[Arc<Locked<Keyframe>>], guard: &SharedRwLockReadGuard)
+                          -> Self {
         let mut result = KeyframesAnimation {
             steps: vec![],
             properties_changed: vec![],
@@ -280,13 +284,13 @@ impl KeyframesAnimation {
             return result;
         }
 
-        result.properties_changed = get_animated_properties(keyframes);
+        result.properties_changed = get_animated_properties(keyframes, guard);
         if result.properties_changed.is_empty() {
             return result;
         }
 
         for keyframe in keyframes {
-            let keyframe = keyframe.read();
+            let keyframe = keyframe.read_with(&guard);
             for percentage in keyframe.selector.0.iter() {
                 result.steps.push(KeyframesStep::new(*percentage, KeyframesStepValue::Declarations {
                     block: keyframe.block.clone(),
@@ -322,24 +326,27 @@ impl KeyframesAnimation {
 /// }
 struct KeyframeListParser<'a> {
     context: &'a ParserContext<'a>,
+    shared_lock: &'a SharedRwLock,
 }
 
 /// Parses a keyframe list from CSS input.
-pub fn parse_keyframe_list(context: &ParserContext, input: &mut Parser) -> Vec<Arc<RwLock<Keyframe>>> {
-    RuleListParser::new_for_nested_rule(input, KeyframeListParser { context: context })
-        .filter_map(Result::ok)
-        .collect()
+pub fn parse_keyframe_list(context: &ParserContext, input: &mut Parser, shared_lock: &SharedRwLock)
+                           -> Vec<Arc<Locked<Keyframe>>> {
+    RuleListParser::new_for_nested_rule(input, KeyframeListParser {
+        context: context,
+        shared_lock: shared_lock,
+    }).filter_map(Result::ok).collect()
 }
 
 enum Void {}
 impl<'a> AtRuleParser for KeyframeListParser<'a> {
     type Prelude = Void;
-    type AtRule = Arc<RwLock<Keyframe>>;
+    type AtRule = Arc<Locked<Keyframe>>;
 }
 
 impl<'a> QualifiedRuleParser for KeyframeListParser<'a> {
     type Prelude = KeyframeSelector;
-    type QualifiedRule = Arc<RwLock<Keyframe>>;
+    type QualifiedRule = Arc<Locked<Keyframe>>;
 
     fn parse_prelude(&mut self, input: &mut Parser) -> Result<Self::Prelude, ()> {
         let start = input.position();
@@ -372,7 +379,7 @@ impl<'a> QualifiedRuleParser for KeyframeListParser<'a> {
             }
             // `parse_important` is not called here, `!important` is not allowed in keyframe blocks.
         }
-        Ok(Arc::new(RwLock::new(Keyframe {
+        Ok(Arc::new(self.shared_lock.wrap(Keyframe {
             selector: prelude,
             block: Arc::new(RwLock::new(block)),
         })))
diff --git a/components/style/stylesheets.rs b/components/style/stylesheets.rs
index a0f0baa3840..d132c64bbb9 100644
--- a/components/style/stylesheets.rs
+++ b/components/style/stylesheets.rs
@@ -451,12 +451,12 @@ pub struct KeyframesRule {
     /// The name of the current animation.
     pub name: Atom,
     /// The keyframes specified for this CSS rule.
-    pub keyframes: Vec<Arc<RwLock<Keyframe>>>,
+    pub keyframes: Vec<Arc<Locked<Keyframe>>>,
 }
 
 impl ToCssWithGuard for KeyframesRule {
     // Serialization of KeyframesRule is not specced.
-    fn to_css<W>(&self, _guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
+    fn to_css<W>(&self, guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
     where W: fmt::Write {
         try!(dest.write_str("@keyframes "));
         try!(dest.write_str(&*self.name.to_string()));
@@ -468,7 +468,7 @@ impl ToCssWithGuard for KeyframesRule {
                 try!(dest.write_str(" "));
             }
             first = false;
-            let keyframe = lock.read();
+            let keyframe = lock.read_with(&guard);
             try!(keyframe.to_css(dest));
         }
         dest.write_str(" }")
@@ -1009,7 +1009,7 @@ impl<'a, 'b> AtRuleParser for NestedRuleParser<'a, 'b> {
             AtRulePrelude::Keyframes(name) => {
                 Ok(CssRule::Keyframes(Arc::new(self.shared_lock.wrap(KeyframesRule {
                     name: name,
-                    keyframes: parse_keyframe_list(&self.context, input),
+                    keyframes: parse_keyframe_list(&self.context, input, self.shared_lock),
                 }))))
             }
         }
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index 4e6b6350beb..a110e4f7abb 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -280,7 +280,8 @@ impl Stylist {
                 CssRule::Keyframes(ref keyframes_rule) => {
                     let keyframes_rule = keyframes_rule.read_with(guard);
                     debug!("Found valid keyframes rule: {:?}", *keyframes_rule);
-                    let animation = KeyframesAnimation::from_keyframes(&keyframes_rule.keyframes);
+                    let animation = KeyframesAnimation::from_keyframes(
+                        &keyframes_rule.keyframes, guard);
                     debug!("Found valid keyframe animation: {:?}", animation);
                     self.animations.insert(keyframes_rule.name.clone(), animation);
                 }
diff --git a/tests/unit/style/keyframes.rs b/tests/unit/style/keyframes.rs
index 051ff9ca792..a916f18da01 100644
--- a/tests/unit/style/keyframes.rs
+++ b/tests/unit/style/keyframes.rs
@@ -8,12 +8,14 @@ use style::keyframes::{Keyframe, KeyframesAnimation, KeyframePercentage,  Keyfra
 use style::keyframes::{KeyframesStep, KeyframesStepValue};
 use style::properties::{PropertyDeclaration, PropertyDeclarationBlock, Importance};
 use style::properties::animated_properties::TransitionProperty;
+use style::shared_lock::SharedRwLock;
 use style::values::specified::{LengthOrPercentageOrAuto, NoCalcLength};
 
 #[test]
 fn test_empty_keyframe() {
+    let shared_lock = SharedRwLock::new();
     let keyframes = vec![];
-    let animation = KeyframesAnimation::from_keyframes(&keyframes);
+    let animation = KeyframesAnimation::from_keyframes(&keyframes, &shared_lock.read());
     let expected = KeyframesAnimation {
         steps: vec![],
         properties_changed: vec![],
@@ -24,13 +26,14 @@ fn test_empty_keyframe() {
 
 #[test]
 fn test_no_property_in_keyframe() {
+    let shared_lock = SharedRwLock::new();
     let keyframes = vec![
-        Arc::new(RwLock::new(Keyframe {
+        Arc::new(shared_lock.wrap(Keyframe {
             selector: KeyframeSelector::new_for_unit_testing(vec![KeyframePercentage::new(1.)]),
             block: Arc::new(RwLock::new(PropertyDeclarationBlock::new()))
         })),
     ];
-    let animation = KeyframesAnimation::from_keyframes(&keyframes);
+    let animation = KeyframesAnimation::from_keyframes(&keyframes, &shared_lock.read());
     let expected = KeyframesAnimation {
         steps: vec![],
         properties_changed: vec![],
@@ -41,6 +44,7 @@ fn test_no_property_in_keyframe() {
 
 #[test]
 fn test_missing_property_in_initial_keyframe() {
+    let shared_lock = SharedRwLock::new();
     let declarations_on_initial_keyframe =
         Arc::new(RwLock::new(PropertyDeclarationBlock::with_one(
             PropertyDeclaration::Width(
@@ -65,17 +69,17 @@ fn test_missing_property_in_initial_keyframe() {
         }));
 
     let keyframes = vec![
-        Arc::new(RwLock::new(Keyframe {
+        Arc::new(shared_lock.wrap(Keyframe {
             selector: KeyframeSelector::new_for_unit_testing(vec![KeyframePercentage::new(0.)]),
             block: declarations_on_initial_keyframe.clone(),
         })),
 
-        Arc::new(RwLock::new(Keyframe {
+        Arc::new(shared_lock.wrap(Keyframe {
             selector: KeyframeSelector::new_for_unit_testing(vec![KeyframePercentage::new(1.)]),
             block: declarations_on_final_keyframe.clone(),
         })),
     ];
-    let animation = KeyframesAnimation::from_keyframes(&keyframes);
+    let animation = KeyframesAnimation::from_keyframes(&keyframes, &shared_lock.read());
     let expected = KeyframesAnimation {
         steps: vec![
             KeyframesStep {
@@ -97,6 +101,7 @@ fn test_missing_property_in_initial_keyframe() {
 
 #[test]
 fn test_missing_property_in_final_keyframe() {
+    let shared_lock = SharedRwLock::new();
     let declarations_on_initial_keyframe =
         Arc::new(RwLock::new({
             let mut block = PropertyDeclarationBlock::new();
@@ -121,17 +126,17 @@ fn test_missing_property_in_final_keyframe() {
         )));
 
     let keyframes = vec![
-        Arc::new(RwLock::new(Keyframe {
+        Arc::new(shared_lock.wrap(Keyframe {
             selector: KeyframeSelector::new_for_unit_testing(vec![KeyframePercentage::new(0.)]),
             block: declarations_on_initial_keyframe.clone(),
         })),
 
-        Arc::new(RwLock::new(Keyframe {
+        Arc::new(shared_lock.wrap(Keyframe {
             selector: KeyframeSelector::new_for_unit_testing(vec![KeyframePercentage::new(1.)]),
             block: declarations_on_final_keyframe.clone(),
         })),
     ];
-    let animation = KeyframesAnimation::from_keyframes(&keyframes);
+    let animation = KeyframesAnimation::from_keyframes(&keyframes, &shared_lock.read());
     let expected = KeyframesAnimation {
         steps: vec![
             KeyframesStep {
@@ -153,6 +158,7 @@ fn test_missing_property_in_final_keyframe() {
 
 #[test]
 fn test_missing_keyframe_in_both_of_initial_and_final_keyframe() {
+    let shared_lock = SharedRwLock::new();
     let declarations =
         Arc::new(RwLock::new({
             let mut block = PropertyDeclarationBlock::new();
@@ -170,16 +176,16 @@ fn test_missing_keyframe_in_both_of_initial_and_final_keyframe() {
         }));
 
     let keyframes = vec![
-        Arc::new(RwLock::new(Keyframe {
+        Arc::new(shared_lock.wrap(Keyframe {
             selector: KeyframeSelector::new_for_unit_testing(vec![KeyframePercentage::new(0.)]),
             block: Arc::new(RwLock::new(PropertyDeclarationBlock::new()))
         })),
-        Arc::new(RwLock::new(Keyframe {
+        Arc::new(shared_lock.wrap(Keyframe {
             selector: KeyframeSelector::new_for_unit_testing(vec![KeyframePercentage::new(0.5)]),
             block: declarations.clone(),
         })),
     ];
-    let animation = KeyframesAnimation::from_keyframes(&keyframes);
+    let animation = KeyframesAnimation::from_keyframes(&keyframes, &shared_lock.read());
     let expected = KeyframesAnimation {
         steps: vec![
             KeyframesStep {
diff --git a/tests/unit/style/stylesheets.rs b/tests/unit/style/stylesheets.rs
index a1c67932b53..99ec3676236 100644
--- a/tests/unit/style/stylesheets.rs
+++ b/tests/unit/style/stylesheets.rs
@@ -238,7 +238,7 @@ fn test_parse_stylesheet() {
             CssRule::Keyframes(Arc::new(stylesheet.shared_lock.wrap(KeyframesRule {
                 name: "foo".into(),
                 keyframes: vec![
-                    Arc::new(RwLock::new(Keyframe {
+                    Arc::new(stylesheet.shared_lock.wrap(Keyframe {
                         selector: KeyframeSelector::new_for_unit_testing(
                                       vec![KeyframePercentage::new(0.)]),
                         block: Arc::new(RwLock::new(block_from(vec![
@@ -247,7 +247,7 @@ fn test_parse_stylesheet() {
                              Importance::Normal),
                         ])))
                     })),
-                    Arc::new(RwLock::new(Keyframe {
+                    Arc::new(stylesheet.shared_lock.wrap(Keyframe {
                         selector: KeyframeSelector::new_for_unit_testing(
                                       vec![KeyframePercentage::new(1.)]),
                         block: Arc::new(RwLock::new(block_from(vec![

From aeffca2a5900ebcf91063e9c7771b642817cb6bd Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Sat, 18 Mar 2017 00:47:08 +0100
Subject: [PATCH 11/17] Replace RwLock<StyleRule> with Locked<StyleRule>

---
 Cargo.lock                                    |  2 -
 components/layout/block.rs                    |  2 +-
 components/layout/construct.rs                | 27 +++---
 components/layout/context.rs                  |  8 +-
 components/layout/display_list_builder.rs     |  2 +-
 components/layout/generated_content.rs        |  2 +-
 components/layout/traversal.rs                | 24 ++---
 components/layout_thread/lib.rs               | 42 ++++++---
 components/script/dom/bindings/trace.rs       |  2 +-
 components/script/dom/cssstylerule.rs         | 26 +++---
 components/script/dom/document.rs             |  3 +-
 .../script_layout_interface/wrapper_traits.rs |  2 +
 components/style/Cargo.toml                   |  1 -
 components/style/context.rs                   | 10 ++-
 components/style/gecko/arc_types.rs           | 13 +--
 components/style/gecko/data.rs                |  4 +-
 components/style/gecko/traversal.rs           | 13 +--
 components/style/lib.rs                       |  2 -
 components/style/matching.rs                  |  3 +
 components/style/owning_handle.rs             | 89 -------------------
 .../style/properties/properties.mako.rs       |  9 +-
 components/style/rule_tree/mod.rs             | 81 ++++++++---------
 components/style/servo/mod.rs                 | 10 +++
 components/style/shared_lock.rs               | 20 +++++
 components/style/stylesheets.rs               | 18 +---
 components/style/stylist.rs                   | 62 ++++++++-----
 components/style/traversal.rs                 |  3 +-
 ports/geckolib/glue.rs                        | 50 +++++++----
 tests/unit/style/Cargo.toml                   |  1 -
 tests/unit/style/lib.rs                       |  2 -
 tests/unit/style/owning_handle.rs             | 34 -------
 tests/unit/style/stylesheets.rs               |  6 +-
 tests/unit/style/stylist.rs                   | 40 +++++----
 33 files changed, 279 insertions(+), 334 deletions(-)
 delete mode 100644 components/style/owning_handle.rs
 delete mode 100644 tests/unit/style/owning_handle.rs

diff --git a/Cargo.lock b/Cargo.lock
index d8bf220c648..076924c397c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2757,7 +2757,6 @@ dependencies = [
  "num-integer 0.1.33 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
  "ordered-float 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "owning_ref 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "pdqsort 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "rayon 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2783,7 +2782,6 @@ dependencies = [
  "cssparser 0.12.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "html5ever-atoms 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "owning_ref 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "rayon 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-serialize 0.3.23 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/components/layout/block.rs b/components/layout/block.rs
index 4bfef78cb3d..31f44f0ec0e 100644
--- a/components/layout/block.rs
+++ b/components/layout/block.rs
@@ -446,7 +446,7 @@ fn translate_including_floats(cur_b: &mut Au, delta: Au, floats: &mut Floats) {
 ///
 /// Note that flows with position 'fixed' just form a flat list as they all
 /// have the Root flow as their CB.
-pub struct AbsoluteAssignBSizesTraversal<'a>(pub &'a SharedStyleContext);
+pub struct AbsoluteAssignBSizesTraversal<'a>(pub &'a SharedStyleContext<'a>);
 
 impl<'a> PreorderFlowTraversal for AbsoluteAssignBSizesTraversal<'a> {
     #[inline]
diff --git a/components/layout/construct.rs b/components/layout/construct.rs
index a6571d0e093..00cd46a079a 100644
--- a/components/layout/construct.rs
+++ b/components/layout/construct.rs
@@ -311,7 +311,7 @@ impl InlineFragmentsAccumulator {
 /// An object that knows how to create flows.
 pub struct FlowConstructor<'a, N: ThreadSafeLayoutNode> {
     /// The layout context.
-    pub layout_context: &'a LayoutContext,
+    pub layout_context: &'a LayoutContext<'a>,
     /// Satisfy the compiler about the unused parameters, which we use to improve the ergonomics of
     /// the ensuing impl {} by removing the need to parameterize all the methods individually.
     phantom2: PhantomData<N>,
@@ -320,7 +320,7 @@ pub struct FlowConstructor<'a, N: ThreadSafeLayoutNode> {
 impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
   FlowConstructor<'a, ConcreteThreadSafeLayoutNode> {
     /// Creates a new flow constructor.
-    pub fn new(layout_context: &'a LayoutContext) -> Self {
+    pub fn new(layout_context: &'a LayoutContext<'a>) -> Self {
         FlowConstructor {
             layout_context: layout_context,
             phantom2: PhantomData,
@@ -660,10 +660,9 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
 
             let mut style = node.style(self.style_context());
             if node_is_input_or_text_area {
-                style = self.style_context()
-                            .stylist
-                            .style_for_anonymous_box(&PseudoElement::ServoInputText,
-                                                     &style)
+                let context = self.style_context();
+                style = context.stylist.style_for_anonymous_box(
+                    &context.guards, &PseudoElement::ServoInputText, &style)
             }
 
             self.create_fragments_for_node_text_content(&mut initial_fragments, node, &style)
@@ -1096,11 +1095,14 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
                             -> ConstructionResult {
         let mut legalizer = Legalizer::new();
 
-        let table_style = node.style(self.style_context());
-        let wrapper_style = self.style_context()
-                                .stylist
-                                .style_for_anonymous_box(&PseudoElement::ServoTableWrapper,
-                                                         &table_style);
+        let table_style;
+        let wrapper_style;
+        {
+            let context = self.style_context();
+            table_style = node.style(context);
+            wrapper_style = context.stylist.style_for_anonymous_box(
+                &context.guards, &PseudoElement::ServoTableWrapper, &table_style);
+        }
         let wrapper_fragment =
             Fragment::from_opaque_node_and_style(node.opaque(),
                                                  PseudoElementType::Normal,
@@ -2080,8 +2082,7 @@ impl Legalizer {
         let reference_block = reference.as_block();
         let mut new_style = reference_block.fragment.style.clone();
         for pseudo in pseudos {
-            new_style = context.stylist.style_for_anonymous_box(pseudo,
-                                                                &new_style)
+            new_style = context.stylist.style_for_anonymous_box(&context.guards, pseudo, &new_style)
         }
         let fragment = reference_block.fragment
                                       .create_similar_anonymous_fragment(new_style,
diff --git a/components/layout/context.rs b/components/layout/context.rs
index 1dff9f6ea5e..e2ffeb1cbd9 100644
--- a/components/layout/context.rs
+++ b/components/layout/context.rs
@@ -75,9 +75,9 @@ pub fn heap_size_of_persistent_local_context() -> usize {
 }
 
 /// Layout information shared among all workers. This must be thread-safe.
-pub struct LayoutContext {
+pub struct LayoutContext<'a> {
     /// Bits shared by the layout and style system.
-    pub style_context: SharedStyleContext,
+    pub style_context: SharedStyleContext<'a>,
 
     /// The shared image cache thread.
     pub image_cache_thread: Mutex<ImageCacheThread>,
@@ -95,7 +95,7 @@ pub struct LayoutContext {
     pub pending_images: Option<Mutex<Vec<PendingImage>>>
 }
 
-impl Drop for LayoutContext {
+impl<'a> Drop for LayoutContext<'a> {
     fn drop(&mut self) {
         if !thread::panicking() {
             if let Some(ref pending_images) = self.pending_images {
@@ -105,7 +105,7 @@ impl Drop for LayoutContext {
     }
 }
 
-impl LayoutContext {
+impl<'a> LayoutContext<'a> {
     #[inline(always)]
     pub fn shared_context(&self) -> &SharedStyleContext {
         &self.style_context
diff --git a/components/layout/display_list_builder.rs b/components/layout/display_list_builder.rs
index ab3636fdbc5..2ee9985cf0e 100644
--- a/components/layout/display_list_builder.rs
+++ b/components/layout/display_list_builder.rs
@@ -121,7 +121,7 @@ fn get_cyclic<T>(arr: &[T], index: usize) -> &T {
 }
 
 pub struct DisplayListBuildState<'a> {
-    pub layout_context: &'a LayoutContext,
+    pub layout_context: &'a LayoutContext<'a>,
     pub root_stacking_context: StackingContext,
     pub items: HashMap<StackingContextId, Vec<DisplayItem>>,
     pub stacking_context_children: HashMap<StackingContextId, Vec<StackingContext>>,
diff --git a/components/layout/generated_content.rs b/components/layout/generated_content.rs
index ef2e270c064..887562e89fb 100644
--- a/components/layout/generated_content.rs
+++ b/components/layout/generated_content.rs
@@ -97,7 +97,7 @@ static KATAKANA_IROHA: [char; 47] = [
 /// The generated content resolution traversal.
 pub struct ResolveGeneratedContent<'a> {
     /// The layout context.
-    layout_context: &'a LayoutContext,
+    layout_context: &'a LayoutContext<'a>,
     /// The counter representing an ordered list item.
     list_item: Counter,
     /// Named CSS counters.
diff --git a/components/layout/traversal.rs b/components/layout/traversal.rs
index 0088ef208f3..3c0c1763d0c 100644
--- a/components/layout/traversal.rs
+++ b/components/layout/traversal.rs
@@ -22,20 +22,20 @@ use style::traversal::PerLevelTraversalData;
 use wrapper::{GetRawData, LayoutNodeHelpers, LayoutNodeLayoutData};
 use wrapper::ThreadSafeLayoutNodeHelpers;
 
-pub struct RecalcStyleAndConstructFlows {
-    context: LayoutContext,
+pub struct RecalcStyleAndConstructFlows<'a> {
+    context: LayoutContext<'a>,
     driver: TraversalDriver,
 }
 
-impl RecalcStyleAndConstructFlows {
-    pub fn layout_context(&self) -> &LayoutContext {
+impl<'a> RecalcStyleAndConstructFlows<'a> {
+    pub fn layout_context(&self) -> &LayoutContext<'a> {
         &self.context
     }
 }
 
-impl RecalcStyleAndConstructFlows {
+impl<'a> RecalcStyleAndConstructFlows<'a> {
     /// Creates a traversal context, taking ownership of the shared layout context.
-    pub fn new(context: LayoutContext, driver: TraversalDriver) -> Self {
+    pub fn new(context: LayoutContext<'a>, driver: TraversalDriver) -> Self {
         RecalcStyleAndConstructFlows {
             context: context,
             driver: driver,
@@ -44,13 +44,13 @@ impl RecalcStyleAndConstructFlows {
 
     /// Consumes this traversal context, returning ownership of the shared layout
     /// context to the caller.
-    pub fn destroy(self) -> LayoutContext {
+    pub fn destroy(self) -> LayoutContext<'a> {
         self.context
     }
 }
 
 #[allow(unsafe_code)]
-impl<E> DomTraversal<E> for RecalcStyleAndConstructFlows
+impl<'a, E> DomTraversal<E> for RecalcStyleAndConstructFlows<'a>
     where E: TElement,
           E::ConcreteNode: LayoutNode,
 {
@@ -152,7 +152,7 @@ fn construct_flows_at<N>(context: &LayoutContext,
 /// The bubble-inline-sizes traversal, the first part of layout computation. This computes
 /// preferred and intrinsic inline-sizes and bubbles them up the tree.
 pub struct BubbleISizes<'a> {
-    pub layout_context: &'a LayoutContext,
+    pub layout_context: &'a LayoutContext<'a>,
 }
 
 impl<'a> PostorderFlowTraversal for BubbleISizes<'a> {
@@ -171,7 +171,7 @@ impl<'a> PostorderFlowTraversal for BubbleISizes<'a> {
 /// The assign-inline-sizes traversal. In Gecko this corresponds to `Reflow`.
 #[derive(Copy, Clone)]
 pub struct AssignISizes<'a> {
-    pub layout_context: &'a LayoutContext,
+    pub layout_context: &'a LayoutContext<'a>,
 }
 
 impl<'a> PreorderFlowTraversal for AssignISizes<'a> {
@@ -191,7 +191,7 @@ impl<'a> PreorderFlowTraversal for AssignISizes<'a> {
 /// positions. In Gecko this corresponds to `Reflow`.
 #[derive(Copy, Clone)]
 pub struct AssignBSizes<'a> {
-    pub layout_context: &'a LayoutContext,
+    pub layout_context: &'a LayoutContext<'a>,
 }
 
 impl<'a> PostorderFlowTraversal for AssignBSizes<'a> {
@@ -220,7 +220,7 @@ impl<'a> PostorderFlowTraversal for AssignBSizes<'a> {
 
 #[derive(Copy, Clone)]
 pub struct ComputeAbsolutePositions<'a> {
-    pub layout_context: &'a LayoutContext,
+    pub layout_context: &'a LayoutContext<'a>,
 }
 
 impl<'a> PreorderFlowTraversal for ComputeAbsolutePositions<'a> {
diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index 566d6c7ca33..32708911484 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -114,8 +114,9 @@ use style::error_reporting::StdoutErrorReporter;
 use style::logical_geometry::LogicalPoint;
 use style::media_queries::{Device, MediaType};
 use style::parser::ParserContextExtraData;
+use style::servo::AUTHOR_SHARED_LOCK;
 use style::servo::restyle_damage::{REFLOW, REFLOW_OUT_OF_FLOW, REPAINT, REPOSITION, STORE_OVERFLOW};
-use style::shared_lock::{SharedRwLock, SharedRwLockReadGuard};
+use style::shared_lock::{SharedRwLock, SharedRwLockReadGuard, ReadGuards};
 use style::stylesheets::{Origin, Stylesheet, UserAgentStylesheets};
 use style::stylist::Stylist;
 use style::thread_state;
@@ -215,7 +216,7 @@ pub struct LayoutThread {
                                               WebRenderImageInfo,
                                               BuildHasherDefault<FnvHasher>>>>,
 
-    // Webrender interface.
+    /// Webrender interface.
     webrender_api: webrender_traits::RenderApi,
 
     /// The timer object to control the timing of the animations. This should
@@ -498,16 +499,18 @@ impl LayoutThread {
     }
 
     // Create a layout context for use in building display lists, hit testing, &c.
-    fn build_layout_context(&self,
-                            rw_data: &LayoutThreadData,
-                            request_images: bool)
-                            -> LayoutContext {
+    fn build_layout_context<'a>(&self,
+                                guards: ReadGuards<'a>,
+                                rw_data: &LayoutThreadData,
+                                request_images: bool)
+                                -> LayoutContext<'a> {
         let thread_local_style_context_creation_data =
             ThreadLocalStyleContextCreationInfo::new(self.new_animations_sender.clone());
 
         LayoutContext {
             style_context: SharedStyleContext {
                 stylist: rw_data.stylist.clone(),
+                guards: guards,
                 running_animations: self.running_animations.clone(),
                 expired_animations: self.expired_animations.clone(),
                 error_reporter: Box::new(self.error_reporter.clone()),
@@ -941,7 +944,6 @@ impl LayoutThread {
                              possibly_locked_rw_data: &mut RwData<'a, 'b>) {
         let document = unsafe { ServoLayoutNode::new(&data.document) };
         let document = document.as_document().unwrap();
-        let style_guard = document.style_shared_lock().read();
         self.quirks_mode = Some(document.quirks_mode());
 
         // FIXME(pcwalton): Combine `ReflowGoal` and `ReflowQueryType`. Then remove this assert.
@@ -1017,9 +1019,11 @@ impl LayoutThread {
                                               Au::from_f32_px(initial_viewport.height));
 
         // Calculate the actual viewport as per DEVICE-ADAPT § 6
+
+        let author_guard = document.style_shared_lock().read();
         let device = Device::new(MediaType::Screen, initial_viewport);
         Arc::get_mut(&mut rw_data.stylist).unwrap()
-            .set_device(device, &style_guard, &data.document_stylesheets);
+            .set_device(device, &author_guard, &data.document_stylesheets);
 
         self.viewport_size =
             rw_data.stylist.viewport_constraints().map_or(current_screen_size, |constraints| {
@@ -1063,10 +1067,16 @@ impl LayoutThread {
         }
 
         // If the entire flow tree is invalid, then it will be reflowed anyhow.
+        let ua_stylesheets = &*UA_STYLESHEETS;
+        let ua_or_user_guard = ua_stylesheets.shared_lock.read();
+        let guards = ReadGuards {
+            author: &author_guard,
+            ua_or_user: &ua_or_user_guard,
+        };
         let needs_dirtying = Arc::get_mut(&mut rw_data.stylist).unwrap().update(
             &data.document_stylesheets,
-            &style_guard,
-            Some(&*UA_STYLESHEETS),
+            &guards,
+            Some(ua_stylesheets),
             data.stylesheets_changed);
         let needs_reflow = viewport_size_changed && !needs_dirtying;
         if needs_dirtying {
@@ -1113,7 +1123,7 @@ impl LayoutThread {
         }
 
         // Create a layout context for use throughout the following passes.
-        let mut layout_context = self.build_layout_context(&*rw_data, true);
+        let mut layout_context = self.build_layout_context(guards.clone(), &*rw_data, true);
 
         // NB: Type inference falls apart here for some reason, so we need to be very verbose. :-(
         let traversal_driver = if self.parallel_flag && self.parallel_traversal.is_some() {
@@ -1172,7 +1182,7 @@ impl LayoutThread {
         }
 
         if opts::get().dump_rule_tree {
-            layout_context.style_context.stylist.rule_tree.dump_stdout();
+            layout_context.style_context.stylist.rule_tree.dump_stdout(&guards);
         }
 
         // GC the rule tree if some heuristics are met.
@@ -1341,7 +1351,13 @@ impl LayoutThread {
             page_clip_rect: max_rect(),
         };
 
-        let mut layout_context = self.build_layout_context(&*rw_data, false);
+        let author_guard = AUTHOR_SHARED_LOCK.read();
+        let ua_or_user_guard = UA_STYLESHEETS.shared_lock.read();
+        let guards = ReadGuards {
+            author: &author_guard,
+            ua_or_user: &ua_or_user_guard,
+        };
+        let mut layout_context = self.build_layout_context(guards, &*rw_data, false);
 
         if let Some(mut root_flow) = self.root_flow.clone() {
             // Perform an abbreviated style recalc that operates without access to the DOM.
diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index 387709d7332..7cad9f98523 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -550,7 +550,7 @@ unsafe impl JSTraceable for StyleLocked<NamespaceRule> {
     }
 }
 
-unsafe impl JSTraceable for RwLock<StyleRule> {
+unsafe impl JSTraceable for StyleLocked<StyleRule> {
     unsafe fn trace(&self, _trc: *mut JSTracer) {
         // Do nothing.
     }
diff --git a/components/script/dom/cssstylerule.rs b/components/script/dom/cssstylerule.rs
index 2423861e446..fed2b947f90 100644
--- a/components/script/dom/cssstylerule.rs
+++ b/components/script/dom/cssstylerule.rs
@@ -12,21 +12,20 @@ use dom::cssstyledeclaration::{CSSModificationAccess, CSSStyleDeclaration, CSSSt
 use dom::cssstylesheet::CSSStyleSheet;
 use dom::window::Window;
 use dom_struct::dom_struct;
-use parking_lot::RwLock;
 use std::sync::Arc;
-use style::shared_lock::ToCssWithGuard;
+use style::shared_lock::{Locked, ToCssWithGuard};
 use style::stylesheets::StyleRule;
 
 #[dom_struct]
 pub struct CSSStyleRule {
     cssrule: CSSRule,
     #[ignore_heap_size_of = "Arc"]
-    stylerule: Arc<RwLock<StyleRule>>,
+    stylerule: Arc<Locked<StyleRule>>,
     style_decl: MutNullableJS<CSSStyleDeclaration>,
 }
 
 impl CSSStyleRule {
-    fn new_inherited(parent_stylesheet: &CSSStyleSheet, stylerule: Arc<RwLock<StyleRule>>)
+    fn new_inherited(parent_stylesheet: &CSSStyleSheet, stylerule: Arc<Locked<StyleRule>>)
                      -> CSSStyleRule {
         CSSStyleRule {
             cssrule: CSSRule::new_inherited(parent_stylesheet),
@@ -37,7 +36,7 @@ impl CSSStyleRule {
 
     #[allow(unrooted_must_root)]
     pub fn new(window: &Window, parent_stylesheet: &CSSStyleSheet,
-               stylerule: Arc<RwLock<StyleRule>>) -> Root<CSSStyleRule> {
+               stylerule: Arc<Locked<StyleRule>>) -> Root<CSSStyleRule> {
         reflect_dom_object(box CSSStyleRule::new_inherited(parent_stylesheet, stylerule),
                            window,
                            CSSStyleRuleBinding::Wrap)
@@ -52,7 +51,7 @@ impl SpecificCSSRule for CSSStyleRule {
 
     fn get_css(&self) -> DOMString {
         let guard = self.cssrule.shared_lock().read();
-        self.stylerule.read().to_css_string(&guard).into()
+        self.stylerule.read_with(&guard).to_css_string(&guard).into()
     }
 }
 
@@ -60,11 +59,16 @@ impl CSSStyleRuleMethods for CSSStyleRule {
     // https://drafts.csswg.org/cssom/#dom-cssstylerule-style
     fn Style(&self) -> Root<CSSStyleDeclaration> {
         self.style_decl.or_init(|| {
-            CSSStyleDeclaration::new(self.global().as_window(),
-                                     CSSStyleOwner::CSSRule(JS::from_ref(self.upcast()),
-                                                            self.stylerule.read().block.clone()),
-                                     None,
-                                     CSSModificationAccess::ReadWrite)
+            let guard = self.cssrule.shared_lock().read();
+            CSSStyleDeclaration::new(
+                self.global().as_window(),
+                CSSStyleOwner::CSSRule(
+                    JS::from_ref(self.upcast()),
+                    self.stylerule.read_with(&guard).block.clone()
+                ),
+                None,
+                CSSModificationAccess::ReadWrite
+            )
         })
     }
 }
diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index 7a50fe5cf6c..b875c75d837 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -134,6 +134,7 @@ use style::attr::AttrValue;
 use style::context::{QuirksMode, ReflowGoal};
 use style::restyle_hints::{RestyleHint, RESTYLE_STYLE_ATTRIBUTE};
 use style::selector_parser::{RestyleDamage, Snapshot};
+use style::servo::AUTHOR_SHARED_LOCK;
 use style::shared_lock::SharedRwLock as StyleSharedRwLock;
 use style::str::{HTML_SPACE_CHARACTERS, split_html_space_chars, str_join};
 use style::stylesheets::Stylesheet;
@@ -2131,7 +2132,7 @@ impl Document {
             scripts: Default::default(),
             anchors: Default::default(),
             applets: Default::default(),
-            style_shared_lock: StyleSharedRwLock::new(),
+            style_shared_lock: AUTHOR_SHARED_LOCK.clone(),
             stylesheets: DOMRefCell::new(None),
             stylesheets_changed_since_reflow: Cell::new(false),
             stylesheet_list: MutNullableJS::new(None),
diff --git a/components/script_layout_interface/wrapper_traits.rs b/components/script_layout_interface/wrapper_traits.rs
index 0e7cb160334..86e293d4a05 100644
--- a/components/script_layout_interface/wrapper_traits.rs
+++ b/components/script_layout_interface/wrapper_traits.rs
@@ -405,6 +405,7 @@ pub trait ThreadSafeLayoutElement: Clone + Copy + Sized + Debug +
                             let mut data = self.get_style_data().unwrap().borrow_mut();
                             let new_style =
                                 context.stylist.precomputed_values_for_pseudo(
+                                    &context.guards,
                                     &style_pseudo,
                                     Some(data.styles().primary.values()),
                                     CascadeFlags::empty());
@@ -421,6 +422,7 @@ pub trait ThreadSafeLayoutElement: Clone + Copy + Sized + Debug +
                             let new_style =
                                 context.stylist
                                        .lazily_compute_pseudo_element_style(
+                                           &context.guards,
                                            unsafe { &self.unsafe_get() },
                                            &style_pseudo,
                                            data.styles().primary.values());
diff --git a/components/style/Cargo.toml b/components/style/Cargo.toml
index a4a6e5ac823..c1c234c994a 100644
--- a/components/style/Cargo.toml
+++ b/components/style/Cargo.toml
@@ -40,7 +40,6 @@ nsstring_vendor = {path = "gecko_bindings/nsstring_vendor", optional = true}
 num-integer = "0.1.32"
 num-traits = "0.1.32"
 ordered-float = "0.4"
-owning_ref = "0.2.2"
 parking_lot = "0.3.3"
 pdqsort = "0.1.0"
 rayon = "0.6"
diff --git a/components/style/context.rs b/components/style/context.rs
index 44485915c2c..93dfde0932b 100644
--- a/components/style/context.rs
+++ b/components/style/context.rs
@@ -17,6 +17,7 @@ use parking_lot::RwLock;
 use selector_parser::PseudoElement;
 use selectors::matching::ElementSelectorFlags;
 use servo_config::opts;
+use shared_lock::ReadGuards;
 use std::collections::HashMap;
 use std::env;
 use std::fmt;
@@ -61,10 +62,13 @@ pub enum QuirksMode {
 ///
 /// There's exactly one of these during a given restyle traversal, and it's
 /// shared among the worker threads.
-pub struct SharedStyleContext {
+pub struct SharedStyleContext<'a> {
     /// The CSS selector stylist.
     pub stylist: Arc<Stylist>,
 
+    /// Guards for pre-acquired locks
+    pub guards: ReadGuards<'a>,
+
     /// The animations that are currently running.
     pub running_animations: Arc<RwLock<HashMap<OpaqueNode, Vec<Animation>>>>,
 
@@ -85,7 +89,7 @@ pub struct SharedStyleContext {
     pub quirks_mode: QuirksMode,
 }
 
-impl SharedStyleContext {
+impl<'a> SharedStyleContext<'a> {
     /// Return a suitable viewport size in order to be used for viewport units.
     pub fn viewport_size(&self) -> Size2D<Au> {
         self.stylist.device.au_viewport_size()
@@ -306,7 +310,7 @@ impl<E: TElement> Drop for ThreadLocalStyleContext<E> {
 /// shared style context, and a mutable reference to a local one.
 pub struct StyleContext<'a, E: TElement + 'a> {
     /// The shared style context reference.
-    pub shared: &'a SharedStyleContext,
+    pub shared: &'a SharedStyleContext<'a>,
     /// The thread-local style context (mutable) reference.
     pub thread_local: &'a mut ThreadLocalStyleContext<E>,
 }
diff --git a/components/style/gecko/arc_types.rs b/components/style/gecko/arc_types.rs
index 58ec43cf387..d400c01c568 100644
--- a/components/style/gecko/arc_types.rs
+++ b/components/style/gecko/arc_types.rs
@@ -51,18 +51,7 @@ impl_arc_ffi!(ComputedValues => ServoComputedValues
 impl_arc_ffi!(RwLock<PropertyDeclarationBlock> => RawServoDeclarationBlock
               [Servo_DeclarationBlock_AddRef, Servo_DeclarationBlock_Release]);
 
-/// FIXME: Remove once StyleRule is actually in Locked<_>
-pub trait HackHackHack {
-    fn as_arc<'a>(ptr: &'a &RawServoStyleRule) -> &'a ::std::sync::Arc<RwLock<StyleRule>>;
-}
-
-impl HackHackHack for Locked<StyleRule> {
-    fn as_arc<'a>(ptr: &'a &RawServoStyleRule) -> &'a ::std::sync::Arc<RwLock<StyleRule>> {
-        RwLock::<StyleRule>::as_arc(ptr)
-    }
-}
-
-impl_arc_ffi!(RwLock<StyleRule> => RawServoStyleRule
+impl_arc_ffi!(Locked<StyleRule> => RawServoStyleRule
               [Servo_StyleRule_AddRef, Servo_StyleRule_Release]);
 
 impl_arc_ffi!(Locked<ImportRule> => RawServoImportRule
diff --git a/components/style/gecko/data.rs b/components/style/gecko/data.rs
index e0f7df023e2..ad6a1d1629c 100644
--- a/components/style/gecko/data.rs
+++ b/components/style/gecko/data.rs
@@ -13,7 +13,7 @@ use gecko_bindings::sugar::ownership::{HasBoxFFI, HasFFI, HasSimpleFFI};
 use media_queries::Device;
 use parking_lot::RwLock;
 use properties::ComputedValues;
-use shared_lock::SharedRwLockReadGuard;
+use shared_lock::{ReadGuards, SharedRwLockReadGuard};
 use std::collections::HashMap;
 use std::sync::Arc;
 use std::sync::mpsc::{Receiver, Sender, channel};
@@ -97,7 +97,7 @@ impl PerDocumentStyleDataImpl {
     pub fn flush_stylesheets(&mut self, guard: &SharedRwLockReadGuard) {
         if self.stylesheets_changed {
             let mut stylist = Arc::get_mut(&mut self.stylist).unwrap();
-            stylist.update(&self.stylesheets, guard, None, true);
+            stylist.update(&self.stylesheets, &ReadGuards::same(guard), None, true);
             self.stylesheets_changed = false;
         }
     }
diff --git a/components/style/gecko/traversal.rs b/components/style/gecko/traversal.rs
index 3cb7f30cb1b..7a68f66c75f 100644
--- a/components/style/gecko/traversal.rs
+++ b/components/style/gecko/traversal.rs
@@ -13,14 +13,14 @@ use traversal::{DomTraversal, PerLevelTraversalData, TraversalDriver, recalc_sty
 
 /// This is the simple struct that Gecko uses to encapsulate a DOM traversal for
 /// styling.
-pub struct RecalcStyleOnly {
-    shared: SharedStyleContext,
+pub struct RecalcStyleOnly<'a> {
+    shared: SharedStyleContext<'a>,
     driver: TraversalDriver,
 }
 
-impl RecalcStyleOnly {
+impl<'a> RecalcStyleOnly<'a> {
     /// Create a `RecalcStyleOnly` traversal from a `SharedStyleContext`.
-    pub fn new(shared: SharedStyleContext, driver: TraversalDriver) -> Self {
+    pub fn new(shared: SharedStyleContext<'a>, driver: TraversalDriver) -> Self {
         RecalcStyleOnly {
             shared: shared,
             driver: driver,
@@ -28,10 +28,11 @@ impl RecalcStyleOnly {
     }
 }
 
-impl<'le> DomTraversal<GeckoElement<'le>> for RecalcStyleOnly {
+impl<'recalc, 'le> DomTraversal<GeckoElement<'le>> for RecalcStyleOnly<'recalc> {
     type ThreadLocalContext = ThreadLocalStyleContext<GeckoElement<'le>>;
 
-    fn process_preorder(&self, traversal_data: &mut PerLevelTraversalData,
+    fn process_preorder(&self,
+                        traversal_data: &mut PerLevelTraversalData,
                         thread_local: &mut Self::ThreadLocalContext,
                         node: GeckoNode<'le>)
     {
diff --git a/components/style/lib.rs b/components/style/lib.rs
index 58dcafe9ceb..eabb8d20c51 100644
--- a/components/style/lib.rs
+++ b/components/style/lib.rs
@@ -60,7 +60,6 @@ extern crate matches;
 extern crate num_integer;
 extern crate num_traits;
 extern crate ordered_float;
-extern crate owning_ref;
 extern crate parking_lot;
 extern crate pdqsort;
 extern crate rayon;
@@ -99,7 +98,6 @@ pub mod keyframes;
 pub mod logical_geometry;
 pub mod matching;
 pub mod media_queries;
-pub mod owning_handle;
 pub mod parallel;
 pub mod parser;
 pub mod restyle_hints;
diff --git a/components/style/matching.rs b/components/style/matching.rs
index 296862cfe20..f58d429beb0 100644
--- a/components/style/matching.rs
+++ b/components/style/matching.rs
@@ -541,6 +541,7 @@ trait PrivateMatchMethods: TElement {
         let values =
             Arc::new(cascade(&shared_context.stylist.device,
                              rule_node,
+                             &shared_context.guards,
                              inherited_values,
                              layout_parent_style,
                              Some(&mut cascade_info),
@@ -784,6 +785,7 @@ pub trait MatchMethods : TElement {
                                                  style_attribute,
                                                  animation_rules,
                                                  None,
+                                                 &context.shared.guards,
                                                  &mut applicable_declarations,
                                                  &mut flags);
         let primary_rule_node = compute_rule_node(context, &mut applicable_declarations);
@@ -809,6 +811,7 @@ pub trait MatchMethods : TElement {
                                                  Some(context.thread_local.bloom_filter.filter()),
                                                  None, pseudo_animation_rules,
                                                  Some(&pseudo),
+                                                 &context.shared.guards,
                                                  &mut applicable_declarations,
                                                  &mut flags);
 
diff --git a/components/style/owning_handle.rs b/components/style/owning_handle.rs
deleted file mode 100644
index 1294bf7e59f..00000000000
--- a/components/style/owning_handle.rs
+++ /dev/null
@@ -1,89 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#![allow(unsafe_code)]
-#![deny(missing_docs)]
-
-//! A handle that encapsulate a reference to a given data along with its owner.
-
-use owning_ref::StableAddress;
-use std::ops::{Deref, DerefMut};
-
-/// `OwningHandle` is a complement to `OwningRef`. Where `OwningRef` allows
-/// consumers to pass around an owned object and a dependent reference,
-/// `OwningHandle` contains an owned object and a dependent _object_.
-///
-/// `OwningHandle` can encapsulate a `RefMut` along with its associated
-/// `RefCell`, or an `RwLockReadGuard` along with its associated `RwLock`.
-/// However, the API is completely generic and there are no restrictions on
-/// what types of owning and dependent objects may be used.
-///
-/// `OwningHandle` is created by passing an owner object (which dereferences
-/// to a stable address) along with a callback which receives a pointer to
-/// that stable location. The callback may then dereference the pointer and
-/// mint a dependent object, with the guarantee that the returned object will
-/// not outlive the referent of the pointer.
-///
-/// This does foist some unsafety onto the callback, which needs an `unsafe`
-/// block to dereference the pointer. It would be almost good enough for
-/// OwningHandle to pass a transmuted &'static reference to the callback
-/// since the lifetime is infinite as far as the minted handle is concerned.
-/// However, even an `Fn` callback can still allow the reference to escape
-/// via a `StaticMutex` or similar, which technically violates the safety
-/// contract. Some sort of language support in the lifetime system could
-/// make this API a bit nicer.
-pub struct OwningHandle<O, H>
-    where O: StableAddress,
-          H: Deref,
-{
-    handle: H,
-    _owner: O,
-}
-
-impl<O, H> Deref for OwningHandle<O, H>
-    where O: StableAddress,
-          H: Deref,
-{
-    type Target = H::Target;
-    fn deref(&self) -> &H::Target {
-        self.handle.deref()
-    }
-}
-
-unsafe impl<O, H> StableAddress for OwningHandle<O, H>
-    where O: StableAddress,
-          H: StableAddress,
-{}
-
-impl<O, H> DerefMut for OwningHandle<O, H>
-    where O: StableAddress,
-          H: DerefMut,
-{
-    fn deref_mut(&mut self) -> &mut H::Target {
-        self.handle.deref_mut()
-    }
-}
-
-impl<O, H> OwningHandle<O, H>
-    where O: StableAddress,
-          H: Deref,
-{
-    /// Create a new OwningHandle. The provided callback will be invoked with
-    /// a pointer to the object owned by `o`, and the returned value is stored
-    /// as the object to which this `OwningHandle` will forward `Deref` and
-    /// `DerefMut`.
-    pub fn new<F>(o: O, f: F) -> Self
-        where F: Fn(*const O::Target) -> H,
-    {
-        let h: H;
-        {
-            h = f(o.deref() as *const O::Target);
-        }
-
-        OwningHandle {
-          handle: h,
-          _owner: o,
-        }
-    }
-}
diff --git a/components/style/properties/properties.mako.rs b/components/style/properties/properties.mako.rs
index 7b81b9ae594..1ae30358efa 100644
--- a/components/style/properties/properties.mako.rs
+++ b/components/style/properties/properties.mako.rs
@@ -31,6 +31,7 @@ use parser::{Parse, ParserContext, ParserContextExtraData};
 use properties::animated_properties::TransitionProperty;
 #[cfg(feature = "servo")] use servo_config::prefs::PREFS;
 use servo_url::ServoUrl;
+use shared_lock::ReadGuards;
 use style_traits::ToCss;
 use stylesheets::Origin;
 #[cfg(feature = "servo")] use values::Either;
@@ -1860,6 +1861,7 @@ bitflags! {
 ///
 pub fn cascade(device: &Device,
                rule_node: &StrongRuleNode,
+               guards: &ReadGuards,
                parent_style: Option<<&ComputedValues>,
                layout_parent_style: Option<<&ComputedValues>,
                cascade_info: Option<<&mut CascadeInfo>,
@@ -1882,11 +1884,12 @@ pub fn cascade(device: &Device,
 
     // Hold locks until after the apply_declarations() call returns.
     // Use filter_map because the root node has no style source.
-    let lock_guards = rule_node.self_and_ancestors().filter_map(|node| {
-        node.style_source().map(|source| (source.read(), node.importance()))
+    let declaration_blocks = rule_node.self_and_ancestors().filter_map(|node| {
+        let guard = node.cascade_level().guard(guards);
+        node.style_source().map(|source| (source.read(guard), node.importance()))
     }).collect::<Vec<_>>();
     let iter_declarations = || {
-        lock_guards.iter().flat_map(|&(ref source, source_importance)| {
+        declaration_blocks.iter().flat_map(|&(ref source, source_importance)| {
             source.declarations().iter()
             // Yield declarations later in source order (with more precedence) first.
             .rev()
diff --git a/components/style/rule_tree/mod.rs b/components/style/rule_tree/mod.rs
index 9a725a19286..c1d4b27edf5 100644
--- a/components/style/rule_tree/mod.rs
+++ b/components/style/rule_tree/mod.rs
@@ -10,9 +10,9 @@
 use arc_ptr_eq;
 #[cfg(feature = "servo")]
 use heapsize::HeapSizeOf;
-use owning_handle::OwningHandle;
 use parking_lot::{RwLock, RwLockReadGuard};
 use properties::{Importance, PropertyDeclarationBlock};
+use shared_lock::{Locked, ReadGuards, SharedRwLockReadGuard};
 use std::io::{self, Write};
 use std::ptr;
 use std::sync::Arc;
@@ -52,35 +52,11 @@ pub struct RuleTree {
 #[derive(Debug, Clone)]
 pub enum StyleSource {
     /// A style rule stable pointer.
-    Style(Arc<RwLock<StyleRule>>),
+    Style(Arc<Locked<StyleRule>>),
     /// A declaration block stable pointer.
     Declarations(Arc<RwLock<PropertyDeclarationBlock>>),
 }
 
-type StyleSourceGuardHandle<'a> =
-    OwningHandle<
-        RwLockReadGuard<'a, StyleRule>,
-        RwLockReadGuard<'a, PropertyDeclarationBlock>>;
-
-/// A guard for a given style source.
-pub enum StyleSourceGuard<'a> {
-    /// A guard for a style rule.
-    Style(StyleSourceGuardHandle<'a>),
-    /// A guard for a declaration block.
-    Declarations(RwLockReadGuard<'a, PropertyDeclarationBlock>),
-}
-
-impl<'a> ::std::ops::Deref for StyleSourceGuard<'a> {
-    type Target = PropertyDeclarationBlock;
-
-    fn deref(&self) -> &Self::Target {
-        match *self {
-            StyleSourceGuard::Declarations(ref block) => &*block,
-            StyleSourceGuard::Style(ref handle) => &*handle,
-        }
-    }
-}
-
 impl StyleSource {
     #[inline]
     fn ptr_equals(&self, other: &Self) -> bool {
@@ -92,28 +68,27 @@ impl StyleSource {
         }
     }
 
-    fn dump<W: Write>(&self, writer: &mut W) {
+    fn dump<W: Write>(&self, guard: &SharedRwLockReadGuard, writer: &mut W) {
         use self::StyleSource::*;
 
         if let Style(ref rule) = *self {
-            let _ = write!(writer, "{:?}", rule.read().selectors);
+            let rule = rule.read_with(guard);
+            let _ = write!(writer, "{:?}", rule.selectors);
         }
 
-        let _ = write!(writer, "  -> {:?}", self.read().declarations());
+        let _ = write!(writer, "  -> {:?}", self.read(guard).declarations());
     }
 
     /// Read the style source guard, and obtain thus read access to the
     /// underlying property declaration block.
     #[inline]
-    pub fn read<'a>(&'a self) -> StyleSourceGuard<'a> {
-        use self::StyleSource::*;
-        match *self {
-            Style(ref rule) => {
-                let owning_ref = OwningHandle::new(rule.read(), |r| unsafe { &*r }.block.read());
-                StyleSourceGuard::Style(owning_ref)
-            }
-            Declarations(ref block) => StyleSourceGuard::Declarations(block.read()),
-        }
+    pub fn read<'a>(&'a self, guard: &'a SharedRwLockReadGuard)
+                    -> RwLockReadGuard<'a, PropertyDeclarationBlock> {
+        let block = match *self {
+            StyleSource::Style(ref rule) => &rule.read_with(guard).block,
+            StyleSource::Declarations(ref block) => block,
+        };
+        block.read()
     }
 }
 
@@ -137,15 +112,15 @@ impl RuleTree {
         self.root.clone()
     }
 
-    fn dump<W: Write>(&self, writer: &mut W) {
+    fn dump<W: Write>(&self, guards: &ReadGuards, writer: &mut W) {
         let _ = writeln!(writer, " + RuleTree");
-        self.root.get().dump(writer, 0);
+        self.root.get().dump(guards, writer, 0);
     }
 
     /// Dump the rule tree to stdout.
-    pub fn dump_stdout(&self) {
+    pub fn dump_stdout(&self, guards: &ReadGuards) {
         let mut stdout = io::stdout();
-        self.dump(&mut stdout);
+        self.dump(guards, &mut stdout);
     }
 
     /// Insert the given rules, that must be in proper order by specifity, and
@@ -307,6 +282,17 @@ pub enum CascadeLevel {
 }
 
 impl CascadeLevel {
+    /// Select a lock guard for this level
+    pub fn guard<'a>(&self, guards: &'a ReadGuards<'a>) -> &'a SharedRwLockReadGuard<'a> {
+        match *self {
+            CascadeLevel::UANormal |
+            CascadeLevel::UserNormal |
+            CascadeLevel::UserImportant |
+            CascadeLevel::UAImportant => guards.ua_or_user,
+            _ => guards.author,
+        }
+    }
+
     /// Returns whether this cascade level is unique per element, in which case
     /// we can replace the path in the cascade without fear.
     pub fn is_unique_per_element(&self) -> bool {
@@ -450,7 +436,7 @@ impl RuleNode {
         }
     }
 
-    fn dump<W: Write>(&self, writer: &mut W, indent: usize) {
+    fn dump<W: Write>(&self, guards: &ReadGuards, writer: &mut W, indent: usize) {
         const INDENT_INCREMENT: usize = 4;
 
         for _ in 0..indent {
@@ -467,7 +453,7 @@ impl RuleNode {
 
         match self.source {
             Some(ref source) => {
-                source.dump(writer);
+                source.dump(self.level.guard(guards), writer);
             }
             None => {
                 if indent != 0 {
@@ -479,7 +465,7 @@ impl RuleNode {
 
         let _ = write!(writer, "\n");
         for child in self.iter_children() {
-            child.get().dump(writer, indent + INDENT_INCREMENT);
+            child.get().dump(guards, writer, indent + INDENT_INCREMENT);
         }
     }
 
@@ -627,6 +613,11 @@ impl StrongRuleNode {
         self.get().source.as_ref()
     }
 
+    /// The cascade level for this node
+    pub fn cascade_level(&self) -> CascadeLevel {
+        self.get().level
+    }
+
     /// Get the importance that this rule node represents.
     pub fn importance(&self) -> Importance {
         self.get().level.importance()
diff --git a/components/style/servo/mod.rs b/components/style/servo/mod.rs
index ad741616eeb..ff6890658d3 100644
--- a/components/style/servo/mod.rs
+++ b/components/style/servo/mod.rs
@@ -9,3 +9,13 @@
 pub mod media_queries;
 pub mod restyle_damage;
 pub mod selector_parser;
+
+use shared_lock::SharedRwLock;
+
+lazy_static! {
+    /// Per-process shared lock for author-origin stylesheets
+    ///
+    /// FIXME: make it per-document or per-pipeline instead:
+    /// https://github.com/servo/servo/issues/16027
+    pub static ref AUTHOR_SHARED_LOCK: SharedRwLock = SharedRwLock::new();
+}
diff --git a/components/style/shared_lock.rs b/components/style/shared_lock.rs
index d4d66b8fc5d..c92ab9efccf 100644
--- a/components/style/shared_lock.rs
+++ b/components/style/shared_lock.rs
@@ -177,3 +177,23 @@ pub trait ToCssWithGuard {
         s
     }
 }
+
+/// Guards for a document
+#[derive(Clone)]
+pub struct ReadGuards<'a> {
+    /// For author-origin stylesheets
+    pub author: &'a SharedRwLockReadGuard<'a>,
+
+    /// For user-agent-origin and user-origin stylesheets
+    pub ua_or_user: &'a SharedRwLockReadGuard<'a>,
+}
+
+impl<'a> ReadGuards<'a> {
+    /// Same guard for all origins
+    pub fn same(guard: &'a SharedRwLockReadGuard<'a>) -> Self {
+        ReadGuards {
+            author: guard,
+            ua_or_user: guard,
+        }
+    }
+}
diff --git a/components/style/stylesheets.rs b/components/style/stylesheets.rs
index d132c64bbb9..96c553c4a49 100644
--- a/components/style/stylesheets.rs
+++ b/components/style/stylesheets.rs
@@ -215,7 +215,7 @@ pub enum CssRule {
 
     Namespace(Arc<Locked<NamespaceRule>>),
     Import(Arc<Locked<ImportRule>>),
-    Style(Arc<RwLock<StyleRule>>),
+    Style(Arc<Locked<StyleRule>>),
     Media(Arc<Locked<MediaRule>>),
     FontFace(Arc<Locked<FontFaceRule>>),
     Viewport(Arc<Locked<ViewportRule>>),
@@ -380,7 +380,7 @@ impl ToCssWithGuard for CssRule {
         match *self {
             CssRule::Namespace(ref lock) => lock.read_with(guard).to_css(guard, dest),
             CssRule::Import(ref lock) => lock.read_with(guard).to_css(guard, dest),
-            CssRule::Style(ref lock) => lock.read().to_css(guard, dest),
+            CssRule::Style(ref lock) => lock.read_with(guard).to_css(guard, dest),
             CssRule::FontFace(ref lock) => lock.read_with(guard).to_css(guard, dest),
             CssRule::Viewport(ref lock) => lock.read_with(guard).to_css(guard, dest),
             CssRule::Keyframes(ref lock) => lock.read_with(guard).to_css(guard, dest),
@@ -736,18 +736,6 @@ rule_filter! {
     effective_supports_rules(Supports => SupportsRule),
 }
 
-/// FIXME: Remove once StyleRule is actually in Locked<_>
-pub trait RwLockStyleRulePretendLockedStyleRule<T> {
-    /// Pretend we’re Locked<_>
-    fn read_with(&self, guard: &SharedRwLockReadGuard) -> ::parking_lot::RwLockReadGuard<T>;
-}
-
-impl RwLockStyleRulePretendLockedStyleRule<StyleRule> for RwLock<StyleRule> {
-    fn read_with(&self, _: &SharedRwLockReadGuard) -> ::parking_lot::RwLockReadGuard<StyleRule> {
-        self.read()
-    }
-}
-
 /// The stylesheet loader is the abstraction used to trigger network requests
 /// for `@import` rules.
 pub trait StylesheetLoader {
@@ -1030,7 +1018,7 @@ impl<'a, 'b> QualifiedRuleParser for NestedRuleParser<'a, 'b> {
 
     fn parse_block(&mut self, prelude: SelectorList<SelectorImpl>, input: &mut Parser)
                    -> Result<CssRule, ()> {
-        Ok(CssRule::Style(Arc::new(RwLock::new(StyleRule {
+        Ok(CssRule::Style(Arc::new(self.shared_lock.wrap(StyleRule {
             selectors: prelude,
             block: Arc::new(RwLock::new(parse_property_declaration_list(self.context, input)))
         }))))
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index a110e4f7abb..2166e81946a 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -28,7 +28,7 @@ use selectors::matching::{AFFECTED_BY_STYLE_ATTRIBUTE, AFFECTED_BY_PRESENTATIONA
 use selectors::matching::{ElementSelectorFlags, StyleRelations, matches_complex_selector};
 use selectors::parser::{Selector, SimpleSelector, LocalName as LocalNameSelector, ComplexSelector};
 use selectors::parser::SelectorMethods;
-use shared_lock::SharedRwLockReadGuard;
+use shared_lock::{Locked, SharedRwLockReadGuard, ReadGuards};
 use sink::Push;
 use smallvec::VecLike;
 use std::borrow::Borrow;
@@ -159,7 +159,7 @@ impl Stylist {
     /// device is dirty, which means we need to re-evaluate media queries.
     pub fn update(&mut self,
                   doc_stylesheets: &[Arc<Stylesheet>],
-                  doc_guard: &SharedRwLockReadGuard,
+                  guards: &ReadGuards,
                   ua_stylesheets: Option<&UserAgentStylesheets>,
                   stylesheets_changed: bool) -> bool {
         if !(self.is_device_dirty || stylesheets_changed) {
@@ -168,7 +168,7 @@ impl Stylist {
 
         let cascaded_rule = ViewportRule {
             declarations: viewport::Cascade::from_stylesheets(
-                doc_stylesheets, doc_guard, &self.device
+                doc_stylesheets, guards.author, &self.device
             ).finish(),
         };
 
@@ -196,18 +196,17 @@ impl Stylist {
         self.non_common_style_affecting_attributes_selectors.clear();
 
         if let Some(ua_stylesheets) = ua_stylesheets {
-            let ua_guard = ua_stylesheets.shared_lock.read();
             for stylesheet in &ua_stylesheets.user_or_user_agent_stylesheets {
-                self.add_stylesheet(&stylesheet, &ua_guard);
+                self.add_stylesheet(&stylesheet, guards.ua_or_user);
             }
 
             if self.quirks_mode {
-                self.add_stylesheet(&ua_stylesheets.quirks_mode_stylesheet, &ua_guard);
+                self.add_stylesheet(&ua_stylesheets.quirks_mode_stylesheet, guards.ua_or_user);
             }
         }
 
         for ref stylesheet in doc_stylesheets.iter() {
-            self.add_stylesheet(stylesheet, doc_guard);
+            self.add_stylesheet(stylesheet, guards.author);
         }
 
         debug!("Stylist stats:");
@@ -221,8 +220,9 @@ impl Stylist {
         SelectorImpl::each_precomputed_pseudo_element(|pseudo| {
             if let Some(map) = self.pseudos_map.remove(&pseudo) {
                 let declarations =
-                    map.user_agent.get_universal_rules(CascadeLevel::UANormal,
-                                                       CascadeLevel::UAImportant);
+                    map.user_agent.get_universal_rules(
+                        guards.ua_or_user, CascadeLevel::UANormal, CascadeLevel::UAImportant
+                    );
                 self.precomputed_pseudo_element_decls.insert(pseudo, declarations);
             }
         });
@@ -241,9 +241,9 @@ impl Stylist {
 
         stylesheet.effective_rules(&device, guard, |rule| {
             match *rule {
-                CssRule::Style(ref style_rule) => {
-                    let guard = style_rule.read();
-                    for selector in &guard.selectors.0 {
+                CssRule::Style(ref locked) => {
+                    let style_rule = locked.read_with(&guard);
+                    for selector in &style_rule.selectors.0 {
                         let map = if let Some(ref pseudo) = selector.pseudo_element {
                             self.pseudos_map
                                 .entry(pseudo.clone())
@@ -255,14 +255,14 @@ impl Stylist {
 
                         map.insert(Rule {
                             selector: selector.complex_selector.clone(),
-                            style_rule: style_rule.clone(),
+                            style_rule: locked.clone(),
                             specificity: selector.specificity,
                             source_order: self.rules_source_order,
                         });
                     }
                     self.rules_source_order += 1;
 
-                    for selector in &guard.selectors.0 {
+                    for selector in &style_rule.selectors.0 {
                         self.state_deps.note_selector(&selector.complex_selector);
                         if selector.affects_siblings() {
                             self.sibling_affecting_selectors.push(selector.clone());
@@ -300,6 +300,7 @@ impl Stylist {
     /// values. The flow constructor uses this flag when constructing anonymous
     /// flows.
     pub fn precomputed_values_for_pseudo(&self,
+                                         guards: &ReadGuards,
                                          pseudo: &PseudoElement,
                                          parent: Option<&Arc<ComputedValues>>,
                                          cascade_flags: CascadeFlags)
@@ -333,6 +334,7 @@ impl Stylist {
         let computed =
             properties::cascade(&self.device,
                                 &rule_node,
+                                guards,
                                 parent.map(|p| &**p),
                                 parent.map(|p| &**p),
                                 None,
@@ -344,6 +346,7 @@ impl Stylist {
     /// Returns the style for an anonymous box of the given type.
     #[cfg(feature = "servo")]
     pub fn style_for_anonymous_box(&self,
+                                   guards: &ReadGuards,
                                    pseudo: &PseudoElement,
                                    parent_style: &Arc<ComputedValues>)
                                    -> Arc<ComputedValues> {
@@ -368,7 +371,7 @@ impl Stylist {
         if inherit_all {
             cascade_flags.insert(INHERIT_ALL);
         }
-        self.precomputed_values_for_pseudo(&pseudo, Some(parent_style), cascade_flags)
+        self.precomputed_values_for_pseudo(guards, &pseudo, Some(parent_style), cascade_flags)
             .values.unwrap()
     }
 
@@ -380,6 +383,7 @@ impl Stylist {
     /// Check the documentation on lazy pseudo-elements in
     /// docs/components/style.md
     pub fn lazily_compute_pseudo_element_style<E>(&self,
+                                                  guards: &ReadGuards,
                                                   element: &E,
                                                   pseudo: &PseudoElement,
                                                   parent: &Arc<ComputedValues>)
@@ -401,6 +405,7 @@ impl Stylist {
                                           None,
                                           AnimationRules(None, None),
                                           Some(pseudo),
+                                          guards,
                                           &mut declarations,
                                           &mut flags);
 
@@ -415,6 +420,7 @@ impl Stylist {
         let computed =
             properties::cascade(&self.device,
                                 &rule_node,
+                                guards,
                                 Some(&**parent),
                                 Some(&**parent),
                                 None,
@@ -539,6 +545,7 @@ impl Stylist {
                                         style_attribute: Option<&Arc<RwLock<PropertyDeclarationBlock>>>,
                                         animation_rules: AnimationRules,
                                         pseudo_element: Option<&PseudoElement>,
+                                        guards: &ReadGuards,
                                         applicable_declarations: &mut V,
                                         flags: &mut ElementSelectorFlags) -> StyleRelations
         where E: TElement +
@@ -564,6 +571,7 @@ impl Stylist {
         // Step 1: Normal user-agent rules.
         map.user_agent.get_all_matching_rules(element,
                                               parent_bf,
+                                              guards.ua_or_user,
                                               applicable_declarations,
                                               &mut relations,
                                               flags,
@@ -588,6 +596,7 @@ impl Stylist {
             // Step 3: User and author normal rules.
             map.user.get_all_matching_rules(element,
                                             parent_bf,
+                                            guards.ua_or_user,
                                             applicable_declarations,
                                             &mut relations,
                                             flags,
@@ -595,6 +604,7 @@ impl Stylist {
             debug!("user normal: {:?}", relations);
             map.author.get_all_matching_rules(element,
                                               parent_bf,
+                                              guards.author,
                                               applicable_declarations,
                                               &mut relations,
                                               flags,
@@ -629,6 +639,7 @@ impl Stylist {
             // Step 6: Author-supplied `!important` rules.
             map.author.get_all_matching_rules(element,
                                               parent_bf,
+                                              guards.author,
                                               applicable_declarations,
                                               &mut relations,
                                               flags,
@@ -652,6 +663,7 @@ impl Stylist {
             // Step 8: User `!important` rules.
             map.user.get_all_matching_rules(element,
                                             parent_bf,
+                                            guards.ua_or_user,
                                             applicable_declarations,
                                             &mut relations,
                                             flags,
@@ -665,6 +677,7 @@ impl Stylist {
         // Step 9: UA `!important` rules.
         map.user_agent.get_all_matching_rules(element,
                                               parent_bf,
+                                              guards.ua_or_user,
                                               applicable_declarations,
                                               &mut relations,
                                               flags,
@@ -903,6 +916,7 @@ impl SelectorMap {
     pub fn get_all_matching_rules<E, V>(&self,
                                         element: &E,
                                         parent_bf: Option<&BloomFilter>,
+                                        guard: &SharedRwLockReadGuard,
                                         matching_rules_list: &mut V,
                                         relations: &mut StyleRelations,
                                         flags: &mut ElementSelectorFlags,
@@ -921,6 +935,7 @@ impl SelectorMap {
                                                       parent_bf,
                                                       &self.id_hash,
                                                       &id,
+                                                      guard,
                                                       matching_rules_list,
                                                       relations,
                                                       flags,
@@ -932,6 +947,7 @@ impl SelectorMap {
                                                       parent_bf,
                                                       &self.class_hash,
                                                       class,
+                                                      guard,
                                                       matching_rules_list,
                                                       relations,
                                                       flags,
@@ -947,6 +963,7 @@ impl SelectorMap {
                                                   parent_bf,
                                                   local_name_hash,
                                                   element.get_local_name(),
+                                                  guard,
                                                   matching_rules_list,
                                                   relations,
                                                   flags,
@@ -955,6 +972,7 @@ impl SelectorMap {
         SelectorMap::get_matching_rules(element,
                                         parent_bf,
                                         &self.other_rules,
+                                        guard,
                                         matching_rules_list,
                                         relations,
                                         flags,
@@ -968,6 +986,7 @@ impl SelectorMap {
     /// Append to `rule_list` all universal Rules (rules with selector `*|*`) in
     /// `self` sorted by specificity and source order.
     pub fn get_universal_rules(&self,
+                               guard: &SharedRwLockReadGuard,
                                cascade_level: CascadeLevel,
                                important_cascade_level: CascadeLevel)
                                -> Vec<ApplicableDeclarationBlock> {
@@ -985,8 +1004,8 @@ impl SelectorMap {
         for rule in self.other_rules.iter() {
             if rule.selector.compound_selector.is_empty() &&
                rule.selector.next.is_none() {
-                let guard = rule.style_rule.read();
-                let block = guard.block.read();
+                let style_rule = rule.style_rule.read_with(guard);
+                let block = style_rule.block.read();
                 if block.any_normal() {
                     matching_rules_list.push(
                         rule.to_applicable_declaration_block(cascade_level));
@@ -1014,6 +1033,7 @@ impl SelectorMap {
         parent_bf: Option<&BloomFilter>,
         hash: &FnvHashMap<Str, Vec<Rule>>,
         key: &BorrowedStr,
+        guard: &SharedRwLockReadGuard,
         matching_rules: &mut Vector,
         relations: &mut StyleRelations,
         flags: &mut ElementSelectorFlags,
@@ -1027,6 +1047,7 @@ impl SelectorMap {
             SelectorMap::get_matching_rules(element,
                                             parent_bf,
                                             rules,
+                                            guard,
                                             matching_rules,
                                             relations,
                                             flags,
@@ -1038,6 +1059,7 @@ impl SelectorMap {
     fn get_matching_rules<E, V>(element: &E,
                                 parent_bf: Option<&BloomFilter>,
                                 rules: &[Rule],
+                                guard: &SharedRwLockReadGuard,
                                 matching_rules: &mut V,
                                 relations: &mut StyleRelations,
                                 flags: &mut ElementSelectorFlags,
@@ -1046,8 +1068,8 @@ impl SelectorMap {
               V: VecLike<ApplicableDeclarationBlock>
     {
         for rule in rules.iter() {
-            let guard = rule.style_rule.read();
-            let block = guard.block.read();
+            let style_rule = rule.style_rule.read_with(guard);
+            let block = style_rule.block.read();
             let any_declaration_for_importance = if cascade_level.is_important() {
                 block.any_important()
             } else {
@@ -1145,7 +1167,7 @@ pub struct Rule {
     pub selector: Arc<ComplexSelector<SelectorImpl>>,
     /// The actual style rule.
     #[cfg_attr(feature = "servo", ignore_heap_size_of = "Arc")]
-    pub style_rule: Arc<RwLock<StyleRule>>,
+    pub style_rule: Arc<Locked<StyleRule>>,
     /// The source order this style rule appears in.
     pub source_order: usize,
     /// The specificity of the rule this selector represents.
diff --git a/components/style/traversal.rs b/components/style/traversal.rs
index 5c413b9c6bb..1b7c8042bae 100644
--- a/components/style/traversal.rs
+++ b/components/style/traversal.rs
@@ -312,7 +312,8 @@ pub trait DomTraversal<E: TElement> : Sync {
 }
 
 /// Helper for the function below.
-fn resolve_style_internal<E, F>(context: &mut StyleContext<E>, element: E, ensure_data: &F)
+fn resolve_style_internal<E, F>(context: &mut StyleContext<E>,
+                                element: E, ensure_data: &F)
                                 -> Option<E>
     where E: TElement,
           F: Fn(E),
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index 24380439062..bbe8bc6907d 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -23,7 +23,6 @@ use style::context::{ThreadLocalStyleContext, ThreadLocalStyleContextCreationInf
 use style::data::{ElementData, ElementStyles, RestyleData};
 use style::dom::{ShowSubtreeData, TElement, TNode};
 use style::error_reporting::StdoutErrorReporter;
-use style::gecko::arc_types::HackHackHack;
 use style::gecko::data::{PerDocumentStyleData, PerDocumentStyleDataImpl};
 use style::gecko::restyle_damage::GeckoRestyleDamage;
 use style::gecko::selector_parser::{SelectorImpl, PseudoElement};
@@ -77,12 +76,11 @@ use style::properties::parse_one_declaration;
 use style::restyle_hints::{self, RestyleHint};
 use style::selector_parser::PseudoElementCascadeType;
 use style::sequential;
-use style::shared_lock::{SharedRwLock, ToCssWithGuard, Locked};
+use style::shared_lock::{SharedRwLock, SharedRwLockReadGuard, ReadGuards, ToCssWithGuard, Locked};
 use style::string_cache::Atom;
 use style::stylesheets::{CssRule, CssRules, ImportRule, MediaRule, NamespaceRule};
 use style::stylesheets::{Origin, Stylesheet, StyleRule};
 use style::stylesheets::StylesheetLoader as StyleStylesheetLoader;
-use style::stylesheets::RwLockStyleRulePretendLockedStyleRule;
 use style::supports::parse_condition_or_declaration;
 use style::thread_state;
 use style::timer::Timer;
@@ -167,12 +165,14 @@ pub extern "C" fn Servo_Shutdown() {
     gecko_properties::shutdown();
 }
 
-fn create_shared_context(per_doc_data: &PerDocumentStyleDataImpl) -> SharedStyleContext {
+fn create_shared_context<'a>(guard: &'a SharedRwLockReadGuard,
+                             per_doc_data: &PerDocumentStyleDataImpl) -> SharedStyleContext<'a> {
     let local_context_data =
         ThreadLocalStyleContextCreationInfo::new(per_doc_data.new_animations_sender.clone());
 
     SharedStyleContext {
         stylist: per_doc_data.stylist.clone(),
+        guards: ReadGuards::same(guard),
         running_animations: per_doc_data.running_animations.clone(),
         expired_animations: per_doc_data.expired_animations.clone(),
         // FIXME(emilio): Stop boxing here.
@@ -205,8 +205,9 @@ fn traverse_subtree(element: GeckoElement, raw_data: RawServoStyleSetBorrowed,
     debug!("Traversing subtree:");
     debug!("{:?}", ShowSubtreeData(element.as_node()));
 
-    let shared_style_context = create_shared_context(&per_doc_data);
     let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let shared_style_context = create_shared_context(&guard, &per_doc_data);
 
     let traversal_driver = if global_style_data.style_thread_pool.is_none() {
         TraversalDriver::Sequential
@@ -625,22 +626,28 @@ impl_basic_rule_funcs! { (Namespace, NamespaceRule, RawServoNamespaceRule),
 
 #[no_mangle]
 pub extern "C" fn Servo_StyleRule_GetStyle(rule: RawServoStyleRuleBorrowed) -> RawServoDeclarationBlockStrong {
-    let rule = RwLock::<StyleRule>::as_arc(&rule);
-    rule.read().block.clone().into_strong()
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let rule = Locked::<StyleRule>::as_arc(&rule);
+    rule.read_with(&guard).block.clone().into_strong()
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_StyleRule_SetStyle(rule: RawServoStyleRuleBorrowed,
                                            declarations: RawServoDeclarationBlockBorrowed) {
-    let rule = RwLock::<StyleRule>::as_arc(&rule);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    let rule = Locked::<StyleRule>::as_arc(&rule);
     let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
-    rule.write().block = declarations.clone();
+    rule.write_with(&mut guard).block = declarations.clone();
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_StyleRule_GetSelectorText(rule: RawServoStyleRuleBorrowed, result: *mut nsAString) {
-    let rule = RwLock::<StyleRule>::as_arc(&rule);
-    rule.read().selectors.to_css(unsafe { result.as_mut().unwrap() }).unwrap();
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let rule = Locked::<StyleRule>::as_arc(&rule);
+    rule.read_with(&guard).selectors.to_css(unsafe { result.as_mut().unwrap() }).unwrap();
 }
 
 #[no_mangle]
@@ -681,6 +688,9 @@ pub extern "C" fn Servo_ComputedValues_GetForAnonymousBox(parent_style_or_null:
                                                           skip_display_fixup: bool,
                                                           raw_data: RawServoStyleSetBorrowed)
      -> ServoComputedValuesStrong {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let guards = ReadGuards::same(&guard);
     let data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
     let atom = Atom::from(pseudo_tag);
     let pseudo = PseudoElement::from_atom_unchecked(atom, /* anon_box = */ true);
@@ -691,7 +701,7 @@ pub extern "C" fn Servo_ComputedValues_GetForAnonymousBox(parent_style_or_null:
     if skip_display_fixup {
         cascade_flags.insert(SKIP_ROOT_AND_ITEM_BASED_DISPLAY_FIXUP);
     }
-    data.stylist.precomputed_values_for_pseudo(&pseudo, maybe_parent,
+    data.stylist.precomputed_values_for_pseudo(&guards, &pseudo, maybe_parent,
                                                cascade_flags)
         .values.unwrap()
         .into_strong()
@@ -717,14 +727,16 @@ pub extern "C" fn Servo_ResolvePseudoStyle(element: RawGeckoElementBorrowed,
         };
     }
 
-    match get_pseudo_style(element, pseudo_tag, data.styles(), doc_data) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    match get_pseudo_style(&guard, element, pseudo_tag, data.styles(), doc_data) {
         Some(values) => values.into_strong(),
         None if !is_probe => data.styles().primary.values().clone().into_strong(),
         None => Strong::null(),
     }
 }
 
-fn get_pseudo_style(element: GeckoElement, pseudo_tag: *mut nsIAtom,
+fn get_pseudo_style(guard: &SharedRwLockReadGuard, element: GeckoElement, pseudo_tag: *mut nsIAtom,
                     styles: &ElementStyles, doc_data: &PerDocumentStyleData)
                     -> Option<Arc<ComputedValues>>
 {
@@ -735,7 +747,9 @@ fn get_pseudo_style(element: GeckoElement, pseudo_tag: *mut nsIAtom,
         PseudoElementCascadeType::Lazy => {
             let d = doc_data.borrow_mut();
             let base = styles.primary.values();
-            d.stylist.lazily_compute_pseudo_element_style(&element,
+            let guards = ReadGuards::same(guard);
+            d.stylist.lazily_compute_pseudo_element_style(&guards,
+                                                          &element,
                                                           &pseudo,
                                                           base)
                      .map(|s| s.values().clone())
@@ -1463,11 +1477,13 @@ pub extern "C" fn Servo_ResolveStyleLazily(element: RawGeckoElementBorrowed,
                                            raw_data: RawServoStyleSetBorrowed)
      -> ServoComputedValuesStrong
 {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
     let element = GeckoElement(element);
     let doc_data = PerDocumentStyleData::from_ffi(raw_data);
     let finish = |styles: &ElementStyles| -> Arc<ComputedValues> {
         let maybe_pseudo = if !pseudo_tag.is_null() {
-            get_pseudo_style(element, pseudo_tag, styles, doc_data)
+            get_pseudo_style(&guard, element, pseudo_tag, styles, doc_data)
         } else {
             None
         };
@@ -1483,7 +1499,7 @@ pub extern "C" fn Servo_ResolveStyleLazily(element: RawGeckoElementBorrowed,
     }
 
     // We don't have the style ready. Go ahead and compute it as necessary.
-    let shared = create_shared_context(&mut doc_data.borrow_mut());
+    let shared = create_shared_context(&guard, &mut doc_data.borrow_mut());
     let mut tlc = ThreadLocalStyleContext::new(&shared);
     let mut context = StyleContext {
         shared: &shared,
diff --git a/tests/unit/style/Cargo.toml b/tests/unit/style/Cargo.toml
index 98838676937..7939e617342 100644
--- a/tests/unit/style/Cargo.toml
+++ b/tests/unit/style/Cargo.toml
@@ -17,7 +17,6 @@ app_units = "0.4"
 cssparser = "0.12"
 euclid = "0.11"
 html5ever-atoms = "0.2"
-owning_ref = "0.2.2"
 parking_lot = "0.3"
 rayon = "0.6"
 rustc-serialize = "0.3"
diff --git a/tests/unit/style/lib.rs b/tests/unit/style/lib.rs
index 9d7cdcae651..887de470ffa 100644
--- a/tests/unit/style/lib.rs
+++ b/tests/unit/style/lib.rs
@@ -9,7 +9,6 @@ extern crate app_units;
 extern crate cssparser;
 extern crate euclid;
 #[macro_use] extern crate html5ever_atoms;
-extern crate owning_ref;
 extern crate parking_lot;
 extern crate rayon;
 extern crate rustc_serialize;
@@ -26,7 +25,6 @@ mod attr;
 mod keyframes;
 mod logical_geometry;
 mod media_queries;
-mod owning_handle;
 mod parsing;
 mod properties;
 mod rule_tree;
diff --git a/tests/unit/style/owning_handle.rs b/tests/unit/style/owning_handle.rs
deleted file mode 100644
index cf792ef9605..00000000000
--- a/tests/unit/style/owning_handle.rs
+++ /dev/null
@@ -1,34 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-use owning_ref::RcRef;
-use std::cell::RefCell;
-use std::rc::Rc;
-use std::sync::{Arc, RwLock};
-use style::owning_handle::OwningHandle;
-
-#[test]
-fn owning_handle() {
-    use std::cell::RefCell;
-    let cell = Rc::new(RefCell::new(2));
-    let cell_ref = RcRef::new(cell);
-    let mut handle = OwningHandle::new(cell_ref, |x| unsafe { x.as_ref() }.unwrap().borrow_mut());
-    assert_eq!(*handle, 2);
-    *handle = 3;
-    assert_eq!(*handle, 3);
-}
-
-#[test]
-fn nested() {
-    let result = {
-        let complex = Rc::new(RefCell::new(Arc::new(RwLock::new("someString"))));
-        let curr = RcRef::new(complex);
-        let curr = OwningHandle::new(curr, |x| unsafe { x.as_ref() }.unwrap().borrow_mut());
-        let mut curr = OwningHandle::new(curr, |x| unsafe { x.as_ref() }.unwrap().try_write().unwrap());
-        assert_eq!(*curr, "someString");
-        *curr = "someOtherString";
-        curr
-    };
-    assert_eq!(*result, "someOtherString");
-}
diff --git a/tests/unit/style/stylesheets.rs b/tests/unit/style/stylesheets.rs
index 99ec3676236..2bcb9b58a77 100644
--- a/tests/unit/style/stylesheets.rs
+++ b/tests/unit/style/stylesheets.rs
@@ -81,7 +81,7 @@ fn test_parse_stylesheet() {
                 prefix: None,
                 url: NsAtom::from("http://www.w3.org/1999/xhtml")
             }))),
-            CssRule::Style(Arc::new(RwLock::new(StyleRule {
+            CssRule::Style(Arc::new(stylesheet.shared_lock.wrap(StyleRule {
                 selectors: SelectorList(vec![
                     Selector {
                         complex_selector: Arc::new(ComplexSelector {
@@ -117,7 +117,7 @@ fn test_parse_stylesheet() {
                      Importance::Important),
                 ]))),
             }))),
-            CssRule::Style(Arc::new(RwLock::new(StyleRule {
+            CssRule::Style(Arc::new(stylesheet.shared_lock.wrap(StyleRule {
                 selectors: SelectorList(vec![
                     Selector {
                         complex_selector: Arc::new(ComplexSelector {
@@ -159,7 +159,7 @@ fn test_parse_stylesheet() {
                      Importance::Normal),
                 ]))),
             }))),
-            CssRule::Style(Arc::new(RwLock::new(StyleRule {
+            CssRule::Style(Arc::new(stylesheet.shared_lock.wrap(StyleRule {
                 selectors: SelectorList(vec![
                     Selector {
                         complex_selector: Arc::new(ComplexSelector {
diff --git a/tests/unit/style/stylist.rs b/tests/unit/style/stylist.rs
index ab04f2e5dd5..34a7feff965 100644
--- a/tests/unit/style/stylist.rs
+++ b/tests/unit/style/stylist.rs
@@ -11,17 +11,19 @@ use style::properties::{PropertyDeclarationBlock, PropertyDeclaration};
 use style::properties::{longhands, Importance};
 use style::rule_tree::CascadeLevel;
 use style::selector_parser::SelectorParser;
+use style::shared_lock::SharedRwLock;
 use style::stylesheets::StyleRule;
 use style::stylist::{Rule, SelectorMap};
 use style::thread_state;
 
 /// Helper method to get some Rules from selector strings.
 /// Each sublist of the result contains the Rules for one StyleRule.
-fn get_mock_rules(css_selectors: &[&str]) -> Vec<Vec<Rule>> {
-    css_selectors.iter().enumerate().map(|(i, selectors)| {
+fn get_mock_rules(css_selectors: &[&str]) -> (Vec<Vec<Rule>>, SharedRwLock) {
+    let shared_lock = SharedRwLock::new();
+    (css_selectors.iter().enumerate().map(|(i, selectors)| {
         let selectors = SelectorParser::parse_author_origin_no_namespace(selectors).unwrap();
 
-        let rule = Arc::new(RwLock::new(StyleRule {
+        let locked = Arc::new(shared_lock.wrap(StyleRule {
             selectors: selectors,
             block: Arc::new(RwLock::new(PropertyDeclarationBlock::with_one(
                 PropertyDeclaration::Display(
@@ -30,21 +32,22 @@ fn get_mock_rules(css_selectors: &[&str]) -> Vec<Vec<Rule>> {
             ))),
         }));
 
-        let guard = rule.read();
-        guard.selectors.0.iter().map(|s| {
+        let guard = shared_lock.read();
+        let rule = locked.read_with(&guard);
+        rule.selectors.0.iter().map(|s| {
             Rule {
                 selector: s.complex_selector.clone(),
-                style_rule: rule.clone(),
+                style_rule: locked.clone(),
                 specificity: s.specificity,
                 source_order: i,
             }
         }).collect()
-    }).collect()
+    }).collect(), shared_lock)
 }
 
-fn get_mock_map(selectors: &[&str]) -> SelectorMap {
+fn get_mock_map(selectors: &[&str]) -> (SelectorMap, SharedRwLock) {
     let mut map = SelectorMap::new();
-    let selector_rules = get_mock_rules(selectors);
+    let (selector_rules, shared_lock) = get_mock_rules(selectors);
 
     for rules in selector_rules.into_iter() {
         for rule in rules.into_iter() {
@@ -52,12 +55,12 @@ fn get_mock_map(selectors: &[&str]) -> SelectorMap {
         }
     }
 
-    map
+    (map, shared_lock)
 }
 
 #[test]
 fn test_rule_ordering_same_specificity() {
-    let rules_list = get_mock_rules(&["a.intro", "img.sidebar"]);
+    let (rules_list, _) = get_mock_rules(&["a.intro", "img.sidebar"]);
     let a = &rules_list[0][0];
     let b = &rules_list[1][0];
     assert!((a.specificity, a.source_order) < ((b.specificity, b.source_order)),
@@ -67,21 +70,21 @@ fn test_rule_ordering_same_specificity() {
 
 #[test]
 fn test_get_id_name() {
-    let rules_list = get_mock_rules(&[".intro", "#top"]);
+    let (rules_list, _) = get_mock_rules(&[".intro", "#top"]);
     assert_eq!(SelectorMap::get_id_name(&rules_list[0][0]), None);
     assert_eq!(SelectorMap::get_id_name(&rules_list[1][0]), Some(Atom::from("top")));
 }
 
 #[test]
 fn test_get_class_name() {
-    let rules_list = get_mock_rules(&[".intro.foo", "#top"]);
+    let (rules_list, _) = get_mock_rules(&[".intro.foo", "#top"]);
     assert_eq!(SelectorMap::get_class_name(&rules_list[0][0]), Some(Atom::from("intro")));
     assert_eq!(SelectorMap::get_class_name(&rules_list[1][0]), None);
 }
 
 #[test]
 fn test_get_local_name() {
-    let rules_list = get_mock_rules(&["img.foo", "#top", "IMG", "ImG"]);
+    let (rules_list, _) = get_mock_rules(&["img.foo", "#top", "IMG", "ImG"]);
     let check = |i: usize, names: Option<(&str, &str)>| {
         assert!(SelectorMap::get_local_name(&rules_list[i][0])
                 == names.map(|(name, lower_name)| LocalNameSelector {
@@ -96,7 +99,7 @@ fn test_get_local_name() {
 
 #[test]
 fn test_insert() {
-    let rules_list = get_mock_rules(&[".intro.foo", "#top"]);
+    let (rules_list, _) = get_mock_rules(&[".intro.foo", "#top"]);
     let mut selector_map = SelectorMap::new();
     selector_map.insert(rules_list[1][0].clone());
     assert_eq!(1, selector_map.id_hash.get(&Atom::from("top")).unwrap()[0].source_order);
@@ -108,10 +111,11 @@ fn test_insert() {
 #[test]
 fn test_get_universal_rules() {
     thread_state::initialize(thread_state::LAYOUT);
-    let map = get_mock_map(&["*|*", "#foo > *|*", ".klass", "#id"]);
+    let (map, shared_lock) = get_mock_map(&["*|*", "#foo > *|*", ".klass", "#id"]);
 
-    let decls = map.get_universal_rules(CascadeLevel::UserNormal,
-                                        CascadeLevel::UserImportant);
+    let guard = shared_lock.read();
+    let decls = map.get_universal_rules(
+        &guard, CascadeLevel::UserNormal, CascadeLevel::UserImportant);
 
     assert_eq!(decls.len(), 1);
 }

From 1bacd0eb1582f609ad9a9c9a8a33a737bf4bc6f3 Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Sat, 18 Mar 2017 02:10:00 +0100
Subject: [PATCH 12/17] Move all PropertyDeclarationBlock from RwLock<_> to
 Locked<_>

---
 Cargo.lock                                   |   3 +-
 components/script/dom/bindings/trace.rs      |   2 +-
 components/script/dom/csskeyframerule.rs     |   5 +-
 components/script/dom/cssstyledeclaration.rs |  32 ++-
 components/script/dom/element.rs             |  37 +++-
 components/script/layout_wrapper.rs          |   5 +-
 components/style/Cargo.toml                  |   3 +-
 components/style/animation.rs                |   2 +-
 components/style/attr.rs                     |   4 +-
 components/style/dom.rs                      |  12 +-
 components/style/gecko/arc_types.rs          |   2 +-
 components/style/gecko/global_style_data.rs  |  50 +++++
 components/style/gecko/mod.rs                |   1 +
 components/style/gecko/wrapper.rs            |  14 +-
 components/style/keyframes.rs                |  37 ++--
 components/style/lib.rs                      |   1 +
 components/style/matching.rs                 |   6 +-
 components/style/rule_tree/mod.rs            |  17 +-
 components/style/stylesheets.rs              |  11 +-
 components/style/stylist.rs                  |  13 +-
 ports/geckolib/Cargo.toml                    |   2 -
 ports/geckolib/glue.rs                       | 219 ++++++++++---------
 ports/geckolib/lib.rs                        |   2 -
 ports/geckolib/stylesheet_loader.rs          |   2 +-
 tests/unit/style/keyframes.rs                |  17 +-
 tests/unit/style/rule_tree/bench.rs          |  17 +-
 tests/unit/style/stylesheets.rs              |  10 +-
 tests/unit/style/stylist.rs                  |   3 +-
 28 files changed, 321 insertions(+), 208 deletions(-)
 create mode 100644 components/style/gecko/global_style_data.rs

diff --git a/Cargo.lock b/Cargo.lock
index 076924c397c..72065507be0 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -928,9 +928,7 @@ dependencies = [
  "lazy_static 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.21 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
- "num_cpus 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "rayon 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "selectors 0.18.0",
  "servo_url 0.0.1",
  "style 0.0.1",
@@ -2756,6 +2754,7 @@ dependencies = [
  "nsstring_vendor 0.1.0",
  "num-integer 0.1.33 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num_cpus 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "ordered-float 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "pdqsort 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index 7cad9f98523..ee90766b1e2 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -562,7 +562,7 @@ unsafe impl JSTraceable for StyleLocked<ViewportRule> {
     }
 }
 
-unsafe impl JSTraceable for RwLock<PropertyDeclarationBlock> {
+unsafe impl JSTraceable for StyleLocked<PropertyDeclarationBlock> {
     unsafe fn trace(&self, _trc: *mut JSTracer) {
         // Do nothing.
     }
diff --git a/components/script/dom/csskeyframerule.rs b/components/script/dom/csskeyframerule.rs
index 617546d6a76..d36e8988e04 100644
--- a/components/script/dom/csskeyframerule.rs
+++ b/components/script/dom/csskeyframerule.rs
@@ -14,8 +14,7 @@ use dom::window::Window;
 use dom_struct::dom_struct;
 use std::sync::Arc;
 use style::keyframes::Keyframe;
-use style::shared_lock::Locked;
-use style_traits::ToCss;
+use style::shared_lock::{Locked, ToCssWithGuard};
 
 #[dom_struct]
 pub struct CSSKeyframeRule {
@@ -70,6 +69,6 @@ impl SpecificCSSRule for CSSKeyframeRule {
 
     fn get_css(&self) -> DOMString {
         let guard = self.cssrule.shared_lock().read();
-        self.keyframerule.read_with(&guard).to_css_string().into()
+        self.keyframerule.read_with(&guard).to_css_string(&guard).into()
     }
 }
diff --git a/components/script/dom/cssstyledeclaration.rs b/components/script/dom/cssstyledeclaration.rs
index 8af3b3975d2..d5d248f7880 100644
--- a/components/script/dom/cssstyledeclaration.rs
+++ b/components/script/dom/cssstyledeclaration.rs
@@ -11,10 +11,9 @@ use dom::bindings::reflector::{DomObject, Reflector, reflect_dom_object};
 use dom::bindings::str::DOMString;
 use dom::cssrule::CSSRule;
 use dom::element::Element;
-use dom::node::{Node, window_from_node};
+use dom::node::{Node, window_from_node, document_from_node};
 use dom::window::Window;
 use dom_struct::dom_struct;
-use parking_lot::RwLock;
 use servo_url::ServoUrl;
 use std::ascii::AsciiExt;
 use std::sync::Arc;
@@ -23,6 +22,7 @@ use style::parser::ParserContextExtraData;
 use style::properties::{Importance, PropertyDeclarationBlock, PropertyId, LonghandId, ShorthandId};
 use style::properties::{parse_one_declaration, parse_style_attribute};
 use style::selector_parser::PseudoElement;
+use style::shared_lock::Locked;
 use style_traits::ToCss;
 
 // http://dev.w3.org/csswg/cssom/#the-cssstyledeclaration-interface
@@ -40,7 +40,7 @@ pub enum CSSStyleOwner {
     Element(JS<Element>),
     CSSRule(JS<CSSRule>,
             #[ignore_heap_size_of = "Arc"]
-            Arc<RwLock<PropertyDeclarationBlock>>),
+            Arc<Locked<PropertyDeclarationBlock>>),
 }
 
 impl CSSStyleOwner {
@@ -55,10 +55,13 @@ impl CSSStyleOwner {
         let mut changed = true;
         match *self {
             CSSStyleOwner::Element(ref el) => {
+                let document = document_from_node(&**el);
+                let shared_lock = document.style_shared_lock();
                 let mut attr = el.style_attribute().borrow_mut().take();
                 let result = if attr.is_some() {
                     let lock = attr.as_ref().unwrap();
-                    let mut pdb = lock.write();
+                    let mut guard = shared_lock.write();
+                    let mut pdb = lock.write_with(&mut guard);
                     let result = f(&mut pdb, &mut changed);
                     result
                 } else {
@@ -69,7 +72,7 @@ impl CSSStyleOwner {
                     // exact conditions under it changes.
                     changed = !pdb.declarations().is_empty();
                     if changed {
-                        attr = Some(Arc::new(RwLock::new(pdb)));
+                        attr = Some(Arc::new(shared_lock.wrap(pdb)));
                     }
 
                     result
@@ -83,7 +86,8 @@ impl CSSStyleOwner {
                     //
                     // [1]: https://github.com/whatwg/html/issues/2306
                     if let Some(pdb) = attr {
-                        let serialization = pdb.read().to_css_string();
+                        let guard = shared_lock.read();
+                        let serialization = pdb.read_with(&guard).to_css_string();
                         el.set_attribute(&local_name!("style"),
                                          AttrValue::Declaration(serialization,
                                                                 pdb));
@@ -96,7 +100,10 @@ impl CSSStyleOwner {
                 result
             }
             CSSStyleOwner::CSSRule(ref rule, ref pdb) => {
-                let result = f(&mut *pdb.write(), &mut changed);
+                let result = {
+                    let mut guard = rule.shared_lock().write();
+                    f(&mut *pdb.write_with(&mut guard), &mut changed)
+                };
                 if changed {
                     rule.global().as_window().Document().invalidate_stylesheets();
                 }
@@ -111,15 +118,20 @@ impl CSSStyleOwner {
         match *self {
             CSSStyleOwner::Element(ref el) => {
                 match *el.style_attribute().borrow() {
-                    Some(ref pdb) => f(&pdb.read()),
+                    Some(ref pdb) => {
+                        let document = document_from_node(&**el);
+                        let guard = document.style_shared_lock().read();
+                        f(pdb.read_with(&guard))
+                    }
                     None => {
                         let pdb = PropertyDeclarationBlock::new();
                         f(&pdb)
                     }
                 }
             }
-            CSSStyleOwner::CSSRule(_, ref pdb) => {
-                f(&pdb.read())
+            CSSStyleOwner::CSSRule(ref rule, ref pdb) => {
+                let guard = rule.shared_lock().read();
+                f(pdb.read_with(&guard))
             }
         }
     }
diff --git a/components/script/dom/element.rs b/components/script/dom/element.rs
index 8e13716fa9d..3a73bbce97e 100644
--- a/components/script/dom/element.rs
+++ b/components/script/dom/element.rs
@@ -82,7 +82,6 @@ use html5ever::serialize::TraversalScope::{ChildrenOnly, IncludeNode};
 use html5ever_atoms::{Prefix, LocalName, Namespace, QualName};
 use js::jsapi::{HandleValue, JSAutoCompartment};
 use net_traits::request::CorsSettings;
-use parking_lot::RwLock;
 use ref_filter_map::ref_filter_map;
 use script_layout_interface::message::ReflowQueryType;
 use script_thread::Runnable;
@@ -108,6 +107,7 @@ use style::properties::longhands::{self, background_image, border_spacing, font_
 use style::restyle_hints::RESTYLE_SELF;
 use style::rule_tree::CascadeLevel;
 use style::selector_parser::{NonTSPseudoClass, RestyleDamage, SelectorImpl, SelectorParser};
+use style::shared_lock::{SharedRwLock, Locked};
 use style::sink::Push;
 use style::stylist::ApplicableDeclarationBlock;
 use style::thread_state;
@@ -129,7 +129,7 @@ pub struct Element {
     attrs: DOMRefCell<Vec<JS<Attr>>>,
     id_attribute: DOMRefCell<Option<Atom>>,
     #[ignore_heap_size_of = "Arc"]
-    style_attribute: DOMRefCell<Option<Arc<RwLock<PropertyDeclarationBlock>>>>,
+    style_attribute: DOMRefCell<Option<Arc<Locked<PropertyDeclarationBlock>>>>,
     attr_list: MutNullableJS<NamedNodeMap>,
     class_list: MutNullableJS<DOMTokenList>,
     state: Cell<ElementState>,
@@ -352,7 +352,7 @@ pub trait LayoutElementHelpers {
     #[allow(unsafe_code)]
     unsafe fn html_element_in_html_document_for_layout(&self) -> bool;
     fn id_attribute(&self) -> *const Option<Atom>;
-    fn style_attribute(&self) -> *const Option<Arc<RwLock<PropertyDeclarationBlock>>>;
+    fn style_attribute(&self) -> *const Option<Arc<Locked<PropertyDeclarationBlock>>>;
     fn local_name(&self) -> &LocalName;
     fn namespace(&self) -> &Namespace;
     fn get_lang_for_layout(&self) -> String;
@@ -384,14 +384,18 @@ impl LayoutElementHelpers for LayoutJS<Element> {
         where V: Push<ApplicableDeclarationBlock>
     {
         #[inline]
-        fn from_declaration(declaration: PropertyDeclaration) -> ApplicableDeclarationBlock {
+        fn from_declaration(shared_lock: &SharedRwLock, declaration: PropertyDeclaration)
+                            -> ApplicableDeclarationBlock {
             ApplicableDeclarationBlock::from_declarations(
-                Arc::new(RwLock::new(PropertyDeclarationBlock::with_one(
+                Arc::new(shared_lock.wrap(PropertyDeclarationBlock::with_one(
                     declaration, Importance::Normal
                 ))),
                 CascadeLevel::PresHints)
         }
 
+        let document = self.upcast::<Node>().owner_doc_for_layout();
+        let shared_lock = document.style_shared_lock();
+
         let bgcolor = if let Some(this) = self.downcast::<HTMLBodyElement>() {
             this.get_background_color()
         } else if let Some(this) = self.downcast::<HTMLTableElement>() {
@@ -408,6 +412,7 @@ impl LayoutElementHelpers for LayoutJS<Element> {
 
         if let Some(color) = bgcolor {
             hints.push(from_declaration(
+                shared_lock,
                 PropertyDeclaration::BackgroundColor(
                     CSSColor { parsed: Color::RGBA(color), authored: None })));
         }
@@ -420,6 +425,7 @@ impl LayoutElementHelpers for LayoutJS<Element> {
 
         if let Some(url) = background {
             hints.push(from_declaration(
+                shared_lock,
                 PropertyDeclaration::BackgroundImage(
                     background_image::SpecifiedValue(vec![
                         background_image::single_value::SpecifiedValue(Some(
@@ -442,6 +448,7 @@ impl LayoutElementHelpers for LayoutJS<Element> {
 
         if let Some(color) = color {
             hints.push(from_declaration(
+                shared_lock,
                 PropertyDeclaration::Color(
                     longhands::color::SpecifiedValue(CSSColor {
                         parsed: Color::RGBA(color),
@@ -459,6 +466,7 @@ impl LayoutElementHelpers for LayoutJS<Element> {
 
         if let Some(font_family) = font_family {
             hints.push(from_declaration(
+                shared_lock,
                 PropertyDeclaration::FontFamily(
                         font_family::computed_value::T(vec![
                             font_family::computed_value::FontFamily::from_atom(
@@ -469,6 +477,7 @@ impl LayoutElementHelpers for LayoutJS<Element> {
 
         if let Some(font_size) = font_size {
             hints.push(from_declaration(
+                shared_lock,
                 PropertyDeclaration::FontSize(font_size::SpecifiedValue(font_size.into()))))
         }
 
@@ -481,6 +490,7 @@ impl LayoutElementHelpers for LayoutJS<Element> {
         if let Some(cellspacing) = cellspacing {
             let width_value = specified::Length::from_px(cellspacing as f32);
             hints.push(from_declaration(
+                shared_lock,
                 PropertyDeclaration::BorderSpacing(
                     Box::new(border_spacing::SpecifiedValue {
                         horizontal: width_value.clone(),
@@ -514,6 +524,7 @@ impl LayoutElementHelpers for LayoutJS<Element> {
         if let Some(size) = size {
             let value = specified::NoCalcLength::ServoCharacterWidth(specified::CharacterWidth(size));
             hints.push(from_declaration(
+                shared_lock,
                 PropertyDeclaration::Width(
                     specified::LengthOrPercentageOrAuto::Length(value))));
         }
@@ -539,12 +550,14 @@ impl LayoutElementHelpers for LayoutJS<Element> {
                 let width_value =
                     specified::LengthOrPercentageOrAuto::Percentage(specified::Percentage(percentage));
                 hints.push(from_declaration(
+                    shared_lock,
                     PropertyDeclaration::Width(width_value)));
             }
             LengthOrPercentageOrAuto::Length(length) => {
                 let width_value = specified::LengthOrPercentageOrAuto::Length(
                     specified::NoCalcLength::Absolute(length));
                 hints.push(from_declaration(
+                    shared_lock,
                     PropertyDeclaration::Width(width_value)));
             }
         }
@@ -564,12 +577,14 @@ impl LayoutElementHelpers for LayoutJS<Element> {
                 let height_value =
                     specified::LengthOrPercentageOrAuto::Percentage(specified::Percentage(percentage));
                 hints.push(from_declaration(
+                    shared_lock,
                     PropertyDeclaration::Height(height_value)));
             }
             LengthOrPercentageOrAuto::Length(length) => {
                 let height_value = specified::LengthOrPercentageOrAuto::Length(
                     specified::NoCalcLength::Absolute(length));
                 hints.push(from_declaration(
+                    shared_lock,
                     PropertyDeclaration::Height(height_value)));
             }
         }
@@ -592,6 +607,7 @@ impl LayoutElementHelpers for LayoutJS<Element> {
             // https://html.spec.whatwg.org/multipage/#textarea-effective-width
             let value = specified::NoCalcLength::ServoCharacterWidth(specified::CharacterWidth(cols));
             hints.push(from_declaration(
+                shared_lock,
                 PropertyDeclaration::Width(specified::LengthOrPercentageOrAuto::Length(value))));
         }
 
@@ -610,6 +626,7 @@ impl LayoutElementHelpers for LayoutJS<Element> {
             // https://html.spec.whatwg.org/multipage/#textarea-effective-height
             let value = specified::NoCalcLength::FontRelative(specified::FontRelativeLength::Em(rows as CSSFloat));
             hints.push(from_declaration(
+                shared_lock,
                 PropertyDeclaration::Height(specified::LengthOrPercentageOrAuto::Length(value))));
         }
 
@@ -623,12 +640,16 @@ impl LayoutElementHelpers for LayoutJS<Element> {
         if let Some(border) = border {
             let width_value = specified::BorderWidth::from_length(specified::Length::from_px(border as f32));
             hints.push(from_declaration(
+                shared_lock,
                 PropertyDeclaration::BorderTopWidth(Box::new(width_value.clone()))));
             hints.push(from_declaration(
+                shared_lock,
                 PropertyDeclaration::BorderLeftWidth(Box::new(width_value.clone()))));
             hints.push(from_declaration(
+                shared_lock,
                 PropertyDeclaration::BorderBottomWidth(Box::new(width_value.clone()))));
             hints.push(from_declaration(
+                shared_lock,
                 PropertyDeclaration::BorderRightWidth(Box::new(width_value))));
         }
     }
@@ -672,7 +693,7 @@ impl LayoutElementHelpers for LayoutJS<Element> {
     }
 
     #[allow(unsafe_code)]
-    fn style_attribute(&self) -> *const Option<Arc<RwLock<PropertyDeclarationBlock>>> {
+    fn style_attribute(&self) -> *const Option<Arc<Locked<PropertyDeclarationBlock>>> {
         unsafe {
             (*self.unsafe_get()).style_attribute.borrow_for_layout()
         }
@@ -835,7 +856,7 @@ impl Element {
         ns!()
     }
 
-    pub fn style_attribute(&self) -> &DOMRefCell<Option<Arc<RwLock<PropertyDeclarationBlock>>>> {
+    pub fn style_attribute(&self) -> &DOMRefCell<Option<Arc<Locked<PropertyDeclarationBlock>>>> {
         &self.style_attribute
     }
 
@@ -2170,7 +2191,7 @@ impl VirtualMethods for Element {
                             block
                         } else {
                             let win = window_from_node(self);
-                            Arc::new(RwLock::new(parse_style_attribute(
+                            Arc::new(doc.style_shared_lock().wrap(parse_style_attribute(
                                 &attr.value(),
                                 &doc.base_url(),
                                 win.css_error_reporter(),
diff --git a/components/script/layout_wrapper.rs b/components/script/layout_wrapper.rs
index 5a9a834667b..36aa7601d0b 100644
--- a/components/script/layout_wrapper.rs
+++ b/components/script/layout_wrapper.rs
@@ -44,7 +44,6 @@ use dom::text::Text;
 use gfx_traits::ByteIndex;
 use html5ever_atoms::{LocalName, Namespace};
 use msg::constellation_msg::PipelineId;
-use parking_lot::RwLock;
 use range::Range;
 use script_layout_interface::{HTMLCanvasData, LayoutNodeType, SVGSVGData, TrustedNodeAddress};
 use script_layout_interface::{OpaqueStyleAndLayoutData, PartialPersistentLayoutData};
@@ -69,7 +68,7 @@ use style::dom::UnsafeNode;
 use style::element_state::*;
 use style::properties::{ComputedValues, PropertyDeclarationBlock};
 use style::selector_parser::{NonTSPseudoClass, PseudoElement, SelectorImpl};
-use style::shared_lock::SharedRwLock as StyleSharedRwLock;
+use style::shared_lock::{SharedRwLock as StyleSharedRwLock, Locked as StyleLocked};
 use style::sink::Push;
 use style::str::is_whitespace;
 use style::stylist::ApplicableDeclarationBlock;
@@ -377,7 +376,7 @@ impl<'le> TElement for ServoLayoutElement<'le> {
         ServoLayoutNode::from_layout_js(self.element.upcast())
     }
 
-    fn style_attribute(&self) -> Option<&Arc<RwLock<PropertyDeclarationBlock>>> {
+    fn style_attribute(&self) -> Option<&Arc<StyleLocked<PropertyDeclarationBlock>>> {
         unsafe {
             (*self.element.style_attribute()).as_ref()
         }
diff --git a/components/style/Cargo.toml b/components/style/Cargo.toml
index c1c234c994a..6532efc4e9d 100644
--- a/components/style/Cargo.toml
+++ b/components/style/Cargo.toml
@@ -13,7 +13,7 @@ path = "lib.rs"
 doctest = false
 
 [features]
-gecko = ["nsstring_vendor", "rayon/unstable"]
+gecko = ["nsstring_vendor", "rayon/unstable", "num_cpus"]
 use_bindgen = ["bindgen", "regex"]
 servo = ["serde/unstable", "serde", "serde_derive", "heapsize_derive",
          "style_traits/servo", "servo_atoms", "html5ever-atoms",
@@ -37,6 +37,7 @@ lazy_static = "0.2"
 log = "0.3"
 matches = "0.1"
 nsstring_vendor = {path = "gecko_bindings/nsstring_vendor", optional = true}
+num_cpus = {version = "1.1.0", optional = true}
 num-integer = "0.1.32"
 num-traits = "0.1.32"
 ordered-float = "0.4"
diff --git a/components/style/animation.rs b/components/style/animation.rs
index ddf1498d983..9734b67c1fd 100644
--- a/components/style/animation.rs
+++ b/components/style/animation.rs
@@ -415,7 +415,7 @@ fn compute_style_for_animation_step(context: &SharedStyleContext,
     match step.value {
         KeyframesStepValue::ComputedValues => style_from_cascade.clone(),
         KeyframesStepValue::Declarations { block: ref declarations } => {
-            let guard = declarations.read();
+            let guard = declarations.read_with(context.guards.author);
 
             // No !important in keyframes.
             debug_assert!(guard.declarations().iter()
diff --git a/components/style/attr.rs b/components/style/attr.rs
index 0d07a35e828..b4cd434635e 100644
--- a/components/style/attr.rs
+++ b/components/style/attr.rs
@@ -11,9 +11,9 @@ use app_units::Au;
 use cssparser::{self, Color, RGBA};
 use euclid::num::Zero;
 use num_traits::ToPrimitive;
-use parking_lot::RwLock;
 use properties::PropertyDeclarationBlock;
 use servo_url::ServoUrl;
+use shared_lock::Locked;
 use std::ascii::AsciiExt;
 use std::str::FromStr;
 use std::sync::Arc;
@@ -61,7 +61,7 @@ pub enum AttrValue {
     /// declarationblock for longer than needed.
     Declaration(String,
                 #[cfg_attr(feature = "servo", ignore_heap_size_of = "Arc")]
-                Arc<RwLock<PropertyDeclarationBlock>>)
+                Arc<Locked<PropertyDeclarationBlock>>)
 }
 
 /// Shared implementation to parse an integer according to
diff --git a/components/style/dom.rs b/components/style/dom.rs
index 612105c20e9..ac8ad3bd109 100644
--- a/components/style/dom.rs
+++ b/components/style/dom.rs
@@ -11,10 +11,10 @@ use {Atom, Namespace, LocalName};
 use atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
 use data::ElementData;
 use element_state::ElementState;
-use parking_lot::RwLock;
 use properties::{ComputedValues, PropertyDeclarationBlock};
 use selector_parser::{ElementExt, PreExistingComputedValues, PseudoElement};
 use selectors::matching::ElementSelectorFlags;
+use shared_lock::Locked;
 use sink::Push;
 use std::fmt;
 use std::fmt::Debug;
@@ -230,8 +230,8 @@ pub trait PresentationalHintsSynthetizer {
 
 /// The animation rules. The first one is for Animation cascade level, and the second one is for
 /// Transition cascade level.
-pub struct AnimationRules(pub Option<Arc<RwLock<PropertyDeclarationBlock>>>,
-                          pub Option<Arc<RwLock<PropertyDeclarationBlock>>>);
+pub struct AnimationRules(pub Option<Arc<Locked<PropertyDeclarationBlock>>>,
+                          pub Option<Arc<Locked<PropertyDeclarationBlock>>>);
 
 /// The element trait, the main abstraction the style crate acts over.
 pub trait TElement : PartialEq + Debug + Sized + Copy + Clone + ElementExt + PresentationalHintsSynthetizer {
@@ -252,7 +252,7 @@ pub trait TElement : PartialEq + Debug + Sized + Copy + Clone + ElementExt + Pre
     }
 
     /// Get this element's style attribute.
-    fn style_attribute(&self) -> Option<&Arc<RwLock<PropertyDeclarationBlock>>>;
+    fn style_attribute(&self) -> Option<&Arc<Locked<PropertyDeclarationBlock>>>;
 
     /// Get this element's animation rules.
     fn get_animation_rules(&self, _pseudo: Option<&PseudoElement>) -> AnimationRules {
@@ -261,13 +261,13 @@ pub trait TElement : PartialEq + Debug + Sized + Copy + Clone + ElementExt + Pre
 
     /// Get this element's animation rule.
     fn get_animation_rule(&self, _pseudo: Option<&PseudoElement>)
-                          -> Option<Arc<RwLock<PropertyDeclarationBlock>>> {
+                          -> Option<Arc<Locked<PropertyDeclarationBlock>>> {
         None
     }
 
     /// Get this element's transition rule.
     fn get_transition_rule(&self, _pseudo: Option<&PseudoElement>)
-                           -> Option<Arc<RwLock<PropertyDeclarationBlock>>> {
+                           -> Option<Arc<Locked<PropertyDeclarationBlock>>> {
         None
     }
 
diff --git a/components/style/gecko/arc_types.rs b/components/style/gecko/arc_types.rs
index d400c01c568..349fca1bbcb 100644
--- a/components/style/gecko/arc_types.rs
+++ b/components/style/gecko/arc_types.rs
@@ -48,7 +48,7 @@ impl_arc_ffi!(Stylesheet => RawServoStyleSheet
 impl_arc_ffi!(ComputedValues => ServoComputedValues
               [Servo_ComputedValues_AddRef, Servo_ComputedValues_Release]);
 
-impl_arc_ffi!(RwLock<PropertyDeclarationBlock> => RawServoDeclarationBlock
+impl_arc_ffi!(Locked<PropertyDeclarationBlock> => RawServoDeclarationBlock
               [Servo_DeclarationBlock_AddRef, Servo_DeclarationBlock_Release]);
 
 impl_arc_ffi!(Locked<StyleRule> => RawServoStyleRule
diff --git a/components/style/gecko/global_style_data.rs b/components/style/gecko/global_style_data.rs
new file mode 100644
index 00000000000..2653ad16b1f
--- /dev/null
+++ b/components/style/gecko/global_style_data.rs
@@ -0,0 +1,50 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Global style data
+
+use num_cpus;
+use rayon;
+use shared_lock::SharedRwLock;
+use std::cmp;
+use std::env;
+
+/// Global style data
+pub struct GlobalStyleData {
+    /// How many threads parallel styling can use.
+    pub num_threads: usize,
+
+    /// The parallel styling thread pool.
+    pub style_thread_pool: Option<rayon::ThreadPool>,
+
+    /// Shared RWLock for CSSOM objects
+    pub shared_lock: SharedRwLock,
+}
+
+lazy_static! {
+    /// Global style data
+    pub static ref GLOBAL_STYLE_DATA: GlobalStyleData = {
+        let stylo_threads = env::var("STYLO_THREADS")
+            .map(|s| s.parse::<usize>().expect("invalid STYLO_THREADS value"));
+        let num_threads = match stylo_threads {
+            Ok(num) => num,
+            _ => cmp::max(num_cpus::get() * 3 / 4, 1),
+        };
+
+        let pool = if num_threads <= 1 {
+            None
+        } else {
+            let configuration =
+                rayon::Configuration::new().set_num_threads(num_threads);
+            let pool = rayon::ThreadPool::new(configuration).ok();
+            pool
+        };
+
+        GlobalStyleData {
+            num_threads: num_threads,
+            style_thread_pool: pool,
+            shared_lock: SharedRwLock::new(),
+        }
+    };
+}
diff --git a/components/style/gecko/mod.rs b/components/style/gecko/mod.rs
index 2ee19fc60fc..48d50c5fa80 100644
--- a/components/style/gecko/mod.rs
+++ b/components/style/gecko/mod.rs
@@ -10,6 +10,7 @@ mod non_ts_pseudo_class_list;
 pub mod arc_types;
 pub mod conversions;
 pub mod data;
+pub mod global_style_data;
 pub mod media_queries;
 pub mod restyle_damage;
 pub mod selector_parser;
diff --git a/components/style/gecko/wrapper.rs b/components/style/gecko/wrapper.rs
index fa057a4ae26..b9cab601f2c 100644
--- a/components/style/gecko/wrapper.rs
+++ b/components/style/gecko/wrapper.rs
@@ -20,6 +20,7 @@ use dom::{AnimationRules, LayoutIterator, NodeInfo, TElement, TNode, UnsafeNode}
 use dom::{OpaqueNode, PresentationalHintsSynthetizer};
 use element_state::ElementState;
 use error_reporting::StdoutErrorReporter;
+use gecko::global_style_data::GLOBAL_STYLE_DATA;
 use gecko::selector_parser::{SelectorImpl, NonTSPseudoClass, PseudoElement};
 use gecko::snapshot_helpers;
 use gecko_bindings::bindings;
@@ -53,6 +54,7 @@ use selectors::Element;
 use selectors::matching::{ElementSelectorFlags, StyleRelations, matches_complex_selector};
 use selectors::parser::{AttrSelector, NamespaceConstraint};
 use servo_url::ServoUrl;
+use shared_lock::Locked;
 use sink::Push;
 use std::fmt;
 use std::ptr;
@@ -407,12 +409,14 @@ fn selector_flags_to_node_flags(flags: ElementSelectorFlags) -> u32 {
 fn get_animation_rule(element: &GeckoElement,
                       pseudo: Option<&PseudoElement>,
                       cascade_level: CascadeLevel)
-                      -> Option<Arc<RwLock<PropertyDeclarationBlock>>> {
+                      -> Option<Arc<Locked<PropertyDeclarationBlock>>> {
     let atom_ptr = PseudoElement::ns_atom_or_null_from_opt(pseudo);
     let animation_values = Arc::new(RwLock::new(AnimationValueMap::new()));
     if unsafe { Gecko_GetAnimationRule(element.0, atom_ptr, cascade_level,
                                        HasArcFFI::arc_as_borrowed(&animation_values)) } {
-        Some(Arc::new(RwLock::new(PropertyDeclarationBlock::from_animation_value_map(&animation_values.read()))))
+        let shared_lock = &GLOBAL_STYLE_DATA.shared_lock;
+        Some(Arc::new(shared_lock.wrap(
+            PropertyDeclarationBlock::from_animation_value_map(&animation_values.read()))))
     } else {
         None
     }
@@ -425,7 +429,7 @@ impl<'le> TElement for GeckoElement<'le> {
         unsafe { GeckoNode(&*(self.0 as *const _ as *const RawGeckoNode)) }
     }
 
-    fn style_attribute(&self) -> Option<&Arc<RwLock<PropertyDeclarationBlock>>> {
+    fn style_attribute(&self) -> Option<&Arc<Locked<PropertyDeclarationBlock>>> {
         let declarations = unsafe { Gecko_GetStyleAttrDeclarationBlock(self.0) };
         declarations.map(|s| s.as_arc_opt()).unwrap_or(None)
     }
@@ -436,12 +440,12 @@ impl<'le> TElement for GeckoElement<'le> {
     }
 
     fn get_animation_rule(&self, pseudo: Option<&PseudoElement>)
-                          -> Option<Arc<RwLock<PropertyDeclarationBlock>>> {
+                          -> Option<Arc<Locked<PropertyDeclarationBlock>>> {
         get_animation_rule(self, pseudo, CascadeLevel::Animations)
     }
 
     fn get_transition_rule(&self, pseudo: Option<&PseudoElement>)
-                           -> Option<Arc<RwLock<PropertyDeclarationBlock>>> {
+                           -> Option<Arc<Locked<PropertyDeclarationBlock>>> {
         get_animation_rule(self, pseudo, CascadeLevel::Transitions)
     }
 
diff --git a/components/style/keyframes.rs b/components/style/keyframes.rs
index 44ca0921706..67f0c848f8d 100644
--- a/components/style/keyframes.rs
+++ b/components/style/keyframes.rs
@@ -8,14 +8,13 @@
 
 use cssparser::{AtRuleParser, Parser, QualifiedRuleParser, RuleListParser};
 use cssparser::{DeclarationListParser, DeclarationParser, parse_one_rule};
-use parking_lot::RwLock;
 use parser::{ParserContext, ParserContextExtraData, log_css_error};
 use properties::{Importance, PropertyDeclaration, PropertyDeclarationBlock, PropertyId};
 use properties::{PropertyDeclarationId, LonghandId, ParsedDeclaration};
 use properties::LonghandIdSet;
 use properties::animated_properties::TransitionProperty;
 use properties::longhands::transition_timing_function::single_value::SpecifiedValue as SpecifiedTimingFunction;
-use shared_lock::{SharedRwLock, SharedRwLockReadGuard, Locked};
+use shared_lock::{SharedRwLock, SharedRwLockReadGuard, Locked, ToCssWithGuard};
 use std::fmt;
 use std::sync::Arc;
 use style_traits::ToCss;
@@ -102,11 +101,12 @@ pub struct Keyframe {
     ///
     /// Note that `!important` rules in keyframes don't apply, but we keep this
     /// `Arc` just for convenience.
-    pub block: Arc<RwLock<PropertyDeclarationBlock>>,
+    pub block: Arc<Locked<PropertyDeclarationBlock>>,
 }
 
-impl ToCss for Keyframe {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+impl ToCssWithGuard for Keyframe {
+    fn to_css<W>(&self, guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
+    where W: fmt::Write {
         let mut iter = self.selector.percentages().iter();
         try!(iter.next().unwrap().to_css(dest));
         for percentage in iter {
@@ -114,7 +114,7 @@ impl ToCss for Keyframe {
             try!(percentage.to_css(dest));
         }
         try!(dest.write_str(" { "));
-        try!(self.block.read().to_css(dest));
+        try!(self.block.read_with(guard).to_css(dest));
         try!(dest.write_str(" }"));
         Ok(())
     }
@@ -154,7 +154,7 @@ pub enum KeyframesStepValue {
     Declarations {
         /// The declaration block per se.
         #[cfg_attr(feature = "servo", ignore_heap_size_of = "Arc")]
-        block: Arc<RwLock<PropertyDeclarationBlock>>
+        block: Arc<Locked<PropertyDeclarationBlock>>
     },
     /// A synthetic step computed from the current computed values at the time
     /// of the animation.
@@ -180,10 +180,11 @@ pub struct KeyframesStep {
 impl KeyframesStep {
     #[inline]
     fn new(percentage: KeyframePercentage,
-           value: KeyframesStepValue) -> Self {
+           value: KeyframesStepValue,
+           guard: &SharedRwLockReadGuard) -> Self {
         let declared_timing_function = match value {
             KeyframesStepValue::Declarations { ref block } => {
-                block.read().declarations().iter().any(|&(ref prop_decl, _)| {
+                block.read_with(guard).declarations().iter().any(|&(ref prop_decl, _)| {
                     match *prop_decl {
                         PropertyDeclaration::AnimationTimingFunction(..) => true,
                         _ => false,
@@ -201,13 +202,14 @@ impl KeyframesStep {
     }
 
     /// Return specified TransitionTimingFunction if this KeyframesSteps has 'animation-timing-function'.
-    pub fn get_animation_timing_function(&self) -> Option<SpecifiedTimingFunction> {
+    pub fn get_animation_timing_function(&self, guard: &SharedRwLockReadGuard)
+                                         -> Option<SpecifiedTimingFunction> {
         if !self.declared_timing_function {
             return None;
         }
         match self.value {
             KeyframesStepValue::Declarations { ref block } => {
-                let guard = block.read();
+                let guard = block.read_with(guard);
                 let &(ref declaration, _) =
                     guard.get(PropertyDeclarationId::Longhand(LonghandId::AnimationTimingFunction)).unwrap();
                 match *declaration {
@@ -249,7 +251,8 @@ fn get_animated_properties(keyframes: &[Arc<Locked<Keyframe>>], guard: &SharedRw
     // it here.
     for keyframe in keyframes {
         let keyframe = keyframe.read_with(&guard);
-        for &(ref declaration, importance) in keyframe.block.read().declarations().iter() {
+        let block = keyframe.block.read_with(guard);
+        for &(ref declaration, importance) in block.declarations().iter() {
             assert!(!importance.important());
 
             if let Some(property) = TransitionProperty::from_declaration(declaration) {
@@ -294,7 +297,7 @@ impl KeyframesAnimation {
             for percentage in keyframe.selector.0.iter() {
                 result.steps.push(KeyframesStep::new(*percentage, KeyframesStepValue::Declarations {
                     block: keyframe.block.clone(),
-                }));
+                }, guard));
             }
         }
 
@@ -304,12 +307,14 @@ impl KeyframesAnimation {
         // Prepend autogenerated keyframes if appropriate.
         if result.steps[0].start_percentage.0 != 0. {
             result.steps.insert(0, KeyframesStep::new(KeyframePercentage::new(0.),
-                                                      KeyframesStepValue::ComputedValues));
+                                                      KeyframesStepValue::ComputedValues,
+                                                      guard));
         }
 
         if result.steps.last().unwrap().start_percentage.0 != 1. {
             result.steps.push(KeyframesStep::new(KeyframePercentage::new(1.),
-                                                 KeyframesStepValue::ComputedValues));
+                                                 KeyframesStepValue::ComputedValues,
+                                                 guard));
         }
 
         result
@@ -381,7 +386,7 @@ impl<'a> QualifiedRuleParser for KeyframeListParser<'a> {
         }
         Ok(Arc::new(self.shared_lock.wrap(Keyframe {
             selector: prelude,
-            block: Arc::new(RwLock::new(block)),
+            block: Arc::new(self.shared_lock.wrap(block)),
         })))
     }
 }
diff --git a/components/style/lib.rs b/components/style/lib.rs
index eabb8d20c51..ab564c59bd8 100644
--- a/components/style/lib.rs
+++ b/components/style/lib.rs
@@ -57,6 +57,7 @@ extern crate log;
 #[macro_use]
 extern crate matches;
 #[cfg(feature = "gecko")] extern crate nsstring_vendor as nsstring;
+#[cfg(feature = "gecko")] extern crate num_cpus;
 extern crate num_integer;
 extern crate num_traits;
 extern crate ordered_float;
diff --git a/components/style/matching.rs b/components/style/matching.rs
index f58d429beb0..38552ff46da 100644
--- a/components/style/matching.rs
+++ b/components/style/matching.rs
@@ -886,7 +886,8 @@ pub trait MatchMethods : TElement {
             let new_node = context.shared.stylist.rule_tree
                 .update_rule_at_level(CascadeLevel::StyleAttributeNormal,
                                       style_attribute,
-                                      primary_rules);
+                                      primary_rules,
+                                      &context.shared.guards);
             if let Some(n) = new_node {
                 *primary_rules = n;
                 rule_node_changed = true;
@@ -895,7 +896,8 @@ pub trait MatchMethods : TElement {
             let new_node = context.shared.stylist.rule_tree
                 .update_rule_at_level(CascadeLevel::StyleAttributeImportant,
                                       style_attribute,
-                                      primary_rules);
+                                      primary_rules,
+                                      &context.shared.guards);
             if let Some(n) = new_node {
                 *primary_rules = n;
                 rule_node_changed = true;
diff --git a/components/style/rule_tree/mod.rs b/components/style/rule_tree/mod.rs
index c1d4b27edf5..80aa88596d6 100644
--- a/components/style/rule_tree/mod.rs
+++ b/components/style/rule_tree/mod.rs
@@ -10,7 +10,6 @@
 use arc_ptr_eq;
 #[cfg(feature = "servo")]
 use heapsize::HeapSizeOf;
-use parking_lot::{RwLock, RwLockReadGuard};
 use properties::{Importance, PropertyDeclarationBlock};
 use shared_lock::{Locked, ReadGuards, SharedRwLockReadGuard};
 use std::io::{self, Write};
@@ -54,7 +53,7 @@ pub enum StyleSource {
     /// A style rule stable pointer.
     Style(Arc<Locked<StyleRule>>),
     /// A declaration block stable pointer.
-    Declarations(Arc<RwLock<PropertyDeclarationBlock>>),
+    Declarations(Arc<Locked<PropertyDeclarationBlock>>),
 }
 
 impl StyleSource {
@@ -82,13 +81,12 @@ impl StyleSource {
     /// Read the style source guard, and obtain thus read access to the
     /// underlying property declaration block.
     #[inline]
-    pub fn read<'a>(&'a self, guard: &'a SharedRwLockReadGuard)
-                    -> RwLockReadGuard<'a, PropertyDeclarationBlock> {
+    pub fn read<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> &'a PropertyDeclarationBlock {
         let block = match *self {
             StyleSource::Style(ref rule) => &rule.read_with(guard).block,
             StyleSource::Declarations(ref block) => block,
         };
-        block.read()
+        block.read_with(guard)
     }
 }
 
@@ -162,8 +160,9 @@ impl RuleTree {
     /// the old path is still valid.
     pub fn update_rule_at_level(&self,
                                 level: CascadeLevel,
-                                pdb: Option<&Arc<RwLock<PropertyDeclarationBlock>>>,
-                                path: &StrongRuleNode)
+                                pdb: Option<&Arc<Locked<PropertyDeclarationBlock>>>,
+                                path: &StrongRuleNode,
+                                guards: &ReadGuards)
                                 -> Option<StrongRuleNode> {
         debug_assert!(level.is_unique_per_element());
         // TODO(emilio): Being smarter with lifetimes we could avoid a bit of
@@ -222,13 +221,13 @@ impl RuleTree {
         // pretty bad styling cases already.
         if let Some(pdb) = pdb {
             if level.is_important() {
-                if pdb.read().any_important() {
+                if pdb.read_with(level.guard(guards)).any_important() {
                     current = current.ensure_child(self.root.downgrade(),
                                                    StyleSource::Declarations(pdb.clone()),
                                                    level);
                 }
             } else {
-                if pdb.read().any_normal() {
+                if pdb.read_with(level.guard(guards)).any_normal() {
                     current = current.ensure_child(self.root.downgrade(),
                                                    StyleSource::Declarations(pdb.clone()),
                                                    level);
diff --git a/components/style/stylesheets.rs b/components/style/stylesheets.rs
index 96c553c4a49..95104a4df60 100644
--- a/components/style/stylesheets.rs
+++ b/components/style/stylesheets.rs
@@ -469,7 +469,7 @@ impl ToCssWithGuard for KeyframesRule {
             }
             first = false;
             let keyframe = lock.read_with(&guard);
-            try!(keyframe.to_css(dest));
+            try!(keyframe.to_css(guard, dest));
         }
         dest.write_str(" }")
     }
@@ -528,19 +528,19 @@ impl ToCssWithGuard for SupportsRule {
 #[derive(Debug)]
 pub struct StyleRule {
     pub selectors: SelectorList<SelectorImpl>,
-    pub block: Arc<RwLock<PropertyDeclarationBlock>>,
+    pub block: Arc<Locked<PropertyDeclarationBlock>>,
 }
 
 impl ToCssWithGuard for StyleRule {
     // https://drafts.csswg.org/cssom/#serialize-a-css-rule CSSStyleRule
-    fn to_css<W>(&self, _guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
+    fn to_css<W>(&self, guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result
     where W: fmt::Write {
         // Step 1
         try!(self.selectors.to_css(dest));
         // Step 2
         try!(dest.write_str(" { "));
         // Step 3
-        let declaration_block = self.block.read();
+        let declaration_block = self.block.read_with(guard);
         try!(declaration_block.to_css(dest));
         // Step 4
         if declaration_block.declarations().len() > 0 {
@@ -1018,9 +1018,10 @@ impl<'a, 'b> QualifiedRuleParser for NestedRuleParser<'a, 'b> {
 
     fn parse_block(&mut self, prelude: SelectorList<SelectorImpl>, input: &mut Parser)
                    -> Result<CssRule, ()> {
+        let declarations = parse_property_declaration_list(self.context, input);
         Ok(CssRule::Style(Arc::new(self.shared_lock.wrap(StyleRule {
             selectors: prelude,
-            block: Arc::new(RwLock::new(parse_property_declaration_list(self.context, input)))
+            block: Arc::new(self.shared_lock.wrap(declarations))
         }))))
     }
 }
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index 2166e81946a..d58e0dd0e85 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -12,7 +12,6 @@ use dom::{AnimationRules, PresentationalHintsSynthetizer, TElement};
 use error_reporting::StdoutErrorReporter;
 use keyframes::KeyframesAnimation;
 use media_queries::Device;
-use parking_lot::RwLock;
 use pdqsort::sort_by;
 use properties::{self, CascadeFlags, ComputedValues};
 #[cfg(feature = "servo")]
@@ -542,7 +541,7 @@ impl Stylist {
                                         &self,
                                         element: &E,
                                         parent_bf: Option<&BloomFilter>,
-                                        style_attribute: Option<&Arc<RwLock<PropertyDeclarationBlock>>>,
+                                        style_attribute: Option<&Arc<Locked<PropertyDeclarationBlock>>>,
                                         animation_rules: AnimationRules,
                                         pseudo_element: Option<&PseudoElement>,
                                         guards: &ReadGuards,
@@ -613,7 +612,7 @@ impl Stylist {
 
             // Step 4: Normal style attributes.
             if let Some(sa) = style_attribute {
-                if sa.read().any_normal() {
+                if sa.read_with(guards.author).any_normal() {
                     relations |= AFFECTED_BY_STYLE_ATTRIBUTE;
                     Push::push(
                         applicable_declarations,
@@ -649,7 +648,7 @@ impl Stylist {
 
             // Step 7: `!important` style attributes.
             if let Some(sa) = style_attribute {
-                if sa.read().any_important() {
+                if sa.read_with(guards.author).any_important() {
                     relations |= AFFECTED_BY_STYLE_ATTRIBUTE;
                     Push::push(
                         applicable_declarations,
@@ -1005,7 +1004,7 @@ impl SelectorMap {
             if rule.selector.compound_selector.is_empty() &&
                rule.selector.next.is_none() {
                 let style_rule = rule.style_rule.read_with(guard);
-                let block = style_rule.block.read();
+                let block = style_rule.block.read_with(guard);
                 if block.any_normal() {
                     matching_rules_list.push(
                         rule.to_applicable_declaration_block(cascade_level));
@@ -1069,7 +1068,7 @@ impl SelectorMap {
     {
         for rule in rules.iter() {
             let style_rule = rule.style_rule.read_with(guard);
-            let block = style_rule.block.read();
+            let block = style_rule.block.read_with(guard);
             let any_declaration_for_importance = if cascade_level.is_important() {
                 block.any_important()
             } else {
@@ -1208,7 +1207,7 @@ impl ApplicableDeclarationBlock {
     /// Constructs an applicable declaration block from a given property
     /// declaration block and importance.
     #[inline]
-    pub fn from_declarations(declarations: Arc<RwLock<PropertyDeclarationBlock>>,
+    pub fn from_declarations(declarations: Arc<Locked<PropertyDeclarationBlock>>,
                              level: CascadeLevel)
                              -> Self {
         ApplicableDeclarationBlock {
diff --git a/ports/geckolib/Cargo.toml b/ports/geckolib/Cargo.toml
index 9ed52128eaf..40e9b7e65ad 100644
--- a/ports/geckolib/Cargo.toml
+++ b/ports/geckolib/Cargo.toml
@@ -20,9 +20,7 @@ env_logger = {version = "0.4", default-features = false} # disable `regex` to re
 lazy_static = "0.2"
 libc = "0.2"
 log = {version = "0.3.5", features = ["release_max_level_info"]}
-num_cpus = "1.1.0"
 parking_lot = "0.3"
-rayon = "0.6"
 selectors = {path = "../../components/selectors"}
 servo_url = {path = "../../components/url"}
 style = {path = "../../components/style", features = ["gecko"]}
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index bbe8bc6907d..f39e4a903cc 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -6,13 +6,10 @@ use atomic_refcell::AtomicRefMut;
 use cssparser::Parser;
 use cssparser::ToCss as ParserToCss;
 use env_logger::LogBuilder;
-use num_cpus;
 use parking_lot::RwLock;
-use rayon;
 use selectors::Element;
 use servo_url::ServoUrl;
 use std::borrow::Cow;
-use std::cmp;
 use std::env;
 use std::fmt::Write;
 use std::ptr;
@@ -24,6 +21,7 @@ use style::data::{ElementData, ElementStyles, RestyleData};
 use style::dom::{ShowSubtreeData, TElement, TNode};
 use style::error_reporting::StdoutErrorReporter;
 use style::gecko::data::{PerDocumentStyleData, PerDocumentStyleDataImpl};
+use style::gecko::global_style_data::GLOBAL_STYLE_DATA;
 use style::gecko::restyle_damage::GeckoRestyleDamage;
 use style::gecko::selector_parser::{SelectorImpl, PseudoElement};
 use style::gecko::traversal::RecalcStyleOnly;
@@ -96,48 +94,7 @@ use super::stylesheet_loader::StylesheetLoader;
  * depend on but good enough for our purposes.
  */
 
-pub struct GlobalStyleData {
-    // How many threads parallel styling can use.
-    pub num_threads: usize,
 
-    // The parallel styling thread pool.
-    pub style_thread_pool: Option<rayon::ThreadPool>,
-
-    // Shared RWLock for CSSOM objects
-    pub shared_lock: SharedRwLock,
-}
-
-impl GlobalStyleData {
-    pub fn new() -> Self {
-        let stylo_threads = env::var("STYLO_THREADS")
-            .map(|s| s.parse::<usize>().expect("invalid STYLO_THREADS value"));
-        let num_threads = match stylo_threads {
-            Ok(num) => num,
-            _ => cmp::max(num_cpus::get() * 3 / 4, 1),
-        };
-
-        let pool = if num_threads <= 1 {
-            None
-        } else {
-            let configuration =
-                rayon::Configuration::new().set_num_threads(num_threads);
-            let pool = rayon::ThreadPool::new(configuration).ok();
-            pool
-        };
-
-        GlobalStyleData {
-            num_threads: num_threads,
-            style_thread_pool: pool,
-            shared_lock: SharedRwLock::new(),
-        }
-    }
-}
-
-lazy_static! {
-    pub static ref GLOBAL_STYLE_DATA: GlobalStyleData = {
-        GlobalStyleData::new()
-    };
-}
 
 #[no_mangle]
 pub extern "C" fn Servo_Initialize() {
@@ -638,7 +595,7 @@ pub extern "C" fn Servo_StyleRule_SetStyle(rule: RawServoStyleRuleBorrowed,
     let global_style_data = &*GLOBAL_STYLE_DATA;
     let mut guard = global_style_data.shared_lock.write();
     let rule = Locked::<StyleRule>::as_arc(&rule);
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
     rule.write_with(&mut guard).block = declarations.clone();
 }
 
@@ -829,9 +786,10 @@ pub extern "C" fn Servo_ParseProperty(property: *const nsACString, value: *const
 
     match ParsedDeclaration::parse(id, &context, &mut Parser::new(value), false) {
         Ok(parsed) => {
+            let global_style_data = &*GLOBAL_STYLE_DATA;
             let mut block = PropertyDeclarationBlock::new();
             parsed.expand(|d| block.push(d, Importance::Normal));
-            Arc::new(RwLock::new(block)).into_strong()
+            Arc::new(global_style_data.shared_lock.wrap(block)).into_strong()
         }
         Err(_) => RawServoDeclarationBlockStrong::null()
     }
@@ -842,36 +800,47 @@ pub extern "C" fn Servo_ParseStyleAttribute(data: *const nsACString,
                                             base: *const nsACString,
                                             raw_extra_data: *const structs::GeckoParserExtraData)
                                             -> RawServoDeclarationBlockStrong {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
     let value = unsafe { data.as_ref().unwrap().as_str_unchecked() };
     make_context!((base, raw_extra_data) => (base_url, extra_data));
-    Arc::new(RwLock::new(GeckoElement::parse_style_attribute(value, &base_url, extra_data))).into_strong()
+    Arc::new(global_style_data.shared_lock.wrap(
+        GeckoElement::parse_style_attribute(value, &base_url, extra_data))).into_strong()
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_DeclarationBlock_CreateEmpty() -> RawServoDeclarationBlockStrong {
-    Arc::new(RwLock::new(PropertyDeclarationBlock::new())).into_strong()
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    Arc::new(global_style_data.shared_lock.wrap(PropertyDeclarationBlock::new())).into_strong()
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_DeclarationBlock_Clone(declarations: RawServoDeclarationBlockBorrowed)
                                                -> RawServoDeclarationBlockStrong {
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
-    Arc::new(RwLock::new(declarations.read().clone())).into_strong()
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
+    Arc::new(global_style_data.shared_lock.wrap(
+        declarations.read_with(&guard).clone()
+    )).into_strong()
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_DeclarationBlock_Equals(a: RawServoDeclarationBlockBorrowed,
                                                 b: RawServoDeclarationBlockBorrowed)
                                                 -> bool {
-    *RwLock::<PropertyDeclarationBlock>::as_arc(&a).read().declarations() ==
-    *RwLock::<PropertyDeclarationBlock>::as_arc(&b).read().declarations()
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    *Locked::<PropertyDeclarationBlock>::as_arc(&a).read_with(&guard).declarations() ==
+    *Locked::<PropertyDeclarationBlock>::as_arc(&b).read_with(&guard).declarations()
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_DeclarationBlock_GetCssText(declarations: RawServoDeclarationBlockBorrowed,
                                                     result: *mut nsAString) {
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
-    declarations.read().to_css(unsafe { result.as_mut().unwrap() }).unwrap();
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
+    declarations.read_with(&guard).to_css(unsafe { result.as_mut().unwrap() }).unwrap();
 }
 
 #[no_mangle]
@@ -880,9 +849,11 @@ pub extern "C" fn Servo_DeclarationBlock_SerializeOneValue(
     property_id: nsCSSPropertyID, buffer: *mut nsAString)
 {
     let property_id = get_property_id_from_nscsspropertyid!(property_id, ());
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
     let mut string = String::new();
-    let rv = declarations.read().single_value_to_css(&property_id, &mut string);
+    let rv = declarations.read_with(&guard).single_value_to_css(&property_id, &mut string);
     debug_assert!(rv.is_ok());
 
     write!(unsafe { &mut *buffer }, "{}", string).expect("Failed to copy string");
@@ -890,15 +861,19 @@ pub extern "C" fn Servo_DeclarationBlock_SerializeOneValue(
 
 #[no_mangle]
 pub extern "C" fn Servo_DeclarationBlock_Count(declarations: RawServoDeclarationBlockBorrowed) -> u32 {
-     let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
-     declarations.read().declarations().len() as u32
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
+    declarations.read_with(&guard).declarations().len() as u32
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_DeclarationBlock_GetNthProperty(declarations: RawServoDeclarationBlockBorrowed,
                                                         index: u32, result: *mut nsAString) -> bool {
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
-    if let Some(&(ref decl, _)) = declarations.read().declarations().get(index as usize) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
+    if let Some(&(ref decl, _)) = declarations.read_with(&guard).declarations().get(index as usize) {
         let result = unsafe { result.as_mut().unwrap() };
         decl.id().to_css(result).unwrap();
         true
@@ -919,8 +894,12 @@ macro_rules! get_property_id_from_property {
 
 fn get_property_value(declarations: RawServoDeclarationBlockBorrowed,
                       property_id: PropertyId, value: *mut nsAString) {
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
-    declarations.read().property_value_to_css(&property_id, unsafe { value.as_mut().unwrap() }).unwrap();
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
+    declarations.read_with(&guard)
+        .property_value_to_css(&property_id, unsafe { value.as_mut().unwrap() })
+        .unwrap();
 }
 
 #[no_mangle]
@@ -939,8 +918,10 @@ pub extern "C" fn Servo_DeclarationBlock_GetPropertyValueById(declarations: RawS
 pub extern "C" fn Servo_DeclarationBlock_GetPropertyIsImportant(declarations: RawServoDeclarationBlockBorrowed,
                                                                 property: *const nsACString) -> bool {
     let property_id = get_property_id_from_property!(property, false);
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
-    declarations.read().property_priority(&property_id).important()
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
+    declarations.read_with(&guard).property_priority(&property_id).important()
 }
 
 fn set_property(declarations: RawServoDeclarationBlockBorrowed, property_id: PropertyId,
@@ -951,7 +932,10 @@ fn set_property(declarations: RawServoDeclarationBlockBorrowed, property_id: Pro
     make_context!((base, data) => (base_url, extra_data));
     if let Ok(parsed) = parse_one_declaration(property_id, value, &base_url,
                                               &StdoutErrorReporter, extra_data) {
-        let mut declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations).write();
+        let global_style_data = &*GLOBAL_STYLE_DATA;
+        let mut guard = global_style_data.shared_lock.write();
+        let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations)
+            .write_with(&mut guard);
         let importance = if is_important { Importance::Important } else { Importance::Normal };
         let mut changed = false;
         parsed.expand(|decl| {
@@ -984,8 +968,10 @@ pub extern "C" fn Servo_DeclarationBlock_SetPropertyById(declarations: RawServoD
 }
 
 fn remove_property(declarations: RawServoDeclarationBlockBorrowed, property_id: PropertyId) {
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
-    declarations.write().remove_property(&property_id);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
+    declarations.write_with(&mut guard).remove_property(&property_id);
 }
 
 #[no_mangle]
@@ -1095,9 +1081,11 @@ pub extern "C" fn Servo_DeclarationBlock_PropertyIsSet(declarations:
                                                        property: nsCSSPropertyID)
         -> bool {
     use style::properties::PropertyDeclarationId;
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
     let long = get_longhand_from_id!(property, false);
-    declarations.read().get(PropertyDeclarationId::Longhand(long)).is_some()
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    declarations.read_with(&guard).get(PropertyDeclarationId::Longhand(long)).is_some()
 }
 
 #[no_mangle]
@@ -1110,12 +1098,14 @@ pub extern "C" fn Servo_DeclarationBlock_SetIdentStringValue(declarations:
     use style::properties::{PropertyDeclaration, LonghandId};
     use style::properties::longhands::_x_lang::computed_value::T as Lang;
 
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
     let long = get_longhand_from_id!(property);
     let prop = match_wrap_declared! { long,
         XLang => Lang(Atom::from(value)),
     };
-    declarations.write().push(prop, Importance::Normal);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    declarations.write_with(&mut guard).push(prop, Importance::Normal);
 }
 
 #[no_mangle]
@@ -1128,7 +1118,7 @@ pub extern "C" fn Servo_DeclarationBlock_SetKeywordValue(declarations:
     use style::properties::longhands;
     use style::values::specified::{BorderStyle, NoCalcLength};
 
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
     let long = get_longhand_from_id!(property);
     let value = value as u32;
 
@@ -1152,7 +1142,9 @@ pub extern "C" fn Servo_DeclarationBlock_SetKeywordValue(declarations:
         BorderBottomStyle => BorderStyle::from_gecko_keyword(value),
         BorderLeftStyle => BorderStyle::from_gecko_keyword(value),
     };
-    declarations.write().push(prop, Importance::Normal);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    declarations.write_with(&mut guard).push(prop, Importance::Normal);
 }
 
 #[no_mangle]
@@ -1162,12 +1154,14 @@ pub extern "C" fn Servo_DeclarationBlock_SetIntValue(declarations: RawServoDecla
     use style::properties::{PropertyDeclaration, LonghandId};
     use style::properties::longhands::_x_span::computed_value::T as Span;
 
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
     let long = get_longhand_from_id!(property);
     let prop = match_wrap_declared! { long,
         XSpan => Span(value),
     };
-    declarations.write().push(prop, Importance::Normal);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    declarations.write_with(&mut guard).push(prop, Importance::Normal);
 }
 
 #[no_mangle]
@@ -1180,7 +1174,7 @@ pub extern "C" fn Servo_DeclarationBlock_SetPixelValue(declarations:
     use style::values::specified::BorderWidth;
     use style::values::specified::length::NoCalcLength;
 
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
     let long = get_longhand_from_id!(property);
     let nocalc = NoCalcLength::from_px(value);
 
@@ -1206,7 +1200,9 @@ pub extern "C" fn Servo_DeclarationBlock_SetPixelValue(declarations:
             }
         ),
     };
-    declarations.write().push(prop, Importance::Normal);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    declarations.write_with(&mut guard).push(prop, Importance::Normal);
 }
 
 #[no_mangle]
@@ -1217,7 +1213,7 @@ pub extern "C" fn Servo_DeclarationBlock_SetPercentValue(declarations:
     use style::properties::{PropertyDeclaration, LonghandId};
     use style::values::specified::length::Percentage;
 
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
     let long = get_longhand_from_id!(property);
     let pc = Percentage(value);
 
@@ -1229,7 +1225,9 @@ pub extern "C" fn Servo_DeclarationBlock_SetPercentValue(declarations:
         MarginBottom => pc.into(),
         MarginLeft => pc.into(),
     };
-    declarations.write().push(prop, Importance::Normal);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    declarations.write_with(&mut guard).push(prop, Importance::Normal);
 }
 
 #[no_mangle]
@@ -1239,7 +1237,7 @@ pub extern "C" fn Servo_DeclarationBlock_SetAutoValue(declarations:
     use style::properties::{PropertyDeclaration, LonghandId};
     use style::values::specified::LengthOrPercentageOrAuto;
 
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
     let long = get_longhand_from_id!(property);
     let auto = LengthOrPercentageOrAuto::Auto;
 
@@ -1251,7 +1249,9 @@ pub extern "C" fn Servo_DeclarationBlock_SetAutoValue(declarations:
         MarginBottom => auto,
         MarginLeft => auto,
     };
-    declarations.write().push(prop, Importance::Normal);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    declarations.write_with(&mut guard).push(prop, Importance::Normal);
 }
 
 #[no_mangle]
@@ -1261,7 +1261,7 @@ pub extern "C" fn Servo_DeclarationBlock_SetCurrentColor(declarations:
     use style::properties::{PropertyDeclaration, LonghandId};
     use style::values::specified::{Color, CSSColor};
 
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
     let long = get_longhand_from_id!(property);
     let cc = CSSColor { parsed: Color::CurrentColor, authored: None };
 
@@ -1271,7 +1271,9 @@ pub extern "C" fn Servo_DeclarationBlock_SetCurrentColor(declarations:
         BorderBottomColor => cc,
         BorderLeftColor => cc,
     };
-    declarations.write().push(prop, Importance::Normal);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    declarations.write_with(&mut guard).push(prop, Importance::Normal);
 }
 
 #[no_mangle]
@@ -1284,7 +1286,7 @@ pub extern "C" fn Servo_DeclarationBlock_SetColorValue(declarations:
     use style::properties::longhands;
     use style::values::specified::{Color, CSSColor};
 
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
     let long = get_longhand_from_id!(property);
     let rgba = convert_nscolor_to_rgba(value);
     let color = CSSColor { parsed: Color::RGBA(rgba), authored: None };
@@ -1297,7 +1299,9 @@ pub extern "C" fn Servo_DeclarationBlock_SetColorValue(declarations:
         Color => longhands::color::SpecifiedValue(color),
         BackgroundColor => color,
     };
-    declarations.write().push(prop, Importance::Normal);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    declarations.write_with(&mut guard).push(prop, Importance::Normal);
 }
 
 #[no_mangle]
@@ -1308,13 +1312,15 @@ pub extern "C" fn Servo_DeclarationBlock_SetFontFamily(declarations:
     use style::properties::PropertyDeclaration;
     use style::properties::longhands::font_family::SpecifiedValue as FontFamily;
 
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
     let string = unsafe { (*value).to_string() };
     let mut parser = Parser::new(&string);
     if let Ok(family) = FontFamily::parse(&mut parser) {
         if parser.is_exhausted() {
+            let global_style_data = &*GLOBAL_STYLE_DATA;
+            let mut guard = global_style_data.shared_lock.write();
             let decl = PropertyDeclaration::FontFamily(family);
-            declarations.write().push(decl, Importance::Normal);
+            declarations.write_with(&mut guard).push(decl, Importance::Normal);
         }
     }
 }
@@ -1325,11 +1331,14 @@ pub extern "C" fn Servo_DeclarationBlock_SetTextDecorationColorOverride(declarat
     use style::properties::PropertyDeclaration;
     use style::properties::longhands::text_decoration_line;
 
-    let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+
+    let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
     let mut decoration = text_decoration_line::computed_value::none;
     decoration |= text_decoration_line::COLOR_OVERRIDE;
     let decl = PropertyDeclaration::TextDecorationLine(decoration);
-    declarations.write().push(decl, Importance::Normal);
+    declarations.write_with(&mut guard).push(decl, Importance::Normal);
 }
 
 #[no_mangle]
@@ -1523,6 +1532,11 @@ pub extern "C" fn Servo_GetComputedKeyframeValues(keyframes: RawGeckoKeyframeLis
     use style::properties::LonghandIdSet;
     use style::properties::declaration_block::Importance;
     use style::values::computed::Context;
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+
+
     let data = PerDocumentStyleData::from_ffi(raw_data).borrow();
 
     let style = ComputedValues::as_arc(&style);
@@ -1549,8 +1563,8 @@ pub extern "C" fn Servo_GetComputedKeyframeValues(keyframes: RawGeckoKeyframeLis
                                            .filter(|&property| !property.mServoDeclarationBlock.mRawPtr.is_null());
         for property in iter {
             let declarations = unsafe { &*property.mServoDeclarationBlock.mRawPtr.clone() };
-            let declarations = RwLock::<PropertyDeclarationBlock>::as_arc(&declarations);
-            let guard = declarations.read();
+            let declarations = Locked::<PropertyDeclarationBlock>::as_arc(&declarations);
+            let guard = declarations.read_with(&guard);
 
             let anim_iter = guard.declarations()
                             .iter()
@@ -1614,15 +1628,18 @@ pub extern "C" fn Servo_StyleSet_FillKeyframesForName(raw_data: RawServoStyleSet
     use style::gecko_bindings::structs::Keyframe;
     use style::properties::LonghandIdSet;
 
+
     let data = PerDocumentStyleData::from_ffi(raw_data).borrow();
     let name = unsafe { Atom::from(name.as_ref().unwrap().as_str_unchecked()) };
     let style_timing_function = unsafe { timing_function.as_ref().unwrap() };
     let style = ComputedValues::as_arc(&style);
 
     if let Some(ref animation) = data.stylist.animations().get(&name) {
+       let global_style_data = &*GLOBAL_STYLE_DATA;
+       let guard = global_style_data.shared_lock.read();
        for step in &animation.steps {
           // Override timing_function if the keyframe has animation-timing-function.
-          let timing_function = if let Some(val) = step.get_animation_timing_function() {
+          let timing_function = if let Some(val) = step.get_animation_timing_function(&guard) {
               val.into()
           } else {
               *style_timing_function
@@ -1637,7 +1654,8 @@ pub extern "C" fn Servo_StyleSet_FillKeyframesForName(raw_data: RawServoStyleSet
           fn add_computed_property_value(keyframe: *mut Keyframe,
                                          index: usize,
                                          style: &ComputedValues,
-                                         property: &TransitionProperty) {
+                                         property: &TransitionProperty,
+                                         shared_lock: &SharedRwLock) {
               let block = style.to_declaration_block(property.clone().into());
               unsafe {
                   (*keyframe).mPropertyValues.set_len((index + 1) as u32);
@@ -1645,18 +1663,19 @@ pub extern "C" fn Servo_StyleSet_FillKeyframesForName(raw_data: RawServoStyleSet
                   // FIXME. Do not set computed values once we handles missing keyframes
                   // with additive composition.
                   (*keyframe).mPropertyValues[index].mServoDeclarationBlock.set_arc_leaky(
-                      Arc::new(RwLock::new(block)));
+                      Arc::new(shared_lock.wrap(block)));
               }
           }
 
           match step.value {
               KeyframesStepValue::ComputedValues => {
                   for (index, property) in animation.properties_changed.iter().enumerate() {
-                      add_computed_property_value(keyframe, index, style, property);
+                      add_computed_property_value(
+                          keyframe, index, style, property, &global_style_data.shared_lock);
                   }
               },
               KeyframesStepValue::Declarations { ref block } => {
-                  let guard = block.read();
+                  let guard = block.read_with(&guard);
                   // Filter out non-animatable properties.
                   let animatable =
                       guard.declarations()
@@ -1673,8 +1692,9 @@ pub extern "C" fn Servo_StyleSet_FillKeyframesForName(raw_data: RawServoStyleSet
                           (*keyframe).mPropertyValues.set_len((index + 1) as u32);
                           (*keyframe).mPropertyValues[index].mProperty = property.into();
                           (*keyframe).mPropertyValues[index].mServoDeclarationBlock.set_arc_leaky(
-                              Arc::new(RwLock::new(PropertyDeclarationBlock::with_one(
-                                declaration.clone(), Importance::Normal
+                              Arc::new(global_style_data.shared_lock.wrap(
+                                PropertyDeclarationBlock::with_one(
+                                    declaration.clone(), Importance::Normal
                               ))));
                           if step.start_percentage.0 == 0. ||
                              step.start_percentage.0 == 1. {
@@ -1689,7 +1709,8 @@ pub extern "C" fn Servo_StyleSet_FillKeyframesForName(raw_data: RawServoStyleSet
                       let mut index = unsafe { (*keyframe).mPropertyValues.len() };
                       for property in animation.properties_changed.iter() {
                           if !seen.has_transition_property_bit(&property) {
-                              add_computed_property_value(keyframe, index, style, property);
+                              add_computed_property_value(
+                                  keyframe, index, style, property, &global_style_data.shared_lock);
                               index += 1;
                           }
                       }
diff --git a/ports/geckolib/lib.rs b/ports/geckolib/lib.rs
index 0bdbaa12f24..a7dd0561299 100644
--- a/ports/geckolib/lib.rs
+++ b/ports/geckolib/lib.rs
@@ -10,9 +10,7 @@ extern crate env_logger;
 #[macro_use] extern crate lazy_static;
 extern crate libc;
 #[macro_use] extern crate log;
-extern crate num_cpus;
 extern crate parking_lot;
-extern crate rayon;
 extern crate selectors;
 extern crate servo_url;
 #[macro_use] extern crate style;
diff --git a/ports/geckolib/stylesheet_loader.rs b/ports/geckolib/stylesheet_loader.rs
index 2e81de1a57e..5e226ee54c9 100644
--- a/ports/geckolib/stylesheet_loader.rs
+++ b/ports/geckolib/stylesheet_loader.rs
@@ -3,13 +3,13 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use std::sync::Arc;
+use style::gecko::global_style_data::GLOBAL_STYLE_DATA;
 use style::gecko_bindings::bindings::Gecko_LoadStyleSheet;
 use style::gecko_bindings::structs::{Loader, ServoStyleSheet};
 use style::gecko_bindings::sugar::ownership::HasArcFFI;
 use style::shared_lock::Locked;
 use style::stylesheets::{ImportRule, StylesheetLoader as StyleStylesheetLoader};
 use style_traits::ToCss;
-use super::glue::GLOBAL_STYLE_DATA;
 
 pub struct StylesheetLoader(*mut Loader, *mut ServoStyleSheet);
 
diff --git a/tests/unit/style/keyframes.rs b/tests/unit/style/keyframes.rs
index a916f18da01..9fe2f0d3f39 100644
--- a/tests/unit/style/keyframes.rs
+++ b/tests/unit/style/keyframes.rs
@@ -2,7 +2,6 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use parking_lot::RwLock;
 use std::sync::Arc;
 use style::keyframes::{Keyframe, KeyframesAnimation, KeyframePercentage,  KeyframeSelector};
 use style::keyframes::{KeyframesStep, KeyframesStepValue};
@@ -30,7 +29,7 @@ fn test_no_property_in_keyframe() {
     let keyframes = vec![
         Arc::new(shared_lock.wrap(Keyframe {
             selector: KeyframeSelector::new_for_unit_testing(vec![KeyframePercentage::new(1.)]),
-            block: Arc::new(RwLock::new(PropertyDeclarationBlock::new()))
+            block: Arc::new(shared_lock.wrap(PropertyDeclarationBlock::new()))
         })),
     ];
     let animation = KeyframesAnimation::from_keyframes(&keyframes, &shared_lock.read());
@@ -46,14 +45,14 @@ fn test_no_property_in_keyframe() {
 fn test_missing_property_in_initial_keyframe() {
     let shared_lock = SharedRwLock::new();
     let declarations_on_initial_keyframe =
-        Arc::new(RwLock::new(PropertyDeclarationBlock::with_one(
+        Arc::new(shared_lock.wrap(PropertyDeclarationBlock::with_one(
             PropertyDeclaration::Width(
                 LengthOrPercentageOrAuto::Length(NoCalcLength::from_px(20f32))),
             Importance::Normal
         )));
 
     let declarations_on_final_keyframe =
-        Arc::new(RwLock::new({
+        Arc::new(shared_lock.wrap({
             let mut block = PropertyDeclarationBlock::new();
             block.push(
                 PropertyDeclaration::Width(
@@ -103,7 +102,7 @@ fn test_missing_property_in_initial_keyframe() {
 fn test_missing_property_in_final_keyframe() {
     let shared_lock = SharedRwLock::new();
     let declarations_on_initial_keyframe =
-        Arc::new(RwLock::new({
+        Arc::new(shared_lock.wrap({
             let mut block = PropertyDeclarationBlock::new();
             block.push(
                 PropertyDeclaration::Width(
@@ -119,7 +118,7 @@ fn test_missing_property_in_final_keyframe() {
         }));
 
     let declarations_on_final_keyframe =
-        Arc::new(RwLock::new(PropertyDeclarationBlock::with_one(
+        Arc::new(shared_lock.wrap(PropertyDeclarationBlock::with_one(
             PropertyDeclaration::Height(
                 LengthOrPercentageOrAuto::Length(NoCalcLength::from_px(20f32))),
             Importance::Normal,
@@ -160,7 +159,7 @@ fn test_missing_property_in_final_keyframe() {
 fn test_missing_keyframe_in_both_of_initial_and_final_keyframe() {
     let shared_lock = SharedRwLock::new();
     let declarations =
-        Arc::new(RwLock::new({
+        Arc::new(shared_lock.wrap({
             let mut block = PropertyDeclarationBlock::new();
             block.push(
                 PropertyDeclaration::Width(
@@ -178,7 +177,7 @@ fn test_missing_keyframe_in_both_of_initial_and_final_keyframe() {
     let keyframes = vec![
         Arc::new(shared_lock.wrap(Keyframe {
             selector: KeyframeSelector::new_for_unit_testing(vec![KeyframePercentage::new(0.)]),
-            block: Arc::new(RwLock::new(PropertyDeclarationBlock::new()))
+            block: Arc::new(shared_lock.wrap(PropertyDeclarationBlock::new()))
         })),
         Arc::new(shared_lock.wrap(Keyframe {
             selector: KeyframeSelector::new_for_unit_testing(vec![KeyframePercentage::new(0.5)]),
@@ -191,7 +190,7 @@ fn test_missing_keyframe_in_both_of_initial_and_final_keyframe() {
             KeyframesStep {
                 start_percentage: KeyframePercentage(0.),
                 value: KeyframesStepValue::Declarations {
-                    block: Arc::new(RwLock::new(
+                    block: Arc::new(shared_lock.wrap(
                         // XXX: Should we use ComputedValues in this case?
                         PropertyDeclarationBlock::new()
                     ))
diff --git a/tests/unit/style/rule_tree/bench.rs b/tests/unit/style/rule_tree/bench.rs
index aeac93912aa..4d4012f16c1 100644
--- a/tests/unit/style/rule_tree/bench.rs
+++ b/tests/unit/style/rule_tree/bench.rs
@@ -3,7 +3,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use cssparser::{Parser, SourcePosition};
-use parking_lot::RwLock;
 use rayon;
 use servo_url::ServoUrl;
 use std::sync::Arc;
@@ -65,9 +64,11 @@ fn test_insertion(rule_tree: &RuleTree, rules: Vec<(StyleSource, CascadeLevel)>)
     rule_tree.insert_ordered_rules(rules.into_iter())
 }
 
-fn test_insertion_style_attribute(rule_tree: &RuleTree, rules: &[(StyleSource, CascadeLevel)]) -> StrongRuleNode {
+fn test_insertion_style_attribute(rule_tree: &RuleTree, rules: &[(StyleSource, CascadeLevel)],
+                                  shared_lock: &SharedRwLock)
+                                  -> StrongRuleNode {
     let mut rules = rules.to_vec();
-    rules.push((StyleSource::Declarations(Arc::new(RwLock::new(PropertyDeclarationBlock::with_one(
+    rules.push((StyleSource::Declarations(Arc::new(shared_lock.wrap(PropertyDeclarationBlock::with_one(
         PropertyDeclaration::Display(
             longhands::display::SpecifiedValue::block),
         Importance::Normal
@@ -121,11 +122,12 @@ fn bench_expensive_insertion(b: &mut Bencher) {
          .bar { height: 500px; } \
          .baz { display: block; }");
 
+    let shared_lock = SharedRwLock::new();
     b.iter(|| {
         let _gc = AutoGCRuleTree::new(&r);
 
         for _ in 0..(4000 + 400) {
-            test::black_box(test_insertion_style_attribute(&r, &rules_matched));
+            test::black_box(test_insertion_style_attribute(&r, &rules_matched, &shared_lock));
         }
     });
 }
@@ -170,6 +172,7 @@ fn bench_expensive_insersion_parallel(b: &mut Bencher) {
          .bar { height: 500px; } \
          .baz { display: block; }");
 
+    let shared_lock = SharedRwLock::new();
     b.iter(|| {
         let _gc = AutoGCRuleTree::new(&r);
 
@@ -178,12 +181,14 @@ fn bench_expensive_insersion_parallel(b: &mut Bencher) {
                 s.spawn(|s| {
                     for _ in 0..1000 {
                         test::black_box(test_insertion_style_attribute(&r,
-                                                                       &rules_matched));
+                                                                       &rules_matched,
+                                                                       &shared_lock));
                     }
                     s.spawn(|_| {
                         for _ in 0..100 {
                             test::black_box(test_insertion_style_attribute(&r,
-                                                                           &rules_matched));
+                                                                           &rules_matched,
+                                                                           &shared_lock));
                         }
                     })
                 })
diff --git a/tests/unit/style/stylesheets.rs b/tests/unit/style/stylesheets.rs
index 2bcb9b58a77..fa6a26963f8 100644
--- a/tests/unit/style/stylesheets.rs
+++ b/tests/unit/style/stylesheets.rs
@@ -109,7 +109,7 @@ fn test_parse_stylesheet() {
                         specificity: (0 << 20) + (1 << 10) + (1 << 0),
                     },
                 ]),
-                block: Arc::new(RwLock::new(block_from(vec![
+                block: Arc::new(stylesheet.shared_lock.wrap(block_from(vec![
                     (PropertyDeclaration::Display(longhands::display::SpecifiedValue::none),
                      Importance::Important),
                     (PropertyDeclaration::Custom(Atom::from("a"),
@@ -154,7 +154,7 @@ fn test_parse_stylesheet() {
                         specificity: (0 << 20) + (0 << 10) + (1 << 0),
                     },
                 ]),
-                block: Arc::new(RwLock::new(block_from(vec![
+                block: Arc::new(stylesheet.shared_lock.wrap(block_from(vec![
                     (PropertyDeclaration::Display(longhands::display::SpecifiedValue::block),
                      Importance::Normal),
                 ]))),
@@ -185,7 +185,7 @@ fn test_parse_stylesheet() {
                         specificity: (1 << 20) + (1 << 10) + (0 << 0),
                     },
                 ]),
-                block: Arc::new(RwLock::new(block_from(vec![
+                block: Arc::new(stylesheet.shared_lock.wrap(block_from(vec![
                     (PropertyDeclaration::BackgroundColor(
                         longhands::background_color::SpecifiedValue {
                             authored: Some("blue".to_owned().into_boxed_str()),
@@ -241,7 +241,7 @@ fn test_parse_stylesheet() {
                     Arc::new(stylesheet.shared_lock.wrap(Keyframe {
                         selector: KeyframeSelector::new_for_unit_testing(
                                       vec![KeyframePercentage::new(0.)]),
-                        block: Arc::new(RwLock::new(block_from(vec![
+                        block: Arc::new(stylesheet.shared_lock.wrap(block_from(vec![
                             (PropertyDeclaration::Width(
                                 LengthOrPercentageOrAuto::Percentage(Percentage(0.))),
                              Importance::Normal),
@@ -250,7 +250,7 @@ fn test_parse_stylesheet() {
                     Arc::new(stylesheet.shared_lock.wrap(Keyframe {
                         selector: KeyframeSelector::new_for_unit_testing(
                                       vec![KeyframePercentage::new(1.)]),
-                        block: Arc::new(RwLock::new(block_from(vec![
+                        block: Arc::new(stylesheet.shared_lock.wrap(block_from(vec![
                             (PropertyDeclaration::Width(
                                 LengthOrPercentageOrAuto::Percentage(Percentage(1.))),
                              Importance::Normal),
diff --git a/tests/unit/style/stylist.rs b/tests/unit/style/stylist.rs
index 34a7feff965..8f559703cbe 100644
--- a/tests/unit/style/stylist.rs
+++ b/tests/unit/style/stylist.rs
@@ -3,7 +3,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use html5ever_atoms::LocalName;
-use parking_lot::RwLock;
 use selectors::parser::LocalName as LocalNameSelector;
 use servo_atoms::Atom;
 use std::sync::Arc;
@@ -25,7 +24,7 @@ fn get_mock_rules(css_selectors: &[&str]) -> (Vec<Vec<Rule>>, SharedRwLock) {
 
         let locked = Arc::new(shared_lock.wrap(StyleRule {
             selectors: selectors,
-            block: Arc::new(RwLock::new(PropertyDeclarationBlock::with_one(
+            block: Arc::new(shared_lock.wrap(PropertyDeclarationBlock::with_one(
                 PropertyDeclaration::Display(
                     longhands::display::SpecifiedValue::block),
                 Importance::Normal

From 1e380137831eaf94a1f602c9d8dfae08f10893fa Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Sat, 18 Mar 2017 13:49:04 +0100
Subject: [PATCH 13/17] Refactor StylesheetLoader so impls do not need to
 acquire a shared lock.

This fixes a deadlock:
https://github.com/servo/servo/pull/16014#issuecomment-287527067
---
 components/script/dom/htmllinkelement.rs |  3 +-
 components/script/stylesheet_loader.rs   | 45 ++++++++---------
 components/style/stylesheets.rs          | 61 ++++++++++++++++--------
 ports/geckolib/stylesheet_loader.rs      | 34 ++++++++-----
 4 files changed, 84 insertions(+), 59 deletions(-)

diff --git a/components/script/dom/htmllinkelement.rs b/components/script/dom/htmllinkelement.rs
index b4f90b89b85..d29a94a11f0 100644
--- a/components/script/dom/htmllinkelement.rs
+++ b/components/script/dom/htmllinkelement.rs
@@ -291,9 +291,8 @@ impl HTMLLinkElement {
         // doesn't match.
         let loader = StylesheetLoader::for_element(self.upcast());
         loader.load(StylesheetContextSource::LinkElement {
-            url: url,
             media: Some(media),
-        }, cors_setting, integrity_metadata.to_owned());
+        }, url, cors_setting, integrity_metadata.to_owned());
     }
 
     fn handle_favicon_url(&self, rel: &str, href: &str, sizes: &Option<String>) {
diff --git a/components/script/stylesheet_loader.rs b/components/script/stylesheet_loader.rs
index db21ee795fd..7f544e42d08 100644
--- a/components/script/stylesheet_loader.rs
+++ b/components/script/stylesheet_loader.rs
@@ -54,32 +54,16 @@ pub trait StylesheetOwner {
 
 pub enum StylesheetContextSource {
     // NB: `media` is just an option so we avoid cloning it.
-    LinkElement { media: Option<MediaList>, url: ServoUrl },
+    LinkElement { media: Option<MediaList>, },
     Import(Arc<StyleLocked<ImportRule>>),
 }
 
-impl StylesheetContextSource {
-    fn url(&self, document: &Document) -> ServoUrl {
-        match *self {
-            StylesheetContextSource::LinkElement { ref url, .. } => url.clone(),
-            StylesheetContextSource::Import(ref import) => {
-                let guard = document.style_shared_lock().read();
-                let import = import.read_with(&guard);
-                // Look at the parser in style::stylesheets, where we don't
-                // trigger a load if the url is invalid.
-                import.url.url()
-                    .expect("Invalid urls shouldn't enter the loader")
-                    .clone()
-            }
-        }
-    }
-}
-
 /// The context required for asynchronously loading an external stylesheet.
 pub struct StylesheetContext {
     /// The element that initiated the request.
     elem: Trusted<HTMLElement>,
     source: StylesheetContextSource,
+    url: ServoUrl,
     metadata: Option<Metadata>,
     /// The response body received to date.
     data: Vec<u8>,
@@ -146,7 +130,7 @@ impl FetchResponseListener for StylesheetContext {
 
             let loader = StylesheetLoader::for_element(&elem);
             match self.source {
-                StylesheetContextSource::LinkElement { ref mut media, .. } => {
+                StylesheetContextSource::LinkElement { ref mut media } => {
                     let link = elem.downcast::<HTMLLinkElement>().unwrap();
                     // We must first check whether the generations of the context and the element match up,
                     // else we risk applying the wrong stylesheet when responses come out-of-order.
@@ -209,8 +193,7 @@ impl FetchResponseListener for StylesheetContext {
             document.decrement_script_blocking_stylesheet_count();
         }
 
-        let url = self.source.url(&document);
-        document.finish_load(LoadType::Stylesheet(url));
+        document.finish_load(LoadType::Stylesheet(self.url.clone()));
 
         if let Some(any_failed) = owner.load_finished(successful) {
             let event = if any_failed { atom!("error") } else { atom!("load") };
@@ -232,15 +215,16 @@ impl<'a> StylesheetLoader<'a> {
 }
 
 impl<'a> StylesheetLoader<'a> {
-    pub fn load(&self, source: StylesheetContextSource, cors_setting: Option<CorsSettings>,
+    pub fn load(&self, source: StylesheetContextSource, url: ServoUrl,
+                cors_setting: Option<CorsSettings>,
                 integrity_metadata: String) {
         let document = document_from_node(self.elem);
-        let url = source.url(&document);
         let gen = self.elem.downcast::<HTMLLinkElement>()
                            .map(HTMLLinkElement::get_request_generation_id);
         let context = Arc::new(Mutex::new(StylesheetContext {
             elem: Trusted::new(&*self.elem),
             source: source,
+            url: url.clone(),
             metadata: None,
             data: vec![],
             document: Trusted::new(&*document),
@@ -297,9 +281,20 @@ impl<'a> StylesheetLoader<'a> {
 }
 
 impl<'a> StyleStylesheetLoader for StylesheetLoader<'a> {
-    fn request_stylesheet(&self, import: &Arc<StyleLocked<ImportRule>>) {
+    fn request_stylesheet(
+        &self,
+        media: MediaList,
+        make_import: &mut FnMut(MediaList) -> ImportRule,
+        make_arc: &mut FnMut(ImportRule) -> Arc<StyleLocked<ImportRule>>,
+    ) -> Arc<StyleLocked<ImportRule>> {
+        let import = make_import(media);
+        let url = import.url.url().expect("Invalid urls shouldn't enter the loader").clone();
+        let arc = make_arc(import);
+
         //TODO (mrnayak) : Whether we should use the original loader's CORS setting?
         //Fix this when spec has more details.
-        self.load(StylesheetContextSource::Import(import.clone()), None, "".to_owned())
+        self.load(StylesheetContextSource::Import(arc.clone()), url, None, "".to_owned());
+
+        arc
     }
 }
diff --git a/components/style/stylesheets.rs b/components/style/stylesheets.rs
index 95104a4df60..3d572536d7d 100644
--- a/components/style/stylesheets.rs
+++ b/components/style/stylesheets.rs
@@ -743,9 +743,31 @@ pub trait StylesheetLoader {
     ///
     /// The called code is responsible to update the `stylesheet` rules field
     /// when the sheet is done loading.
-    fn request_stylesheet(&self, import: &Arc<Locked<ImportRule>>);
+    ///
+    /// The convoluted signature allows impls to look at MediaList and ImportRule
+    /// before they’re locked, while keeping the trait object-safe.
+    fn request_stylesheet(
+        &self,
+        media: MediaList,
+        make_import: &mut FnMut(MediaList) -> ImportRule,
+        make_arc: &mut FnMut(ImportRule) -> Arc<Locked<ImportRule>>,
+    ) -> Arc<Locked<ImportRule>>;
 }
 
+struct NoOpLoader;
+
+impl StylesheetLoader for NoOpLoader {
+    fn request_stylesheet(
+        &self,
+        media: MediaList,
+        make_import: &mut FnMut(MediaList) -> ImportRule,
+        make_arc: &mut FnMut(ImportRule) -> Arc<Locked<ImportRule>>,
+    ) -> Arc<Locked<ImportRule>> {
+        make_arc(make_import(media))
+    }
+}
+
+
 struct TopLevelRuleParser<'a> {
     stylesheet_origin: Origin,
     namespaces: &'a mut Namespaces,
@@ -801,22 +823,26 @@ impl<'a> AtRuleParser for TopLevelRuleParser<'a> {
             "import" => {
                 if self.state.get() <= State::Imports {
                     self.state.set(State::Imports);
-                    let url = try!(input.expect_url_or_string());
-                    let url =
-                        try!(SpecifiedUrl::parse_from_string(url,
-                                                             &self.context));
+                    let url_string = input.expect_url_or_string()?;
+                    let specified_url = SpecifiedUrl::parse_from_string(url_string, &self.context)?;
 
-                    let media =
-                        Arc::new(self.shared_lock.wrap(parse_media_query_list(input)));
+                    let media = parse_media_query_list(input);
 
-                    let is_valid_url = url.url().is_some();
+                    let noop_loader = NoOpLoader;
+                    let is_valid_url = specified_url.url().is_some();
+                    let loader = if is_valid_url {
+                        self.loader.expect("Expected a stylesheet loader for @import")
+                    } else {
+                        &noop_loader
+                    };
 
-                    let import_rule = Arc::new(self.shared_lock.wrap(
+                    let mut specified_url = Some(specified_url);
+                    let arc = loader.request_stylesheet(media, &mut |media| {
                         ImportRule {
-                            url: url,
+                            url: specified_url.take().unwrap(),
                             stylesheet: Arc::new(Stylesheet {
                                 rules: CssRules::new(Vec::new(), self.shared_lock),
-                                media: media,
+                                media: Arc::new(self.shared_lock.wrap(media)),
                                 shared_lock: self.shared_lock.clone(),
                                 origin: self.context.stylesheet_origin,
                                 base_url: self.context.base_url.clone(),
@@ -825,15 +851,10 @@ impl<'a> AtRuleParser for TopLevelRuleParser<'a> {
                                 disabled: AtomicBool::new(false),
                             })
                         }
-                    ));
-
-                    if is_valid_url {
-                        let loader = self.loader
-                            .expect("Expected a stylesheet loader for @import");
-                        loader.request_stylesheet(&import_rule);
-                    }
-
-                    return Ok(AtRuleType::WithoutBlock(CssRule::Import(import_rule)))
+                    }, &mut |import_rule| {
+                        Arc::new(self.shared_lock.wrap(import_rule))
+                    });
+                    return Ok(AtRuleType::WithoutBlock(CssRule::Import(arc)))
                 } else {
                     self.state.set(State::Invalid);
                     return Err(())  // "@import must be before any rule but @charset"
diff --git a/ports/geckolib/stylesheet_loader.rs b/ports/geckolib/stylesheet_loader.rs
index 5e226ee54c9..d904f1b9870 100644
--- a/ports/geckolib/stylesheet_loader.rs
+++ b/ports/geckolib/stylesheet_loader.rs
@@ -3,10 +3,10 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use std::sync::Arc;
-use style::gecko::global_style_data::GLOBAL_STYLE_DATA;
 use style::gecko_bindings::bindings::Gecko_LoadStyleSheet;
 use style::gecko_bindings::structs::{Loader, ServoStyleSheet};
 use style::gecko_bindings::sugar::ownership::HasArcFFI;
+use style::media_queries::MediaList;
 use style::shared_lock::Locked;
 use style::stylesheets::{ImportRule, StylesheetLoader as StyleStylesheetLoader};
 use style_traits::ToCss;
@@ -20,13 +20,12 @@ impl StylesheetLoader {
 }
 
 impl StyleStylesheetLoader for StylesheetLoader {
-    fn request_stylesheet(&self, import_rule: &Arc<Locked<ImportRule>>) {
-        let global_style_data = &*GLOBAL_STYLE_DATA;
-        let guard = global_style_data.shared_lock.read();
-        let import = import_rule.read_with(&guard);
-        let (spec_bytes, spec_len) = import.url.as_slice_components()
-            .expect("Import only loads valid URLs");
-
+    fn request_stylesheet(
+        &self,
+        media: MediaList,
+        make_import: &mut FnMut(MediaList) -> ImportRule,
+        make_arc: &mut FnMut(ImportRule) -> Arc<Locked<ImportRule>>,
+    ) -> Arc<Locked<ImportRule>> {
         // TODO(emilio): We probably want to share media representation with
         // Gecko in Stylo.
         //
@@ -35,16 +34,27 @@ impl StyleStylesheetLoader for StylesheetLoader {
         // evaluate them on the main thread.
         //
         // Meanwhile, this works.
-        let media = import.stylesheet.media.read_with(&guard).to_css_string();
+        let media_string = media.to_css_string();
 
+        let import = make_import(media);
+
+        // After we get this raw pointer ImportRule will be moved into a lock and Arc
+        // and so the Arc<Url> pointer inside will also move,
+        // but the Url it points to or the allocating backing the String inside that Url won’t,
+        // so this raw pointer will still be valid.
+        let (spec_bytes, spec_len): (*const u8, usize) = import.url.as_slice_components()
+            .expect("Import only loads valid URLs");
+
+        let arc = make_arc(import);
         unsafe {
             Gecko_LoadStyleSheet(self.0,
                                  self.1,
-                                 HasArcFFI::arc_as_borrowed(import_rule),
+                                 HasArcFFI::arc_as_borrowed(&arc),
                                  spec_bytes,
                                  spec_len as u32,
-                                 media.as_bytes().as_ptr(),
-                                 media.len() as u32);
+                                 media_string.as_bytes().as_ptr(),
+                                 media_string.len() as u32);
         }
+        arc
     }
 }

From cc046300f0390eadfcff65dcc6d8cea5bed9513e Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Sat, 18 Mar 2017 14:00:01 +0100
Subject: [PATCH 14/17] Remove some indirection.

---
 components/script/stylesheet_loader.rs | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/components/script/stylesheet_loader.rs b/components/script/stylesheet_loader.rs
index 7f544e42d08..fc838319695 100644
--- a/components/script/stylesheet_loader.rs
+++ b/components/script/stylesheet_loader.rs
@@ -55,7 +55,7 @@ pub trait StylesheetOwner {
 pub enum StylesheetContextSource {
     // NB: `media` is just an option so we avoid cloning it.
     LinkElement { media: Option<MediaList>, },
-    Import(Arc<StyleLocked<ImportRule>>),
+    Import(Arc<Stylesheet>),
 }
 
 /// The context required for asynchronously loading an external stylesheet.
@@ -158,16 +158,9 @@ impl FetchResponseListener for StylesheetContext {
                         win.layout_chan().send(Msg::AddStylesheet(sheet)).unwrap();
                     }
                 }
-                StylesheetContextSource::Import(ref import) => {
+                StylesheetContextSource::Import(ref stylesheet) => {
                     let mut guard = document.style_shared_lock().write();
 
-                    // Clone an Arc because we can’t borrow `guard` twice at the same time.
-
-                    // FIXME(SimonSapin): allow access to multiple objects with one write guard?
-                    // Would need a set of usize pointer addresses or something,
-                    // the same object is not accessed more than once.
-                    let stylesheet = Arc::clone(&import.write_with(&mut guard).stylesheet);
-
                     Stylesheet::update_from_bytes(&stylesheet,
                                                   &data,
                                                   protocol_encoding_label,
@@ -289,12 +282,12 @@ impl<'a> StyleStylesheetLoader for StylesheetLoader<'a> {
     ) -> Arc<StyleLocked<ImportRule>> {
         let import = make_import(media);
         let url = import.url.url().expect("Invalid urls shouldn't enter the loader").clone();
-        let arc = make_arc(import);
 
         //TODO (mrnayak) : Whether we should use the original loader's CORS setting?
         //Fix this when spec has more details.
-        self.load(StylesheetContextSource::Import(arc.clone()), url, None, "".to_owned());
+        let source = StylesheetContextSource::Import(import.stylesheet.clone());
+        self.load(source, url, None, "".to_owned());
 
-        arc
+        make_arc(import)
     }
 }

From d9491187dc7509b4114bfb3d606986fac28e5ff8 Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Sat, 18 Mar 2017 14:25:25 +0100
Subject: [PATCH 15/17] Parse stylesheets without acquiring a shared lock.

---
 components/script/stylesheet_loader.rs |  3 --
 components/style/encoding_support.rs   |  4 +-
 components/style/stylesheets.rs        | 70 +++++++++++++++-----------
 ports/geckolib/glue.rs                 |  7 +--
 4 files changed, 42 insertions(+), 42 deletions(-)

diff --git a/components/script/stylesheet_loader.rs b/components/script/stylesheet_loader.rs
index fc838319695..4c2f06322a4 100644
--- a/components/script/stylesheet_loader.rs
+++ b/components/script/stylesheet_loader.rs
@@ -159,13 +159,10 @@ impl FetchResponseListener for StylesheetContext {
                     }
                 }
                 StylesheetContextSource::Import(ref stylesheet) => {
-                    let mut guard = document.style_shared_lock().write();
-
                     Stylesheet::update_from_bytes(&stylesheet,
                                                   &data,
                                                   protocol_encoding_label,
                                                   Some(environment_encoding),
-                                                  &mut guard,
                                                   Some(&loader),
                                                   win.css_error_reporter(),
                                                   ParserContextExtraData::default());
diff --git a/components/style/encoding_support.rs b/components/style/encoding_support.rs
index e485dc13cf0..141291c896e 100644
--- a/components/style/encoding_support.rs
+++ b/components/style/encoding_support.rs
@@ -12,7 +12,7 @@ use media_queries::MediaList;
 use parser::ParserContextExtraData;
 use self::encoding::{EncodingRef, DecoderTrap};
 use servo_url::ServoUrl;
-use shared_lock::{SharedRwLock, SharedRwLockWriteGuard};
+use shared_lock::SharedRwLock;
 use std::str;
 use stylesheets::{Stylesheet, StylesheetLoader, Origin};
 
@@ -78,7 +78,6 @@ impl Stylesheet {
                              bytes: &[u8],
                              protocol_encoding_label: Option<&str>,
                              environment_encoding: Option<EncodingRef>,
-                             guard: &mut SharedRwLockWriteGuard,
                              stylesheet_loader: Option<&StylesheetLoader>,
                              error_reporter: &ParseErrorReporter,
                              extra_data: ParserContextExtraData) {
@@ -86,7 +85,6 @@ impl Stylesheet {
             bytes, protocol_encoding_label, environment_encoding);
         Self::update_from_str(existing,
                               &string,
-                              guard,
                               stylesheet_loader,
                               error_reporter,
                               extra_data)
diff --git a/components/style/stylesheets.rs b/components/style/stylesheets.rs
index 3d572536d7d..202c31f7416 100644
--- a/components/style/stylesheets.rs
+++ b/components/style/stylesheets.rs
@@ -21,8 +21,7 @@ use selector_parser::{SelectorImpl, SelectorParser};
 use selectors::parser::SelectorList;
 use servo_config::prefs::PREFS;
 use servo_url::ServoUrl;
-use shared_lock::{SharedRwLock, Locked, ToCssWithGuard};
-use shared_lock::{SharedRwLockReadGuard, SharedRwLockWriteGuard};
+use shared_lock::{SharedRwLock, Locked, ToCssWithGuard, SharedRwLockReadGuard};
 use std::cell::Cell;
 use std::fmt;
 use std::sync::Arc;
@@ -556,23 +555,42 @@ impl Stylesheet {
     /// Updates an empty stylesheet from a given string of text.
     pub fn update_from_str(existing: &Stylesheet,
                            css: &str,
-                           guard: &mut SharedRwLockWriteGuard,
                            stylesheet_loader: Option<&StylesheetLoader>,
                            error_reporter: &ParseErrorReporter,
                            extra_data: ParserContextExtraData) {
-        let mut rules = existing.rules.write_with(guard);
-        let mut namespaces = existing.namespaces.write();
+        let mut namespaces = Namespaces::default();
+        let (rules, dirty_on_viewport_size_change) = Stylesheet::parse_rules(
+            css, &existing.base_url, existing.origin, &mut namespaces, &existing.shared_lock,
+            stylesheet_loader, error_reporter, extra_data,
+        );
 
-        assert!(rules.is_empty());
+        *existing.namespaces.write() = namespaces;
+        existing.dirty_on_viewport_size_change
+            .store(dirty_on_viewport_size_change, Ordering::Release);
 
+        // Acquire the lock *after* parsing, to minimize the exclusive section.
+        let mut guard = existing.shared_lock.write();
+        *existing.rules.write_with(&mut guard) = CssRules(rules);
+    }
+
+    fn parse_rules(css: &str,
+                   base_url: &ServoUrl,
+                   origin: Origin,
+                   namespaces: &mut Namespaces,
+                   shared_lock: &SharedRwLock,
+                   stylesheet_loader: Option<&StylesheetLoader>,
+                   error_reporter: &ParseErrorReporter,
+                   extra_data: ParserContextExtraData)
+                   -> (Vec<CssRule>, bool) {
+        let mut rules = Vec::new();
         let mut input = Parser::new(css);
         let rule_parser = TopLevelRuleParser {
-            stylesheet_origin: existing.origin,
-            namespaces: &mut namespaces,
-            shared_lock: &existing.shared_lock,
+            stylesheet_origin: origin,
+            namespaces: namespaces,
+            shared_lock: shared_lock,
             loader: stylesheet_loader,
-            context: ParserContext::new_with_extra_data(existing.origin,
-                                                        &existing.base_url,
+            context: ParserContext::new_with_extra_data(origin,
+                                                        base_url,
                                                         error_reporter,
                                                         extra_data),
             state: Cell::new(State::Start),
@@ -584,7 +602,7 @@ impl Stylesheet {
             let mut iter = RuleListParser::new_for_stylesheet(&mut input, rule_parser);
             while let Some(result) = iter.next() {
                 match result {
-                    Ok(rule) => rules.0.push(rule),
+                    Ok(rule) => rules.push(rule),
                     Err(range) => {
                         let pos = range.start;
                         let message = format!("Invalid rule: '{}'", iter.input.slice(range));
@@ -594,8 +612,7 @@ impl Stylesheet {
             }
         }
 
-        existing.dirty_on_viewport_size_change
-            .store(input.seen_viewport_percentages(), Ordering::Release);
+        (rules, input.seen_viewport_percentages())
     }
 
     /// Creates an empty stylesheet and parses it with a given base url, origin
@@ -611,28 +628,21 @@ impl Stylesheet {
                     stylesheet_loader: Option<&StylesheetLoader>,
                     error_reporter: &ParseErrorReporter,
                     extra_data: ParserContextExtraData) -> Stylesheet {
-        let s = Stylesheet {
+        let mut namespaces = Namespaces::default();
+        let (rules, dirty_on_viewport_size_change) = Stylesheet::parse_rules(
+            css, &base_url, origin, &mut namespaces, &shared_lock,
+            stylesheet_loader, error_reporter, extra_data,
+        );
+        Stylesheet {
             origin: origin,
             base_url: base_url,
-            namespaces: RwLock::new(Namespaces::default()),
-            rules: CssRules::new(Vec::new(), &shared_lock),
+            namespaces: RwLock::new(namespaces),
+            rules: CssRules::new(rules, &shared_lock),
             media: Arc::new(shared_lock.wrap(media)),
             shared_lock: shared_lock,
-            dirty_on_viewport_size_change: AtomicBool::new(false),
+            dirty_on_viewport_size_change: AtomicBool::new(dirty_on_viewport_size_change),
             disabled: AtomicBool::new(false),
-        };
-
-        {
-            let mut guard = s.shared_lock.write();
-            Self::update_from_str(&s,
-                                  css,
-                                  &mut guard,
-                                  stylesheet_loader,
-                                  error_reporter,
-                                  extra_data);
         }
-
-        s
     }
 
     /// Whether this stylesheet can be dirty on viewport size change.
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index f39e4a903cc..82cbd7aef74 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -362,8 +362,6 @@ pub extern "C" fn Servo_StyleSheet_ClearAndUpdate(stylesheet: RawServoStyleSheet
                                                   referrer: *mut ThreadSafeURIHolder,
                                                   principal: *mut ThreadSafePrincipalHolder)
 {
-    let global_style_data = &*GLOBAL_STYLE_DATA;
-    let mut guard = global_style_data.shared_lock.write();
     let input = unsafe { data.as_ref().unwrap().as_str_unchecked() };
     let extra_data = unsafe { ParserContextExtraData {
         base: Some(GeckoArcURI::new(base)),
@@ -384,10 +382,7 @@ pub extern "C" fn Servo_StyleSheet_ClearAndUpdate(stylesheet: RawServoStyleSheet
     };
 
     let sheet = Stylesheet::as_arc(&stylesheet);
-    sheet.rules.write_with(&mut guard).0.clear();
-
-    Stylesheet::update_from_str(&sheet, input, &mut guard, loader,
-                                &StdoutErrorReporter, extra_data);
+    Stylesheet::update_from_str(&sheet, input, loader, &StdoutErrorReporter, extra_data);
 }
 
 #[no_mangle]

From 2952ccfae2e4883efc4886988dcf17d07d89f66c Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Sat, 18 Mar 2017 15:41:50 +0100
Subject: [PATCH 16/17] Fix another deadlock

---
 components/script/dom/cssrulelist.rs | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/components/script/dom/cssrulelist.rs b/components/script/dom/cssrulelist.rs
index bc77361b5ae..1f1573a05d5 100644
--- a/components/script/dom/cssrulelist.rs
+++ b/components/script/dom/cssrulelist.rs
@@ -90,9 +90,12 @@ impl CSSRuleList {
         let index = idx as usize;
 
         let parent_stylesheet = self.parent_stylesheet.style_stylesheet();
-        let mut guard = parent_stylesheet.shared_lock.write();
-        let new_rule = css_rules.write_with(&mut guard)
-            .insert_rule(rule, parent_stylesheet, index, nested)?;
+        let new_rule = {
+            let mut guard = parent_stylesheet.shared_lock.write();
+            css_rules.write_with(&mut guard).insert_rule(rule, parent_stylesheet, index, nested)?
+            // Drop `guard` here,
+            // CSSRule::new_specific re-acquires the lock for @support and @media.
+        };
 
         let parent_stylesheet = &*self.parent_stylesheet;
         let dom_rule = CSSRule::new_specific(&window, parent_stylesheet, new_rule);

From d5074136e303544d108dc5615f96e92b854752ee Mon Sep 17 00:00:00 2001
From: Simon Sapin <simon.sapin@exyr.org>
Date: Sat, 18 Mar 2017 20:12:23 +0100
Subject: [PATCH 17/17] Rename ReadGuards to StylesheetGuards

---
 components/layout_thread/lib.rs                |  8 ++++----
 components/style/context.rs                    |  4 ++--
 components/style/gecko/data.rs                 |  4 ++--
 components/style/properties/properties.mako.rs |  4 ++--
 components/style/rule_tree/mod.rs              | 12 ++++++------
 components/style/shared_lock.rs                |  6 +++---
 components/style/stylist.rs                    | 12 ++++++------
 ports/geckolib/glue.rs                         |  8 ++++----
 8 files changed, 29 insertions(+), 29 deletions(-)

diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index 32708911484..1ebee7b5ead 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -116,7 +116,7 @@ use style::media_queries::{Device, MediaType};
 use style::parser::ParserContextExtraData;
 use style::servo::AUTHOR_SHARED_LOCK;
 use style::servo::restyle_damage::{REFLOW, REFLOW_OUT_OF_FLOW, REPAINT, REPOSITION, STORE_OVERFLOW};
-use style::shared_lock::{SharedRwLock, SharedRwLockReadGuard, ReadGuards};
+use style::shared_lock::{SharedRwLock, SharedRwLockReadGuard, StylesheetGuards};
 use style::stylesheets::{Origin, Stylesheet, UserAgentStylesheets};
 use style::stylist::Stylist;
 use style::thread_state;
@@ -500,7 +500,7 @@ impl LayoutThread {
 
     // Create a layout context for use in building display lists, hit testing, &c.
     fn build_layout_context<'a>(&self,
-                                guards: ReadGuards<'a>,
+                                guards: StylesheetGuards<'a>,
                                 rw_data: &LayoutThreadData,
                                 request_images: bool)
                                 -> LayoutContext<'a> {
@@ -1069,7 +1069,7 @@ impl LayoutThread {
         // If the entire flow tree is invalid, then it will be reflowed anyhow.
         let ua_stylesheets = &*UA_STYLESHEETS;
         let ua_or_user_guard = ua_stylesheets.shared_lock.read();
-        let guards = ReadGuards {
+        let guards = StylesheetGuards {
             author: &author_guard,
             ua_or_user: &ua_or_user_guard,
         };
@@ -1353,7 +1353,7 @@ impl LayoutThread {
 
         let author_guard = AUTHOR_SHARED_LOCK.read();
         let ua_or_user_guard = UA_STYLESHEETS.shared_lock.read();
-        let guards = ReadGuards {
+        let guards = StylesheetGuards {
             author: &author_guard,
             ua_or_user: &ua_or_user_guard,
         };
diff --git a/components/style/context.rs b/components/style/context.rs
index 93dfde0932b..3a2926672ac 100644
--- a/components/style/context.rs
+++ b/components/style/context.rs
@@ -17,7 +17,7 @@ use parking_lot::RwLock;
 use selector_parser::PseudoElement;
 use selectors::matching::ElementSelectorFlags;
 use servo_config::opts;
-use shared_lock::ReadGuards;
+use shared_lock::StylesheetGuards;
 use std::collections::HashMap;
 use std::env;
 use std::fmt;
@@ -67,7 +67,7 @@ pub struct SharedStyleContext<'a> {
     pub stylist: Arc<Stylist>,
 
     /// Guards for pre-acquired locks
-    pub guards: ReadGuards<'a>,
+    pub guards: StylesheetGuards<'a>,
 
     /// The animations that are currently running.
     pub running_animations: Arc<RwLock<HashMap<OpaqueNode, Vec<Animation>>>>,
diff --git a/components/style/gecko/data.rs b/components/style/gecko/data.rs
index ad6a1d1629c..a1ef6db3e2e 100644
--- a/components/style/gecko/data.rs
+++ b/components/style/gecko/data.rs
@@ -13,7 +13,7 @@ use gecko_bindings::sugar::ownership::{HasBoxFFI, HasFFI, HasSimpleFFI};
 use media_queries::Device;
 use parking_lot::RwLock;
 use properties::ComputedValues;
-use shared_lock::{ReadGuards, SharedRwLockReadGuard};
+use shared_lock::{StylesheetGuards, SharedRwLockReadGuard};
 use std::collections::HashMap;
 use std::sync::Arc;
 use std::sync::mpsc::{Receiver, Sender, channel};
@@ -97,7 +97,7 @@ impl PerDocumentStyleDataImpl {
     pub fn flush_stylesheets(&mut self, guard: &SharedRwLockReadGuard) {
         if self.stylesheets_changed {
             let mut stylist = Arc::get_mut(&mut self.stylist).unwrap();
-            stylist.update(&self.stylesheets, &ReadGuards::same(guard), None, true);
+            stylist.update(&self.stylesheets, &StylesheetGuards::same(guard), None, true);
             self.stylesheets_changed = false;
         }
     }
diff --git a/components/style/properties/properties.mako.rs b/components/style/properties/properties.mako.rs
index 1ae30358efa..f9c2cac07b6 100644
--- a/components/style/properties/properties.mako.rs
+++ b/components/style/properties/properties.mako.rs
@@ -31,7 +31,7 @@ use parser::{Parse, ParserContext, ParserContextExtraData};
 use properties::animated_properties::TransitionProperty;
 #[cfg(feature = "servo")] use servo_config::prefs::PREFS;
 use servo_url::ServoUrl;
-use shared_lock::ReadGuards;
+use shared_lock::StylesheetGuards;
 use style_traits::ToCss;
 use stylesheets::Origin;
 #[cfg(feature = "servo")] use values::Either;
@@ -1861,7 +1861,7 @@ bitflags! {
 ///
 pub fn cascade(device: &Device,
                rule_node: &StrongRuleNode,
-               guards: &ReadGuards,
+               guards: &StylesheetGuards,
                parent_style: Option<<&ComputedValues>,
                layout_parent_style: Option<<&ComputedValues>,
                cascade_info: Option<<&mut CascadeInfo>,
diff --git a/components/style/rule_tree/mod.rs b/components/style/rule_tree/mod.rs
index 80aa88596d6..54cf785e458 100644
--- a/components/style/rule_tree/mod.rs
+++ b/components/style/rule_tree/mod.rs
@@ -11,7 +11,7 @@ use arc_ptr_eq;
 #[cfg(feature = "servo")]
 use heapsize::HeapSizeOf;
 use properties::{Importance, PropertyDeclarationBlock};
-use shared_lock::{Locked, ReadGuards, SharedRwLockReadGuard};
+use shared_lock::{Locked, StylesheetGuards, SharedRwLockReadGuard};
 use std::io::{self, Write};
 use std::ptr;
 use std::sync::Arc;
@@ -110,13 +110,13 @@ impl RuleTree {
         self.root.clone()
     }
 
-    fn dump<W: Write>(&self, guards: &ReadGuards, writer: &mut W) {
+    fn dump<W: Write>(&self, guards: &StylesheetGuards, writer: &mut W) {
         let _ = writeln!(writer, " + RuleTree");
         self.root.get().dump(guards, writer, 0);
     }
 
     /// Dump the rule tree to stdout.
-    pub fn dump_stdout(&self, guards: &ReadGuards) {
+    pub fn dump_stdout(&self, guards: &StylesheetGuards) {
         let mut stdout = io::stdout();
         self.dump(guards, &mut stdout);
     }
@@ -162,7 +162,7 @@ impl RuleTree {
                                 level: CascadeLevel,
                                 pdb: Option<&Arc<Locked<PropertyDeclarationBlock>>>,
                                 path: &StrongRuleNode,
-                                guards: &ReadGuards)
+                                guards: &StylesheetGuards)
                                 -> Option<StrongRuleNode> {
         debug_assert!(level.is_unique_per_element());
         // TODO(emilio): Being smarter with lifetimes we could avoid a bit of
@@ -282,7 +282,7 @@ pub enum CascadeLevel {
 
 impl CascadeLevel {
     /// Select a lock guard for this level
-    pub fn guard<'a>(&self, guards: &'a ReadGuards<'a>) -> &'a SharedRwLockReadGuard<'a> {
+    pub fn guard<'a>(&self, guards: &'a StylesheetGuards<'a>) -> &'a SharedRwLockReadGuard<'a> {
         match *self {
             CascadeLevel::UANormal |
             CascadeLevel::UserNormal |
@@ -435,7 +435,7 @@ impl RuleNode {
         }
     }
 
-    fn dump<W: Write>(&self, guards: &ReadGuards, writer: &mut W, indent: usize) {
+    fn dump<W: Write>(&self, guards: &StylesheetGuards, writer: &mut W, indent: usize) {
         const INDENT_INCREMENT: usize = 4;
 
         for _ in 0..indent {
diff --git a/components/style/shared_lock.rs b/components/style/shared_lock.rs
index c92ab9efccf..152e2b6ba82 100644
--- a/components/style/shared_lock.rs
+++ b/components/style/shared_lock.rs
@@ -180,7 +180,7 @@ pub trait ToCssWithGuard {
 
 /// Guards for a document
 #[derive(Clone)]
-pub struct ReadGuards<'a> {
+pub struct StylesheetGuards<'a> {
     /// For author-origin stylesheets
     pub author: &'a SharedRwLockReadGuard<'a>,
 
@@ -188,10 +188,10 @@ pub struct ReadGuards<'a> {
     pub ua_or_user: &'a SharedRwLockReadGuard<'a>,
 }
 
-impl<'a> ReadGuards<'a> {
+impl<'a> StylesheetGuards<'a> {
     /// Same guard for all origins
     pub fn same(guard: &'a SharedRwLockReadGuard<'a>) -> Self {
-        ReadGuards {
+        StylesheetGuards {
             author: guard,
             ua_or_user: guard,
         }
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index d58e0dd0e85..27d3dd4b10b 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -27,7 +27,7 @@ use selectors::matching::{AFFECTED_BY_STYLE_ATTRIBUTE, AFFECTED_BY_PRESENTATIONA
 use selectors::matching::{ElementSelectorFlags, StyleRelations, matches_complex_selector};
 use selectors::parser::{Selector, SimpleSelector, LocalName as LocalNameSelector, ComplexSelector};
 use selectors::parser::SelectorMethods;
-use shared_lock::{Locked, SharedRwLockReadGuard, ReadGuards};
+use shared_lock::{Locked, SharedRwLockReadGuard, StylesheetGuards};
 use sink::Push;
 use smallvec::VecLike;
 use std::borrow::Borrow;
@@ -158,7 +158,7 @@ impl Stylist {
     /// device is dirty, which means we need to re-evaluate media queries.
     pub fn update(&mut self,
                   doc_stylesheets: &[Arc<Stylesheet>],
-                  guards: &ReadGuards,
+                  guards: &StylesheetGuards,
                   ua_stylesheets: Option<&UserAgentStylesheets>,
                   stylesheets_changed: bool) -> bool {
         if !(self.is_device_dirty || stylesheets_changed) {
@@ -299,7 +299,7 @@ impl Stylist {
     /// values. The flow constructor uses this flag when constructing anonymous
     /// flows.
     pub fn precomputed_values_for_pseudo(&self,
-                                         guards: &ReadGuards,
+                                         guards: &StylesheetGuards,
                                          pseudo: &PseudoElement,
                                          parent: Option<&Arc<ComputedValues>>,
                                          cascade_flags: CascadeFlags)
@@ -345,7 +345,7 @@ impl Stylist {
     /// Returns the style for an anonymous box of the given type.
     #[cfg(feature = "servo")]
     pub fn style_for_anonymous_box(&self,
-                                   guards: &ReadGuards,
+                                   guards: &StylesheetGuards,
                                    pseudo: &PseudoElement,
                                    parent_style: &Arc<ComputedValues>)
                                    -> Arc<ComputedValues> {
@@ -382,7 +382,7 @@ impl Stylist {
     /// Check the documentation on lazy pseudo-elements in
     /// docs/components/style.md
     pub fn lazily_compute_pseudo_element_style<E>(&self,
-                                                  guards: &ReadGuards,
+                                                  guards: &StylesheetGuards,
                                                   element: &E,
                                                   pseudo: &PseudoElement,
                                                   parent: &Arc<ComputedValues>)
@@ -544,7 +544,7 @@ impl Stylist {
                                         style_attribute: Option<&Arc<Locked<PropertyDeclarationBlock>>>,
                                         animation_rules: AnimationRules,
                                         pseudo_element: Option<&PseudoElement>,
-                                        guards: &ReadGuards,
+                                        guards: &StylesheetGuards,
                                         applicable_declarations: &mut V,
                                         flags: &mut ElementSelectorFlags) -> StyleRelations
         where E: TElement +
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index 82cbd7aef74..177a6c076e8 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -74,7 +74,7 @@ use style::properties::parse_one_declaration;
 use style::restyle_hints::{self, RestyleHint};
 use style::selector_parser::PseudoElementCascadeType;
 use style::sequential;
-use style::shared_lock::{SharedRwLock, SharedRwLockReadGuard, ReadGuards, ToCssWithGuard, Locked};
+use style::shared_lock::{SharedRwLock, SharedRwLockReadGuard, StylesheetGuards, ToCssWithGuard, Locked};
 use style::string_cache::Atom;
 use style::stylesheets::{CssRule, CssRules, ImportRule, MediaRule, NamespaceRule};
 use style::stylesheets::{Origin, Stylesheet, StyleRule};
@@ -129,7 +129,7 @@ fn create_shared_context<'a>(guard: &'a SharedRwLockReadGuard,
 
     SharedStyleContext {
         stylist: per_doc_data.stylist.clone(),
-        guards: ReadGuards::same(guard),
+        guards: StylesheetGuards::same(guard),
         running_animations: per_doc_data.running_animations.clone(),
         expired_animations: per_doc_data.expired_animations.clone(),
         // FIXME(emilio): Stop boxing here.
@@ -642,7 +642,7 @@ pub extern "C" fn Servo_ComputedValues_GetForAnonymousBox(parent_style_or_null:
      -> ServoComputedValuesStrong {
     let global_style_data = &*GLOBAL_STYLE_DATA;
     let guard = global_style_data.shared_lock.read();
-    let guards = ReadGuards::same(&guard);
+    let guards = StylesheetGuards::same(&guard);
     let data = PerDocumentStyleData::from_ffi(raw_data).borrow_mut();
     let atom = Atom::from(pseudo_tag);
     let pseudo = PseudoElement::from_atom_unchecked(atom, /* anon_box = */ true);
@@ -699,7 +699,7 @@ fn get_pseudo_style(guard: &SharedRwLockReadGuard, element: GeckoElement, pseudo
         PseudoElementCascadeType::Lazy => {
             let d = doc_data.borrow_mut();
             let base = styles.primary.values();
-            let guards = ReadGuards::same(guard);
+            let guards = StylesheetGuards::same(guard);
             d.stylist.lazily_compute_pseudo_element_style(&guards,
                                                           &element,
                                                           &pseudo,