Auto merge of #13520 - bholley:atomic_refcell, r=emilio

Implement AtomicRefCell and use it for layout/style node data

See the rationale at https://bugzilla.mozilla.org/show_bug.cgi?id=1305141

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components/layout/construct.rs

@@ -16,7 +16,7 @@
 use app_units::Au;
 use block::BlockFlow;
 use context::LayoutContext;
-use data::{HAS_NEWLY_CONSTRUCTED_FLOW, PrivateLayoutData};
+use data::{HAS_NEWLY_CONSTRUCTED_FLOW, PersistentLayoutData};
 use flex::FlexFlow;
 use floats::FloatKind;
 use flow::{self, AbsoluteDescendants, IS_ABSOLUTELY_POSITIONED, ImmutableFlowUtils};
@@ -218,8 +218,8 @@ impl InlineFragmentsAccumulator {
             enclosing_node: Some(InlineFragmentNodeInfo {
                 address: node.opaque(),
                 pseudo: node.get_pseudo_element_type().strip(),
-                style: node.style(style_context).clone(),
+                style: node.style(style_context),
-                selected_style: node.selected_style(style_context).clone(),
+                selected_style: node.selected_style(style_context),
                 flags: InlineFragmentNodeFlags::empty(),
             }),
             bidi_control_chars: None,
@@ -355,12 +355,12 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
 
         let style_context = self.style_context();
         if child.is_table_cell() {
-            let mut style = child_node.style(style_context).clone();
+            let mut style = child_node.style(style_context);
             properties::modify_style_for_anonymous_table_object(&mut style, display::T::table_row);
             let fragment = Fragment::from_opaque_node_and_style(child_node.opaque(),
                                                                 PseudoElementType::Normal,
                                                                 style,
-                                                                child_node.selected_style(style_context).clone(),
+                                                                child_node.selected_style(style_context),
                                                                 child_node.restyle_damage(),
                                                                 SpecificFragmentInfo::TableRow);
             let mut new_child: FlowRef = Arc::new(TableRowFlow::from_fragment(fragment));
@@ -369,12 +369,12 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
             *child = new_child
         }
         if child.is_table_row() || child.is_table_rowgroup() {
-            let mut style = child_node.style(style_context).clone();
+            let mut style = child_node.style(style_context);
             properties::modify_style_for_anonymous_table_object(&mut style, display::T::table);
             let fragment = Fragment::from_opaque_node_and_style(child_node.opaque(),
                                                                 PseudoElementType::Normal,
                                                                 style,
-                                                                child_node.selected_style(style_context).clone(),
+                                                                child_node.selected_style(style_context),
                                                                 child_node.restyle_damage(),
                                                                 SpecificFragmentInfo::Table);
             let mut new_child: FlowRef = Arc::new(TableFlow::from_fragment(fragment));
@@ -383,13 +383,13 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
             *child = new_child
         }
         if child.is_table() {
-            let mut style = child_node.style(style_context).clone();
+            let mut style = child_node.style(style_context);
             properties::modify_style_for_anonymous_table_object(&mut style, display::T::table);
             let fragment =
                 Fragment::from_opaque_node_and_style(child_node.opaque(),
                                                      PseudoElementType::Normal,
                                                      style,
-                                                     child_node.selected_style(style_context).clone(),
+                                                     child_node.selected_style(style_context),
                                                      child_node.restyle_damage(),
                                                      SpecificFragmentInfo::TableWrapper);
             let mut new_child: FlowRef = Arc::new(TableWrapperFlow::from_fragment(fragment, None));
@@ -477,7 +477,7 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
             let (ascent, descent) =
                 inline_flow.compute_minimum_ascent_and_descent(&mut self.layout_context
                                                                         .font_context(),
-                                                               &**node.style(self.style_context()));
+                                                               &node.style(self.style_context()));
             inline_flow.minimum_block_size_above_baseline = ascent;
             inline_flow.minimum_depth_below_baseline = descent;
         }
@@ -589,7 +589,7 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
                 let fragment = Fragment::from_opaque_node_and_style(whitespace_node,
                                                                     whitespace_pseudo,
                                                                     whitespace_style,
-                                                                    node.selected_style(style_context).clone(),
+                                                                    node.selected_style(style_context),
                                                                     whitespace_damage,
                                                                     fragment_info);
                 inline_fragment_accumulator.fragments.fragments.push_back(fragment);
@@ -692,7 +692,7 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
                 }
             }
 
-            let mut style = node.style(self.style_context()).clone();
+            let mut style = node.style(self.style_context());
             if node_is_input_or_text_area {
                 style = self.style_context().stylist.
                     precomputed_values_for_pseudo(&PseudoElement::ServoInputText, Some(&style)).unwrap();
@@ -732,7 +732,7 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
                         node.opaque(),
                         node.get_pseudo_element_type().strip(),
                         style,
-                        selected_style.clone(),
+                        selected_style,
                         node.restyle_damage(),
                         specific_fragment_info))
             }
@@ -806,7 +806,7 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
                                                       -> ConstructionResult {
         let mut opt_inline_block_splits: LinkedList<InlineBlockSplit> = LinkedList::new();
         let mut fragment_accumulator = InlineFragmentsAccumulator::from_inline_node(node, self.style_context());
-        fragment_accumulator.bidi_control_chars = bidi_control_chars(&*node.style(self.style_context()));
+        fragment_accumulator.bidi_control_chars = bidi_control_chars(&node.style(self.style_context()));
 
         let mut abs_descendants = AbsoluteDescendants::new();
 
@@ -882,7 +882,7 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
                         Fragment::from_opaque_node_and_style(whitespace_node,
                                                              whitespace_pseudo,
                                                              whitespace_style,
-                                                             node.selected_style(self.style_context()).clone(),
+                                                             node.selected_style(self.style_context()),
                                                              whitespace_damage,
                                                              fragment_info);
                     fragment_accumulator.fragments.fragments.push_back(fragment)
@@ -905,7 +905,7 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
             let fragment = Fragment::from_opaque_node_and_style(node.opaque(),
                                                                 node.get_pseudo_element_type().strip(),
                                                                 modified_style,
-                                                                node.selected_style(self.style_context()).clone(),
+                                                                node.selected_style(self.style_context()),
                                                                 node.restyle_damage(),
                                                                 info);
             fragment_accumulator.fragments.fragments.push_back(fragment)
@@ -949,13 +949,13 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
             return ConstructionResult::ConstructionItem(ConstructionItem::Whitespace(
                 node.opaque(),
                 node.get_pseudo_element_type().strip(),
-                node.style(self.style_context()).clone(),
+                node.style(self.style_context()),
                 node.restyle_damage()))
         }
 
         // Modify the style as necessary. (See the comment in
         // `properties::modify_style_for_replaced_content()`.)
-        let mut style = node.style(self.style_context()).clone();
+        let mut style = node.style(self.style_context());
         match node.get_pseudo_element_type() {
             PseudoElementType::Before(_) |
             PseudoElementType::After(_) => {}
@@ -993,14 +993,14 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
         };
 
         let style_context = self.style_context();
-        let mut modified_style = (*node.style(self.style_context())).clone();
+        let mut modified_style = node.style(self.style_context());
         properties::modify_style_for_outer_inline_block_fragment(&mut modified_style);
         let fragment_info = SpecificFragmentInfo::InlineBlock(InlineBlockFragmentInfo::new(
                 block_flow));
         let fragment = Fragment::from_opaque_node_and_style(node.opaque(),
                                                             node.get_pseudo_element_type().strip(),
                                                             modified_style,
-                                                            node.selected_style(style_context).clone(),
+                                                            node.selected_style(style_context),
                                                             node.restyle_damage(),
                                                             fragment_info);
 
@@ -1030,12 +1030,12 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
         let fragment_info = SpecificFragmentInfo::InlineAbsoluteHypothetical(
             InlineAbsoluteHypotheticalFragmentInfo::new(block_flow));
         let style_context = self.style_context();
-        let mut style = node.style(style_context).clone();
+        let mut style = node.style(style_context);
         properties::modify_style_for_inline_absolute_hypothetical_fragment(&mut style);
         let fragment = Fragment::from_opaque_node_and_style(node.opaque(),
                                                             PseudoElementType::Normal,
                                                             style,
-                                                            node.selected_style(style_context).clone(),
+                                                            node.selected_style(style_context),
                                                             node.restyle_damage(),
                                                             fragment_info);
 
@@ -1412,7 +1412,7 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
 
         let mut set_has_newly_constructed_flow_flag = false;
         let result = {
-            let mut style = node.style(self.style_context()).clone();
+            let mut style = node.style(self.style_context());
             let mut data = node.mutate_layout_data().unwrap();
             let damage = data.restyle_damage;
 
@@ -1679,7 +1679,7 @@ trait NodeUtils {
     /// Returns true if this node doesn't render its kids and false otherwise.
     fn is_replaced_content(&self) -> bool;
 
-    fn construction_result_mut(self, layout_data: &mut PrivateLayoutData) -> &mut ConstructionResult;
+    fn construction_result_mut(self, layout_data: &mut PersistentLayoutData) -> &mut ConstructionResult;
 
     /// Sets the construction result of a flow.
     fn set_flow_construction_result(self, result: ConstructionResult);
@@ -1708,7 +1708,7 @@ impl<ConcreteThreadSafeLayoutNode> NodeUtils for ConcreteThreadSafeLayoutNode
         }
     }
 
-    fn construction_result_mut(self, data: &mut PrivateLayoutData) -> &mut ConstructionResult {
+    fn construction_result_mut(self, data: &mut PersistentLayoutData) -> &mut ConstructionResult {
         match self.get_pseudo_element_type() {
             PseudoElementType::Before(_) => &mut data.before_flow_construction_result,
             PseudoElementType::After (_) => &mut data.after_flow_construction_result,

components/layout/data.rs

@@ -4,15 +4,15 @@
 
 use construct::ConstructionResult;
 use script_layout_interface::restyle_damage::RestyleDamage;
-use style::data::PrivateStyleData;
+use style::data::PersistentStyleData;
 
 /// Data that layout associates with a node.
-pub struct PrivateLayoutData {
+pub struct PersistentLayoutData {
     /// Data that the style system associates with a node. When the
     /// style system is being used standalone, this is all that hangs
     /// off the node. This must be first to permit the various
-    /// transmuations between PrivateStyleData PrivateLayoutData.
+    /// transmutations between PersistentStyleData and PersistentLayoutData.
-    pub style_data: PrivateStyleData,
+    pub style_data: PersistentStyleData,
 
     /// Description of how to account for recent style changes.
     pub restyle_damage: RestyleDamage,
@@ -34,11 +34,11 @@ pub struct PrivateLayoutData {
     pub flags: LayoutDataFlags,
 }
 
-impl PrivateLayoutData {
+impl PersistentLayoutData {
     /// Creates new layout data.
-    pub fn new() -> PrivateLayoutData {
+    pub fn new() -> PersistentLayoutData {
-        PrivateLayoutData {
+        PersistentLayoutData {
-            style_data: PrivateStyleData::new(),
+            style_data: PersistentStyleData::new(),
             restyle_damage: RestyleDamage::empty(),
             flow_construction_result: ConstructionResult::None,
             before_flow_construction_result: ConstructionResult::None,

components/layout/flow.rs

@@ -1272,7 +1272,7 @@ impl<'a> ImmutableFlowUtils for &'a Flow {
     /// as it's harder to understand.
     fn generate_missing_child_flow<N: ThreadSafeLayoutNode>(self, node: &N, ctx: &LayoutContext) -> FlowRef {
         let style_context = ctx.style_context();
-        let mut style = node.style(style_context).clone();
+        let mut style = node.style(style_context);
         match self.class() {
             FlowClass::Table | FlowClass::TableRowGroup => {
                 properties::modify_style_for_anonymous_table_object(
@@ -1282,7 +1282,7 @@ impl<'a> ImmutableFlowUtils for &'a Flow {
                     node.opaque(),
                     PseudoElementType::Normal,
                     style,
-                    node.selected_style(style_context).clone(),
+                    node.selected_style(style_context),
                     node.restyle_damage(),
                     SpecificFragmentInfo::TableRow);
                 Arc::new(TableRowFlow::from_fragment(fragment))
@@ -1295,7 +1295,7 @@ impl<'a> ImmutableFlowUtils for &'a Flow {
                     node.opaque(),
                     PseudoElementType::Normal,
                     style,
-                    node.selected_style(style_context).clone(),
+                    node.selected_style(style_context),
                     node.restyle_damage(),
                     SpecificFragmentInfo::TableCell);
                 let hide = node.style(style_context).get_inheritedtable().empty_cells == empty_cells::T::hide;
@@ -1309,7 +1309,7 @@ impl<'a> ImmutableFlowUtils for &'a Flow {
                     Fragment::from_opaque_node_and_style(node.opaque(),
                                                          PseudoElementType::Normal,
                                                          style,
-                                                         node.selected_style(style_context).clone(),
+                                                         node.selected_style(style_context),
                                                          node.restyle_damage(),
                                                          SpecificFragmentInfo::Generic);
                 Arc::new(BlockFlow::from_fragment(fragment, None))

components/layout/fragment.rs

@@ -856,7 +856,7 @@ impl Fragment {
     /// Constructs a new `Fragment` instance.
     pub fn new<N: ThreadSafeLayoutNode>(node: &N, specific: SpecificFragmentInfo, ctx: &LayoutContext) -> Fragment {
         let style_context = ctx.style_context();
-        let style = node.style(style_context).clone();
+        let style = node.style(style_context);
         let writing_mode = style.writing_mode;
 
         let mut restyle_damage = node.restyle_damage();
@@ -865,7 +865,7 @@ impl Fragment {
         Fragment {
             node: node.opaque(),
             style: style,
-            selected_style: node.selected_style(style_context).clone(),
+            selected_style: node.selected_style(style_context),
             restyle_damage: restyle_damage,
             border_box: LogicalRect::zero(writing_mode),
             border_padding: LogicalMargin::zero(writing_mode),

components/layout/wrapper.rs

@@ -31,33 +31,25 @@
 #![allow(unsafe_code)]
 
 use core::nonzero::NonZero;
-use data::{LayoutDataFlags, PrivateLayoutData};
+use data::{LayoutDataFlags, PersistentLayoutData};
-use script_layout_interface::{OpaqueStyleAndLayoutData, PartialStyleAndLayoutData};
+use script_layout_interface::{OpaqueStyleAndLayoutData, PartialPersistentLayoutData};
 use script_layout_interface::wrapper_traits::{LayoutNode, ThreadSafeLayoutNode};
+use style::atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
 use style::computed_values::content::{self, ContentItem};
-use style::refcell::{Ref, RefCell, RefMut};
 
-pub type NonOpaqueStyleAndLayoutData = *mut RefCell<PrivateLayoutData>;
+pub type NonOpaqueStyleAndLayoutData = *mut AtomicRefCell<PersistentLayoutData>;
 
 pub trait LayoutNodeLayoutData {
-    /// Similar to borrow_data*, but returns the full PrivateLayoutData rather
+    /// Similar to borrow_data*, but returns the full PersistentLayoutData rather
-    /// than only the PrivateStyleData.
+    /// than only the PersistentStyleData.
-    unsafe fn borrow_layout_data_unchecked(&self) -> Option<*const PrivateLayoutData>;
+    fn borrow_layout_data(&self) -> Option<AtomicRef<PersistentLayoutData>>;
-    fn borrow_layout_data(&self) -> Option<Ref<PrivateLayoutData>>;
+    fn mutate_layout_data(&self) -> Option<AtomicRefMut<PersistentLayoutData>>;
-    fn mutate_layout_data(&self) -> Option<RefMut<PrivateLayoutData>>;
     fn initialize_data(self);
     fn flow_debug_id(self) -> usize;
 }
 
 impl<T: LayoutNode> LayoutNodeLayoutData for T {
-    unsafe fn borrow_layout_data_unchecked(&self) -> Option<*const PrivateLayoutData> {
+    fn borrow_layout_data(&self) -> Option<AtomicRef<PersistentLayoutData>> {
-        self.get_style_and_layout_data().map(|opaque| {
-            let container = *opaque.ptr as NonOpaqueStyleAndLayoutData;
-            &(*(*container).as_unsafe_cell().get()) as *const PrivateLayoutData
-        })
-    }
-
-    fn borrow_layout_data(&self) -> Option<Ref<PrivateLayoutData>> {
         unsafe {
             self.get_style_and_layout_data().map(|opaque| {
                 let container = *opaque.ptr as NonOpaqueStyleAndLayoutData;
@@ -66,7 +58,7 @@ impl<T: LayoutNode> LayoutNodeLayoutData for T {
         }
     }
 
-    fn mutate_layout_data(&self) -> Option<RefMut<PrivateLayoutData>> {
+    fn mutate_layout_data(&self) -> Option<AtomicRefMut<PersistentLayoutData>> {
         unsafe {
             self.get_style_and_layout_data().map(|opaque| {
                 let container = *opaque.ptr as NonOpaqueStyleAndLayoutData;
@@ -76,11 +68,11 @@ impl<T: LayoutNode> LayoutNodeLayoutData for T {
     }
 
     fn initialize_data(self) {
-        if unsafe { self.borrow_data_unchecked() }.is_none() {
+        if self.borrow_data().is_none() {
             let ptr: NonOpaqueStyleAndLayoutData =
-                Box::into_raw(box RefCell::new(PrivateLayoutData::new()));
+                Box::into_raw(box AtomicRefCell::new(PersistentLayoutData::new()));
             let opaque = OpaqueStyleAndLayoutData {
-                ptr: unsafe { NonZero::new(ptr as *mut RefCell<PartialStyleAndLayoutData>) }
+                ptr: unsafe { NonZero::new(ptr as *mut AtomicRefCell<PartialPersistentLayoutData>) }
             };
             self.init_style_and_layout_data(opaque);
         }
@@ -94,19 +86,17 @@ impl<T: LayoutNode> LayoutNodeLayoutData for T {
 pub trait ThreadSafeLayoutNodeHelpers {
     fn flow_debug_id(self) -> usize;
 
-    unsafe fn borrow_layout_data_unchecked(&self) -> Option<*const PrivateLayoutData>;
-
     /// Borrows the layout data immutably. Fails on a conflicting borrow.
     ///
     /// TODO(pcwalton): Make this private. It will let us avoid borrow flag checks in some cases.
     #[inline(always)]
-    fn borrow_layout_data(&self) -> Option<Ref<PrivateLayoutData>>;
+    fn borrow_layout_data(&self) -> Option<AtomicRef<PersistentLayoutData>>;
 
     /// Borrows the layout data mutably. Fails on a conflicting borrow.
     ///
     /// TODO(pcwalton): Make this private. It will let us avoid borrow flag checks in some cases.
     #[inline(always)]
-    fn mutate_layout_data(&self) -> Option<RefMut<PrivateLayoutData>>;
+    fn mutate_layout_data(&self) -> Option<AtomicRefMut<PersistentLayoutData>>;
 
     /// Returns the layout data flags for this node.
     fn flags(self) -> LayoutDataFlags;
@@ -129,14 +119,7 @@ impl<T: ThreadSafeLayoutNode> ThreadSafeLayoutNodeHelpers for T {
         self.borrow_layout_data().map_or(0, |d| d.flow_construction_result.debug_id())
     }
 
-    unsafe fn borrow_layout_data_unchecked(&self) -> Option<*const PrivateLayoutData> {
+    fn borrow_layout_data(&self) -> Option<AtomicRef<PersistentLayoutData>> {
-        self.get_style_and_layout_data().map(|opaque| {
-            let container = *opaque.ptr as NonOpaqueStyleAndLayoutData;
-            &(*(*container).as_unsafe_cell().get()) as *const PrivateLayoutData
-        })
-    }
-
-    fn borrow_layout_data(&self) -> Option<Ref<PrivateLayoutData>> {
         unsafe {
             self.get_style_and_layout_data().map(|opaque| {
                 let container = *opaque.ptr as NonOpaqueStyleAndLayoutData;
@@ -145,7 +128,7 @@ impl<T: ThreadSafeLayoutNode> ThreadSafeLayoutNodeHelpers for T {
         }
     }
 
-    fn mutate_layout_data(&self) -> Option<RefMut<PrivateLayoutData>> {
+    fn mutate_layout_data(&self) -> Option<AtomicRefMut<PersistentLayoutData>> {
         unsafe {
             self.get_style_and_layout_data().map(|opaque| {
                 let container = *opaque.ptr as NonOpaqueStyleAndLayoutData;
@@ -155,9 +138,7 @@ impl<T: ThreadSafeLayoutNode> ThreadSafeLayoutNodeHelpers for T {
     }
 
     fn flags(self) -> LayoutDataFlags {
-        unsafe {
+            self.borrow_layout_data().as_ref().unwrap().flags
-            (*self.borrow_layout_data_unchecked().unwrap()).flags
-        }
     }
 
     fn insert_flags(self, new_flags: LayoutDataFlags) {

components/layout_thread/lib.rs

@@ -86,7 +86,7 @@ use profile_traits::mem::{self, Report, ReportKind, ReportsChan};
 use profile_traits::time::{self, TimerMetadata, profile};
 use profile_traits::time::{TimerMetadataFrameType, TimerMetadataReflowType};
 use script::layout_wrapper::{ServoLayoutDocument, ServoLayoutNode};
-use script_layout_interface::{OpaqueStyleAndLayoutData, PartialStyleAndLayoutData};
+use script_layout_interface::{OpaqueStyleAndLayoutData, PartialPersistentLayoutData};
 use script_layout_interface::message::{Msg, NewLayoutThreadInfo, Reflow, ReflowQueryType, ScriptReflow};
 use script_layout_interface::reporter::CSSErrorReporter;
 use script_layout_interface::restyle_damage::{REFLOW, REFLOW_OUT_OF_FLOW, REPAINT, REPOSITION};
@@ -104,6 +104,7 @@ use std::sync::{Arc, Mutex, MutexGuard, RwLock};
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::mpsc::{Receiver, Sender, channel};
 use style::animation::Animation;
+use style::atomic_refcell::AtomicRefCell;
 use style::computed_values::{filter, mix_blend_mode};
 use style::context::{LocalStyleContextCreationInfo, ReflowGoal, SharedStyleContext};
 use style::dom::{TDocument, TElement, TNode};
@@ -112,7 +113,6 @@ use style::logical_geometry::LogicalPoint;
 use style::media_queries::{Device, MediaType};
 use style::parallel::WorkQueueData;
 use style::parser::ParserContextExtraData;
-use style::refcell::RefCell;
 use style::selector_matching::Stylist;
 use style::stylesheets::{CSSRuleIteratorExt, Origin, Stylesheet, UserAgentStylesheets};
 use style::thread_state;
@@ -1594,7 +1594,7 @@ impl LayoutThread {
     /// Handles a message to destroy layout data. Layout data must be destroyed on *this* thread
     /// because the struct type is transmuted to a different type on the script side.
     unsafe fn handle_reap_style_and_layout_data(&self, data: OpaqueStyleAndLayoutData) {
-        let ptr: *mut RefCell<PartialStyleAndLayoutData> = *data.ptr;
+        let ptr: *mut AtomicRefCell<PartialPersistentLayoutData> = *data.ptr;
         let non_opaque: NonOpaqueStyleAndLayoutData = ptr as *mut _;
         let _ = Box::from_raw(non_opaque);
     }

components/script/layout_wrapper.rs

@@ -43,7 +43,7 @@ use gfx_traits::ByteIndex;
 use msg::constellation_msg::PipelineId;
 use range::Range;
 use script_layout_interface::{HTMLCanvasData, LayoutNodeType, TrustedNodeAddress};
-use script_layout_interface::{OpaqueStyleAndLayoutData, PartialStyleAndLayoutData};
+use script_layout_interface::{OpaqueStyleAndLayoutData, PartialPersistentLayoutData};
 use script_layout_interface::restyle_damage::RestyleDamage;
 use script_layout_interface::wrapper_traits::{DangerousThreadSafeLayoutNode, LayoutNode, PseudoElementType};
 use script_layout_interface::wrapper_traits::{ThreadSafeLayoutElement, ThreadSafeLayoutNode};
@@ -54,15 +54,15 @@ use std::marker::PhantomData;
 use std::mem::transmute;
 use std::sync::Arc;
 use string_cache::{Atom, Namespace};
+use style::atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
 use style::attr::AttrValue;
 use style::computed_values::display;
 use style::context::SharedStyleContext;
-use style::data::PrivateStyleData;
+use style::data::PersistentStyleData;
 use style::dom::{LayoutIterator, NodeInfo, OpaqueNode, PresentationalHintsSynthetizer, TDocument, TElement, TNode};
 use style::dom::UnsafeNode;
 use style::element_state::*;
 use style::properties::{ComputedValues, PropertyDeclarationBlock};
-use style::refcell::{Ref, RefCell, RefMut};
 use style::selector_impl::{ElementSnapshot, NonTSPseudoClass, PseudoElement, ServoSelectorImpl};
 use style::selector_matching::ApplicableDeclarationBlock;
 use style::sink::Push;
@@ -220,30 +220,20 @@ impl<'ln> TNode for ServoLayoutNode<'ln> {
         self.node.set_flag(CAN_BE_FRAGMENTED, value)
     }
 
-    unsafe fn borrow_data_unchecked(&self) -> Option<*const PrivateStyleData> {
+    fn borrow_data(&self) -> Option<AtomicRef<PersistentStyleData>> {
-        self.get_style_data().map(|d| {
+        self.get_style_data().map(|d| d.borrow())
-            &(*d.as_unsafe_cell().get()).style_data as *const _
-        })
     }
 
-    fn borrow_data(&self) -> Option<Ref<PrivateStyleData>> {
+    fn mutate_data(&self) -> Option<AtomicRefMut<PersistentStyleData>> {
-        self.get_style_data().map(|d| {
+        self.get_style_data().map(|d| d.borrow_mut())
-            Ref::map(d.borrow(), |d| &d.style_data)
-        })
-    }
-
-    fn mutate_data(&self) -> Option<RefMut<PrivateStyleData>> {
-        self.get_style_data().map(|d| {
-            RefMut::map(d.borrow_mut(), |d| &mut d.style_data)
-        })
     }
 
     fn restyle_damage(self) -> RestyleDamage {
-        self.get_style_data().unwrap().borrow().restyle_damage
+        self.get_partial_layout_data().unwrap().borrow().restyle_damage
     }
 
     fn set_restyle_damage(self, damage: RestyleDamage) {
-        self.get_style_data().unwrap().borrow_mut().restyle_damage = damage;
+        self.get_partial_layout_data().unwrap().borrow_mut().restyle_damage = damage;
     }
 
     fn parent_node(&self) -> Option<ServoLayoutNode<'ln>> {
@@ -309,10 +299,12 @@ impl<'ln> LayoutNode for ServoLayoutNode<'ln> {
         self.script_type_id().into()
     }
 
-    fn get_style_data(&self) -> Option<&RefCell<PartialStyleAndLayoutData>> {
+    fn get_style_data(&self) -> Option<&AtomicRefCell<PersistentStyleData>> {
         unsafe {
             self.get_jsmanaged().get_style_and_layout_data().map(|d| {
-                &**d.ptr
+                let ppld: &AtomicRefCell<PartialPersistentLayoutData> = &**d.ptr;
+                let psd: &AtomicRefCell<PersistentStyleData> = transmute(ppld);
+                psd
             })
         }
     }
@@ -331,6 +323,14 @@ impl<'ln> LayoutNode for ServoLayoutNode<'ln> {
 }
 
 impl<'ln> ServoLayoutNode<'ln> {
+    fn get_partial_layout_data(&self) -> Option<&AtomicRefCell<PartialPersistentLayoutData>> {
+        unsafe {
+            self.get_jsmanaged().get_style_and_layout_data().map(|d| {
+                &**d.ptr
+            })
+        }
+    }
+
     fn dump_indent(self, indent: u32) {
         let mut s = String::new();
         for _ in 0..indent {
@@ -871,7 +871,7 @@ impl<'ln> ThreadSafeLayoutNode for ServoThreadSafeLayoutNode<'ln> {
         }
     }
 
-    fn get_style_data(&self) -> Option<&RefCell<PartialStyleAndLayoutData>> {
+    fn get_style_data(&self) -> Option<&AtomicRefCell<PersistentStyleData>> {
         self.node.get_style_data()
     }
 }

components/script_layout_interface/lib.rs

@@ -52,11 +52,11 @@ use core::nonzero::NonZero;
 use ipc_channel::ipc::IpcSender;
 use libc::c_void;
 use restyle_damage::RestyleDamage;
-use style::data::PrivateStyleData;
+use style::atomic_refcell::AtomicRefCell;
-use style::refcell::RefCell;
+use style::data::PersistentStyleData;
 
-pub struct PartialStyleAndLayoutData {
+pub struct PartialPersistentLayoutData {
-    pub style_data: PrivateStyleData,
+    pub style_data: PersistentStyleData,
     pub restyle_damage: RestyleDamage,
 }
 
@@ -64,7 +64,7 @@ pub struct PartialStyleAndLayoutData {
 pub struct OpaqueStyleAndLayoutData {
     #[ignore_heap_size_of = "TODO(#6910) Box value that should be counted but \
                              the type lives in layout"]
-    pub ptr: NonZero<*mut RefCell<PartialStyleAndLayoutData>>
+    pub ptr: NonZero<*mut AtomicRefCell<PartialPersistentLayoutData>>
 }
 
 #[allow(unsafe_code)]

components/script_layout_interface/wrapper_traits.rs

@@ -5,7 +5,6 @@
 use HTMLCanvasData;
 use LayoutNodeType;
 use OpaqueStyleAndLayoutData;
-use PartialStyleAndLayoutData;
 use gfx_traits::{ByteIndex, LayerId, LayerType};
 use msg::constellation_msg::PipelineId;
 use range::Range;
@@ -13,12 +12,13 @@ use restyle_damage::RestyleDamage;
 use std::fmt::Debug;
 use std::sync::Arc;
 use string_cache::{Atom, Namespace};
+use style::atomic_refcell::AtomicRefCell;
 use style::computed_values::display;
 use style::context::SharedStyleContext;
+use style::data::PersistentStyleData;
 use style::dom::{LayoutIterator, NodeInfo, PresentationalHintsSynthetizer, TNode};
 use style::dom::OpaqueNode;
 use style::properties::ServoComputedValues;
-use style::refcell::{Ref, RefCell};
 use style::selector_impl::{PseudoElement, PseudoElementCascadeType, ServoSelectorImpl};
 use url::Url;
 
@@ -76,7 +76,7 @@ pub trait LayoutNode: TNode {
     /// Returns the type ID of this node.
     fn type_id(&self) -> LayoutNodeType;
 
-    fn get_style_data(&self) -> Option<&RefCell<PartialStyleAndLayoutData>>;
+    fn get_style_data(&self) -> Option<&AtomicRefCell<PersistentStyleData>>;
 
     fn init_style_and_layout_data(&self, data: OpaqueStyleAndLayoutData);
     fn get_style_and_layout_data(&self) -> Option<OpaqueStyleAndLayoutData>;
@@ -183,7 +183,6 @@ pub trait ThreadSafeLayoutNode: Clone + Copy + NodeInfo + PartialEq + Sized {
         if self.get_style_data()
                .unwrap()
                .borrow()
-               .style_data
                .per_pseudo
                .contains_key(&PseudoElement::Before) {
             Some(self.with_pseudo(PseudoElementType::Before(None)))
@@ -197,7 +196,6 @@ pub trait ThreadSafeLayoutNode: Clone + Copy + NodeInfo + PartialEq + Sized {
         if self.get_style_data()
                .unwrap()
                .borrow()
-               .style_data
                .per_pseudo
                .contains_key(&PseudoElement::After) {
             Some(self.with_pseudo(PseudoElementType::After(None)))
@@ -240,12 +238,11 @@ pub trait ThreadSafeLayoutNode: Clone + Copy + NodeInfo + PartialEq + Sized {
     ///
     /// Unlike the version on TNode, this handles pseudo-elements.
     #[inline]
-    fn style(&self, context: &SharedStyleContext) -> Ref<Arc<ServoComputedValues>> {
+    fn style(&self, context: &SharedStyleContext) -> Arc<ServoComputedValues> {
         match self.get_pseudo_element_type() {
             PseudoElementType::Normal => {
-                Ref::map(self.get_style_data().unwrap().borrow(), |data| {
+                self.get_style_data().unwrap().borrow()
-                    data.style_data.style.as_ref().unwrap()
+                    .style.as_ref().unwrap().clone()
-                })
             },
             other => {
                 // Precompute non-eagerly-cascaded pseudo-element styles if not
@@ -258,14 +255,13 @@ pub trait ThreadSafeLayoutNode: Clone + Copy + NodeInfo + PartialEq + Sized {
                         if !self.get_style_data()
                                 .unwrap()
                                 .borrow()
-                                .style_data
                                 .per_pseudo.contains_key(&style_pseudo) {
                             let mut data = self.get_style_data().unwrap().borrow_mut();
                             let new_style =
                                 context.stylist
                                        .precomputed_values_for_pseudo(&style_pseudo,
-                                                                      data.style_data.style.as_ref());
+                                                                      data.style.as_ref());
-                            data.style_data.per_pseudo
+                            data.per_pseudo
                                 .insert(style_pseudo.clone(), new_style.unwrap());
                         }
                     }
@@ -274,7 +270,6 @@ pub trait ThreadSafeLayoutNode: Clone + Copy + NodeInfo + PartialEq + Sized {
                         if !self.get_style_data()
                                 .unwrap()
                                 .borrow()
-                                .style_data
                                 .per_pseudo.contains_key(&style_pseudo) {
                             let mut data = self.get_style_data().unwrap().borrow_mut();
                             let new_style =
@@ -282,16 +277,16 @@ pub trait ThreadSafeLayoutNode: Clone + Copy + NodeInfo + PartialEq + Sized {
                                        .lazily_compute_pseudo_element_style(
                                            &self.as_element(),
                                            &style_pseudo,
-                                           data.style_data.style.as_ref().unwrap());
+                                           data.style.as_ref().unwrap());
-                            data.style_data.per_pseudo
+                            data.per_pseudo
                                 .insert(style_pseudo.clone(), new_style.unwrap());
                         }
                     }
                 }
 
-                Ref::map(self.get_style_data().unwrap().borrow(), |data| {
+                self.get_style_data().unwrap().borrow()
-                    data.style_data.per_pseudo.get(&style_pseudo).unwrap()
+                    .per_pseudo.get(&style_pseudo)
-                })
+                    .unwrap().clone()
             }
         }
     }
@@ -304,24 +299,22 @@ pub trait ThreadSafeLayoutNode: Clone + Copy + NodeInfo + PartialEq + Sized {
     /// This should be used just for querying layout, or when we know the
     /// element style is precomputed, not from general layout itself.
     #[inline]
-    fn resolved_style(&self) -> Ref<Arc<ServoComputedValues>> {
+    fn resolved_style(&self) -> Arc<ServoComputedValues> {
-        Ref::map(self.get_style_data().unwrap().borrow(), |data| {
+        let data = self.get_style_data().unwrap().borrow();
-            match self.get_pseudo_element_type() {
+        match self.get_pseudo_element_type() {
-                PseudoElementType::Normal
+            PseudoElementType::Normal
-                    => data.style_data.style.as_ref().unwrap(),
+                => data.style.as_ref().unwrap().clone(),
-                other
+            other
-                    => data.style_data.per_pseudo.get(&other.style_pseudo_element()).unwrap(),
+                => data.per_pseudo.get(&other.style_pseudo_element()).unwrap().clone(),
-            }
+        }
-        })
     }
 
     #[inline]
-    fn selected_style(&self, _context: &SharedStyleContext) -> Ref<Arc<ServoComputedValues>> {
+    fn selected_style(&self, _context: &SharedStyleContext) -> Arc<ServoComputedValues> {
-        Ref::map(self.get_style_data().unwrap().borrow(), |data| {
+        let data = self.get_style_data().unwrap().borrow();
-            data.style_data.per_pseudo
+        data.per_pseudo
-                .get(&PseudoElement::Selection)
+            .get(&PseudoElement::Selection)
-                .unwrap_or(data.style_data.style.as_ref().unwrap())
+            .unwrap_or(data.style.as_ref().unwrap()).clone()
-        })
     }
 
     /// Removes the style from this node.
@@ -332,10 +325,10 @@ pub trait ThreadSafeLayoutNode: Clone + Copy + NodeInfo + PartialEq + Sized {
 
         match self.get_pseudo_element_type() {
             PseudoElementType::Normal => {
-                data.style_data.style = None;
+                data.style = None;
             }
             other => {
-                data.style_data.per_pseudo.remove(&other.style_pseudo_element());
+                data.per_pseudo.remove(&other.style_pseudo_element());
             }
         };
     }
@@ -390,7 +383,7 @@ pub trait ThreadSafeLayoutNode: Clone + Copy + NodeInfo + PartialEq + Sized {
         LayerId::new_of_type(LayerType::OverflowScroll, self.opaque().id() as usize)
     }
 
-    fn get_style_data(&self) -> Option<&RefCell<PartialStyleAndLayoutData>>;
+    fn get_style_data(&self) -> Option<&AtomicRefCell<PersistentStyleData>>;
 }
 
 // This trait is only public so that it can be implemented by the gecko wrapper.

components/servo/Cargo.lock

@@ -1728,6 +1728,32 @@ dependencies = [
  "shared_library 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "owning_ref"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "parking_lot"
+version = "0.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "owning_ref 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "parking_lot_core 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "parking_lot_core"
+version = "0.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "kernel32-sys 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.16 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
+ "smallvec 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "phf"
 version = "0.7.16"
@@ -2312,6 +2338,7 @@ dependencies = [
  "num-traits 0.1.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "num_cpus 0.2.13 (registry+https://github.com/rust-lang/crates.io-index)",
  "ordered-float 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "parking_lot 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "plugins 0.0.1",
  "quickersort 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2937,6 +2964,9 @@ dependencies = [
 "checksum osmesa-src 12.0.1 (git+https://github.com/servo/osmesa-src)" = "<none>"
 "checksum osmesa-sys 0.1.2 (git+https://github.com/daggerbot/osmesa-rs)" = "<none>"
 "checksum osmesa-sys 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "88cfece6e95d2e717e0872a7f53a8684712ad13822a7979bc760b9c77ec0013b"
+"checksum owning_ref 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "88084505837507cbec6a9f39b5d3b985db3c84e9a741c80200b619001283293d"
+"checksum parking_lot 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "3562f3de7bdff194212be82366abf5c6565aff8a433b71c53c63d0e7c9913878"
+"checksum parking_lot_core 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)" = "06f24c980718110494e9cfb7db7438895c3f54505101bb6170329d5e43a53f64"
 "checksum phf 0.7.16 (registry+https://github.com/rust-lang/crates.io-index)" = "52c875926de24c01b5b69153eaa258b57920a39b44bbce8ef1f2052a6c5a6a1a"
 "checksum phf_codegen 0.7.16 (registry+https://github.com/rust-lang/crates.io-index)" = "0a8912c2cc0ea2e8ae70388ec0af9a445e7ab37b3c9cc61f059c2b34db8ed50b"
 "checksum phf_generator 0.7.16 (registry+https://github.com/rust-lang/crates.io-index)" = "04b5ea825e28cb6efd89d9133b129b2003b45a221aeda025509b125b00ecb7c4"

components/style/Cargo.toml

@@ -39,6 +39,7 @@ num-integer = "0.1.32"
 num-traits = "0.1.32"
 num_cpus = "0.2.2"
 ordered-float = "0.2.2"
+parking_lot = "0.3.3"
 quickersort = "2.0.0"
 rand = "0.3"
 rustc-serialize = "0.3"

components/style/atomic_refcell.rs

@@ -0,0 +1,41 @@
+/* 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 parking_lot::{RwLock, RwLockReadGuard, RwLockWriteGuard};
+
+/// Container type providing RefCell-like semantics for objects shared across
+/// threads.
+///
+/// RwLock is traditionally considered to be the |Sync| analogue of RefCell.
+/// However, for consumers that can guarantee that they will never mutably
+/// borrow the contents concurrently with immutable borrows, an RwLock feels
+/// like overkill.
+///
+/// The RwLock in the standard library is indeed heavyweight, since it heap-
+/// allocates an OS-specific primitive and delegates operations to it. However,
+/// parking_lot provides a pure-rust implementation of the standard
+/// synchronization primitives, with uncontended borrows compiling down to a
+/// single atomic operation. This is exactly how we would build an atomic
+/// RefCell, so we newtype it with some API sugar.
+pub struct AtomicRefCell<T>(RwLock<T>);
+
+pub type AtomicRef<'a, T> = RwLockReadGuard<'a, T>;
+pub type AtomicRefMut<'a, T> = RwLockWriteGuard<'a, T>;
+impl<T> AtomicRefCell<T> {
+    pub fn new(value: T) -> Self {
+        AtomicRefCell(RwLock::new(value))
+    }
+    pub fn borrow(&self) -> AtomicRef<T> {
+        self.0.try_read().unwrap()
+    }
+    pub fn borrow_mut(&self) -> AtomicRefMut<T> {
+        self.0.try_write().unwrap()
+    }
+}
+
+impl<T: Default> Default for AtomicRefCell<T> {
+    fn default() -> Self {
+        Self::new(T::default())
+    }
+}

components/style/data.rs

@@ -11,7 +11,7 @@ use std::hash::BuildHasherDefault;
 use std::sync::Arc;
 use std::sync::atomic::AtomicIsize;
 
-pub struct PrivateStyleData {
+pub struct PersistentStyleData {
     /// The results of CSS styling for this node.
     pub style: Option<Arc<ComputedValues>>,
 
@@ -23,9 +23,9 @@ pub struct PrivateStyleData {
     pub parallel: DomParallelInfo,
 }
 
-impl PrivateStyleData {
+impl PersistentStyleData {
     pub fn new() -> Self {
-        PrivateStyleData {
+        PersistentStyleData {
             style: None,
             per_pseudo: HashMap::with_hasher(Default::default()),
             parallel: DomParallelInfo::new(),

components/style/dom.rs

@@ -6,11 +6,10 @@
 
 #![allow(unsafe_code)]
 
-use context::SharedStyleContext;
+use atomic_refcell::{AtomicRef, AtomicRefMut};
-use data::PrivateStyleData;
+use data::PersistentStyleData;
 use element_state::ElementState;
 use properties::{ComputedValues, PropertyDeclarationBlock};
-use refcell::{Ref, RefMut};
 use restyle_hints::{RESTYLE_DESCENDANTS, RESTYLE_LATER_SIBLINGS, RESTYLE_SELF, RestyleHint};
 use selector_impl::{ElementExt, PseudoElement};
 use selector_matching::ApplicableDeclarationBlock;
@@ -139,17 +138,13 @@ pub trait TNode : Sized + Copy + Clone + NodeInfo {
 
     unsafe fn set_can_be_fragmented(&self, value: bool);
 
-    /// Borrows the PrivateStyleData without checks.
+    /// Borrows the style data immutably. Fails on a conflicting borrow.
     #[inline(always)]
-    unsafe fn borrow_data_unchecked(&self) -> Option<*const PrivateStyleData>;
+    fn borrow_data(&self) -> Option<AtomicRef<PersistentStyleData>>;
 
-    /// Borrows the PrivateStyleData immutably. Fails on a conflicting borrow.
+    /// Borrows the style data mutably. Fails on a conflicting borrow.
     #[inline(always)]
-    fn borrow_data(&self) -> Option<Ref<PrivateStyleData>>;
+    fn mutate_data(&self) -> Option<AtomicRefMut<PersistentStyleData>>;
-
-    /// Borrows the PrivateStyleData mutably. Fails on a conflicting borrow.
-    #[inline(always)]
-    fn mutate_data(&self) -> Option<RefMut<PrivateStyleData>>;
 
     /// Get the description of how to account for recent style changes.
     fn restyle_damage(self) -> Self::ConcreteRestyleDamage;
@@ -167,13 +162,6 @@ pub trait TNode : Sized + Copy + Clone + NodeInfo {
 
     fn next_sibling(&self) -> Option<Self>;
 
-
-    /// Returns the style results for the given node. If CSS selector matching
-    /// has not yet been performed, fails.
-    fn style(&self, _context: &SharedStyleContext) -> Ref<Arc<ComputedValues>> {
-        Ref::map(self.borrow_data().unwrap(), |data| data.style.as_ref().unwrap())
-    }
-
     /// Removes the style from this node.
     fn unstyle(self) {
         self.mutate_data().unwrap().style = None;

components/style/gecko/wrapper.rs

@@ -5,7 +5,8 @@
 #![allow(unsafe_code)]
 
 
-use data::PrivateStyleData;
+use atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
+use data::PersistentStyleData;
 use dom::{LayoutIterator, NodeInfo, TDocument, TElement, TNode, TRestyleDamage, UnsafeNode};
 use dom::{OpaqueNode, PresentationalHintsSynthetizer};
 use element_state::ElementState;
@@ -34,7 +35,6 @@ use libc::uintptr_t;
 use parser::ParserContextExtraData;
 use properties::{ComputedValues, parse_style_attribute};
 use properties::PropertyDeclarationBlock;
-use refcell::{Ref, RefCell, RefMut};
 use selector_impl::ElementExt;
 use selector_matching::ApplicableDeclarationBlock;
 use selectors::Element;
@@ -48,11 +48,11 @@ use std::sync::atomic::{AtomicBool, AtomicPtr};
 use string_cache::{Atom, Namespace, WeakAtom, WeakNamespace};
 use url::Url;
 
-pub struct NonOpaqueStyleData(RefCell<PrivateStyleData>);
+pub struct NonOpaqueStyleData(AtomicRefCell<PersistentStyleData>);
 
 impl NonOpaqueStyleData {
     pub fn new() -> Self {
-        NonOpaqueStyleData(RefCell::new(PrivateStyleData::new()))
+        NonOpaqueStyleData(AtomicRefCell::new(PersistentStyleData::new()))
     }
 }
 
@@ -302,18 +302,12 @@ impl<'ln> TNode for GeckoNode<'ln> {
     }
 
     #[inline(always)]
-    unsafe fn borrow_data_unchecked(&self) -> Option<*const PrivateStyleData> {
+    fn borrow_data(&self) -> Option<AtomicRef<PersistentStyleData>> {
-        self.get_node_data().as_ref().map(|d| d.0.as_unsafe_cell().get()
-                                                  as *const PrivateStyleData)
-    }
-
-    #[inline(always)]
-    fn borrow_data(&self) -> Option<Ref<PrivateStyleData>> {
         self.get_node_data().as_ref().map(|d| d.0.borrow())
     }
 
     #[inline(always)]
-    fn mutate_data(&self) -> Option<RefMut<PrivateStyleData>> {
+    fn mutate_data(&self) -> Option<AtomicRefMut<PersistentStyleData>> {
         self.get_node_data().as_ref().map(|d| d.0.borrow_mut())
     }
 

components/style/lib.rs

@@ -61,6 +61,7 @@ extern crate num_integer;
 extern crate num_traits;
 #[cfg(feature = "gecko")] extern crate num_cpus;
 extern crate ordered_float;
+extern crate parking_lot;
 extern crate quickersort;
 extern crate rand;
 extern crate rustc_serialize;
@@ -80,6 +81,7 @@ extern crate util;
 #[macro_use] pub mod string_cache;
 
 pub mod animation;
+pub mod atomic_refcell;
 pub mod attr;
 pub mod bezier;
 pub mod cache;

components/style/matching.rs

@@ -11,7 +11,7 @@ use arc_ptr_eq;
 use cache::{LRUCache, SimpleHashCache};
 use cascade_info::CascadeInfo;
 use context::{SharedStyleContext, StyleContext};
-use data::PrivateStyleData;
+use data::PersistentStyleData;
 use dom::{NodeInfo, TElement, TNode, TRestyleDamage, UnsafeNode};
 use properties::{ComputedValues, PropertyDeclarationBlock, cascade};
 use properties::longhands::display::computed_value as display;
@@ -874,19 +874,9 @@ pub trait MatchMethods : TNode {
                                     -> RestyleResult
         where Ctx: StyleContext<'a>
     {
-        // Get our parent's style. This must be unsafe so that we don't touch the parent's
+        // Get our parent's style.
-        // borrow flags.
+        let parent_node_data = parent.as_ref().and_then(|x| x.borrow_data());
-        //
+        let parent_style = parent_node_data.as_ref().map(|x| x.style.as_ref().unwrap());
-        // FIXME(pcwalton): Isolate this unsafety into the `wrapper` module to allow
-        // enforced safe, race-free access to the parent style.
-        let parent_style = match parent {
-            Some(parent_node) => {
-                let parent_style = (*parent_node.borrow_data_unchecked().unwrap()).style.as_ref().unwrap();
-                Some(parent_style)
-            }
-            None => None,
-        };
-
 
         // In the case we're styling a text node, we don't need to compute the
         // restyle damage, since it's a subset of the restyle damage of the
@@ -945,7 +935,7 @@ pub trait MatchMethods : TNode {
 
     fn compute_damage_and_cascade_pseudos<'a, Ctx>(&self,
                                                    final_style: Arc<ComputedValues>,
-                                                   data: &mut PrivateStyleData,
+                                                   data: &mut PersistentStyleData,
                                                    context: &Ctx,
                                                    applicable_declarations: &ApplicableDeclarations,
                                                    mut applicable_declarations_cache: &mut ApplicableDeclarationsCache)

components/style/parallel.rs

@@ -161,9 +161,7 @@ fn bottom_up_dom<N, C>(root: OpaqueNode,
             Some(parent) => parent,
         };
 
-        let parent_data = unsafe {
+        let parent_data = parent.borrow_data().unwrap();
-            &*parent.borrow_data_unchecked().unwrap()
-        };
 
         if parent_data
             .parallel

ports/cef/Cargo.lock

@@ -1599,6 +1599,32 @@ dependencies = [
  "shared_library 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "owning_ref"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "parking_lot"
+version = "0.3.3"
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+ "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
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+
 [[package]]
 name = "phf"
 version = "0.7.16"
@@ -2195,6 +2221,7 @@ dependencies = [
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@@ -2791,6 +2818,9 @@ dependencies = [
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ports/geckolib/Cargo.lock

@@ -244,6 +244,32 @@ dependencies = [
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 [[package]]
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 version = "0.7.16"
@@ -353,6 +379,7 @@ dependencies = [
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  "ordered-float 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "parking_lot 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)",
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@@ -524,6 +551,9 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
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