Auto merge of #14835 - bholley:external_atomic_refcell, r=Manishearth

Switch to crates.io for atomic_refcell

r? @Manishearth

See #14828 for backstory.

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components/layout/Cargo.toml

@@ -11,6 +11,7 @@ path = "lib.rs"
 
 [dependencies]
 app_units = "0.3"
+atomic_refcell = "0.1"
 bitflags = "0.7"
 canvas_traits = {path = "../canvas_traits"}
 cssparser = {version = "0.7", features = ["heap_size", "serde-serialization"]}

components/layout/lib.rs

@@ -16,6 +16,7 @@
 #![plugin(plugins)]
 
 extern crate app_units;
+extern crate atomic_refcell;
 #[allow(unused_extern_crates)]
 #[macro_use]
 extern crate bitflags;

components/layout/traversal.rs

@@ -4,6 +4,7 @@
 
 //! Traversals over the DOM and flow trees, running the layout computations.
 
+use atomic_refcell::AtomicRefCell;
 use construct::FlowConstructor;
 use context::{LayoutContext, ScopedThreadLocalLayoutContext, SharedLayoutContext};
 use display_list_builder::DisplayListBuildState;
@@ -11,7 +12,6 @@ use flow::{self, PreorderFlowTraversal};
 use flow::{CAN_BE_FRAGMENTED, Flow, ImmutableFlowUtils, PostorderFlowTraversal};
 use script_layout_interface::wrapper_traits::{LayoutNode, ThreadSafeLayoutNode};
 use servo_config::opts;
-use style::atomic_refcell::AtomicRefCell;
 use style::context::{SharedStyleContext, StyleContext};
 use style::data::ElementData;
 use style::dom::{TElement, TNode};

components/layout/wrapper.rs

@@ -30,12 +30,12 @@
 
 #![allow(unsafe_code)]
 
+use atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
 use core::nonzero::NonZero;
 use data::{LayoutDataFlags, PersistentLayoutData};
 use script_layout_interface::{OpaqueStyleAndLayoutData, PartialPersistentLayoutData};
 use script_layout_interface::wrapper_traits::{LayoutNode, ThreadSafeLayoutElement, ThreadSafeLayoutNode};
 use script_layout_interface::wrapper_traits::GetLayoutData;
-use style::atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
 use style::computed_values::content::{self, ContentItem};
 
 pub type NonOpaqueStyleAndLayoutData = AtomicRefCell<PersistentLayoutData>;

components/script/Cargo.toml

@@ -24,6 +24,7 @@ tinyfiledialogs = {git = "https://github.com/jdm/tinyfiledialogs"}
 angle = {git = "https://github.com/servo/angle", branch = "servo"}
 app_units = "0.3"
 audio-video-metadata = "0.1.2"
+atomic_refcell = "0.1"
 bitflags = "0.7"
 bluetooth_traits = {path = "../bluetooth_traits"}
 canvas_traits = {path = "../canvas_traits"}

components/script/layout_wrapper.rs

@@ -30,6 +30,7 @@
 
 #![allow(unsafe_code)]
 
+use atomic_refcell::AtomicRefCell;
 use dom::bindings::inheritance::{CharacterDataTypeId, ElementTypeId};
 use dom::bindings::inheritance::{HTMLElementTypeId, NodeTypeId};
 use dom::bindings::js::LayoutJS;
@@ -58,7 +59,6 @@ use std::marker::PhantomData;
 use std::mem::transmute;
 use std::sync::Arc;
 use std::sync::atomic::Ordering;
-use style::atomic_refcell::AtomicRefCell;
 use style::attr::AttrValue;
 use style::computed_values::display;
 use style::context::{QuirksMode, SharedStyleContext};

components/script/lib.rs

@@ -28,6 +28,7 @@
 
 extern crate angle;
 extern crate app_units;
+extern crate atomic_refcell;
 extern crate audio_video_metadata;
 #[allow(unused_extern_crates)]
 #[macro_use]

components/script_layout_interface/Cargo.toml

@@ -11,6 +11,7 @@ path = "lib.rs"
 
 [dependencies]
 app_units = "0.3"
+atomic_refcell = "0.1"
 bitflags = "0.7"
 canvas_traits = {path = "../canvas_traits"}
 cssparser = {version = "0.7", features = ["heap_size", "serde-serialization"]}

components/script_layout_interface/lib.rs

@@ -14,6 +14,7 @@
 #![plugin(plugins)]
 
 extern crate app_units;
+extern crate atomic_refcell;
 #[allow(unused_extern_crates)]
 #[macro_use]
 extern crate bitflags;
@@ -44,12 +45,12 @@ pub mod reporter;
 pub mod rpc;
 pub mod wrapper_traits;
 
+use atomic_refcell::AtomicRefCell;
 use canvas_traits::CanvasMsg;
 use core::nonzero::NonZero;
 use ipc_channel::ipc::IpcSender;
 use libc::c_void;
 use std::sync::atomic::AtomicIsize;
-use style::atomic_refcell::AtomicRefCell;
 use style::data::ElementData;
 
 pub struct PartialPersistentLayoutData {

components/script_layout_interface/wrapper_traits.rs

@@ -8,6 +8,7 @@ use HTMLCanvasData;
 use LayoutNodeType;
 use OpaqueStyleAndLayoutData;
 use SVGSVGData;
+use atomic_refcell::AtomicRefCell;
 use gfx_traits::{ByteIndex, FragmentType, ScrollRootId};
 use html5ever_atoms::{Namespace, LocalName};
 use msg::constellation_msg::PipelineId;
@@ -15,7 +16,6 @@ use range::Range;
 use servo_url::ServoUrl;
 use std::fmt::Debug;
 use std::sync::Arc;
-use style::atomic_refcell::AtomicRefCell;
 use style::computed_values::display;
 use style::context::SharedStyleContext;
 use style::data::ElementData;

components/style/Cargo.toml

@@ -23,6 +23,7 @@ testing = []
 
 [dependencies]
 app_units = "0.3"
+atomic_refcell = "0.1"
 bitflags = "0.7"
 cfg-if = "0.1.0"
 cssparser = "0.7"

components/style/atomic_refcell.rs

@@ -1,346 +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/. */
-
-//! Implements a 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 is
-//! overkill, and has key disadvantages:
-//! * Performance: Even the fastest existing implementation of RwLock (that of
-//!   parking_lot) performs at least two atomic operations during immutable
-//!   borrows. This makes mutable borrows significantly cheaper than immutable
-//!   borrows, leading to weird incentives when writing performance-critical
-//!   code.
-//! * Features: Implementing AtomicRefCell on top of RwLock makes it impossible
-//!   to implement useful things like AtomicRef{,Mut}::map.
-//!
-//! As such, we re-implement RefCell semantics from scratch with a single atomic
-//! reference count. The primary complication of this scheme relates to keeping
-//! things in a consistent state when one thread performs an illegal borrow and
-//! panics. Since an AtomicRefCell can be accessed by multiple threads, and since
-//! panics are recoverable, we need to ensure that an illegal (panicking) access by
-//! one thread does not lead to undefined behavior on other, still-running threads.
-//!
-//! So we represent things as follows:
-//! * Any value with the high bit set (so half the total refcount space) indicates
-//!   a mutable borrow.
-//! * Mutable borrows perform an atomic compare-and-swap, swapping in the high bit
-//!   if the current value is zero. If the current value is non-zero, the thread
-//!   panics and the value is left undisturbed.
-//! * Immutable borrows perform an atomic increment. If the new value has the high
-//!   bit set, the thread panics. The incremented refcount is left as-is, since it
-//!   still represents a valid mutable borrow. When the mutable borrow is released,
-//!   the refcount is set unconditionally to zero, clearing any stray increments by
-//!   panicked threads.
-//!
-//! There are a few additional purely-academic complications to handle overflow,
-//! which are documented in the implementation.
-//!
-//! The rest of this module is mostly derived by copy-pasting the implementation of
-//! RefCell and fixing things up as appropriate. Certain non-threadsafe methods
-//! have been removed. We segment the concurrency logic from the rest of the code to
-//! keep the tricky parts small and easy to audit.
-
-#![allow(unsafe_code)]
-#![deny(missing_docs)]
-
-use std::cell::UnsafeCell;
-use std::cmp;
-use std::fmt;
-use std::fmt::Debug;
-use std::ops::{Deref, DerefMut};
-use std::sync::atomic;
-use std::sync::atomic::AtomicUsize;
-
-/// A threadsafe analogue to RefCell.
-pub struct AtomicRefCell<T: ?Sized> {
-    borrow: AtomicUsize,
-    value: UnsafeCell<T>,
-}
-
-impl<T> AtomicRefCell<T> {
-    /// Creates a new `AtomicRefCell` containing `value`.
-    #[inline]
-    pub fn new(value: T) -> AtomicRefCell<T> {
-        AtomicRefCell {
-            borrow: AtomicUsize::new(0),
-            value: UnsafeCell::new(value),
-        }
-    }
-
-    /// Consumes the `AtomicRefCell`, returning the wrapped value.
-    #[inline]
-    pub fn into_inner(self) -> T {
-        debug_assert!(self.borrow.load(atomic::Ordering::Acquire) == 0);
-        unsafe { self.value.into_inner() }
-    }
-}
-
-impl<T: ?Sized> AtomicRefCell<T> {
-    /// Immutably borrows the wrapped value.
-    #[inline]
-    pub fn borrow(&self) -> AtomicRef<T> {
-        AtomicRef {
-            value: unsafe { &*self.value.get() },
-            borrow: AtomicBorrowRef::new(&self.borrow),
-        }
-    }
-
-    /// Mutably borrows the wrapped value.
-    #[inline]
-    pub fn borrow_mut(&self) -> AtomicRefMut<T> {
-        AtomicRefMut {
-            value: unsafe { &mut *self.value.get() },
-            borrow: AtomicBorrowRefMut::new(&self.borrow),
-        }
-    }
-
-    /// Returns a raw pointer to the underlying data in this cell.
-    ///
-    /// External synchronization is needed to avoid data races when dereferencing
-    /// the pointer.
-    #[inline]
-    pub fn as_ptr(&self) -> *mut T {
-        self.value.get()
-    }
-}
-
-//
-// Core synchronization logic. Keep this section small and easy to audit.
-//
-
-const HIGH_BIT: usize = !(::std::usize::MAX >> 1);
-const MAX_FAILED_BORROWS: usize = HIGH_BIT + (HIGH_BIT >> 1);
-
-struct AtomicBorrowRef<'b> {
-    borrow: &'b AtomicUsize,
-}
-
-impl<'b> AtomicBorrowRef<'b> {
-    #[inline]
-    fn new(borrow: &'b AtomicUsize) -> Self {
-        let new = borrow.fetch_add(1, atomic::Ordering::Acquire) + 1;
-
-        // If the new count has the high bit set, panic. The specifics of how
-        // we panic is interesting for soundness, but irrelevant for real programs.
-        //
-        // FIXME(bholley): Counter-intuitively, moving the panic logic below out-of-
-        // line costs about 2ns on the benchmark. My best guess is that we end up
-        // predicting the wrong branch, but there's no way to mark something as
-        // unlikely on stable rust. :-(
-        if new & HIGH_BIT != 0 {
-            if new == HIGH_BIT {
-                // We overflowed into the reserved upper half of the refcount
-                // space. Before panicking, decrement the refcount to leave things
-                // in a consistent immutable-borrow state.
-                //
-                // This can basically only happen if somebody forget()s AtomicRefs
-                // in a tight loop.
-                borrow.fetch_sub(1, atomic::Ordering::Release);
-                panic!("too many immutable borrows");
-            } else if new >= MAX_FAILED_BORROWS {
-                // During the mutable borrow, an absurd number of threads have
-                // incremented the refcount and panicked. To avoid hypothetically
-                // wrapping the refcount, we abort the process once a certain
-                // threshold is reached.
-                //
-                // This requires billions of threads to have panicked already, and
-                // so will never happen in a real program.
-                println!("Too many failed borrows");
-                ::std::process::exit(1);
-            } else {
-                // This is the normal case, and the only one which should happen
-                // in a real program.
-                panic!("already mutably borrowed");
-            }
-        }
-
-        AtomicBorrowRef { borrow: borrow }
-    }
-}
-
-impl<'b> Drop for AtomicBorrowRef<'b> {
-    #[inline]
-    fn drop(&mut self) {
-        let old = self.borrow.fetch_sub(1, atomic::Ordering::Release);
-        // This assertion is technically incorrect in the case where another
-        // thread hits the hypothetical overflow case, since we might observe
-        // the refcount before it fixes it up (and panics). But that never will
-        // never happen in a real program, and this is a debug_assert! anyway.
-        debug_assert!(old & HIGH_BIT == 0);
-    }
-}
-
-struct AtomicBorrowRefMut<'b> {
-    borrow: &'b AtomicUsize,
-}
-
-impl<'b> Drop for AtomicBorrowRefMut<'b> {
-    #[inline]
-    fn drop(&mut self) {
-        self.borrow.store(0, atomic::Ordering::Release);
-    }
-}
-
-impl<'b> AtomicBorrowRefMut<'b> {
-    #[inline]
-    fn new(borrow: &'b AtomicUsize) -> AtomicBorrowRefMut<'b> {
-        // Use compare-and-swap to avoid corrupting the immutable borrow count
-        // on illegal mutable borrows.
-        let old = match borrow.compare_exchange(0, HIGH_BIT, atomic::Ordering::Acquire, atomic::Ordering::Relaxed) {
-            Ok(x) => x,
-            Err(x) => x,
-        };
-        assert!(old == 0, "already {} borrowed", if old & HIGH_BIT == 0 { "immutably" } else { "mutably" });
-        AtomicBorrowRefMut {
-            borrow: borrow
-        }
-    }
-}
-
-unsafe impl<T: ?Sized + Send + Sync> Send for AtomicRefCell<T> {}
-unsafe impl<T: ?Sized + Send + Sync> Sync for AtomicRefCell<T> {}
-
-//
-// End of core synchronization logic. No tricky thread stuff allowed below
-// this point.
-//
-
-impl<T: Clone> Clone for AtomicRefCell<T> {
-    #[inline]
-    fn clone(&self) -> AtomicRefCell<T> {
-        AtomicRefCell::new(self.borrow().clone())
-    }
-}
-
-impl<T: Default> Default for AtomicRefCell<T> {
-    #[inline]
-    fn default() -> AtomicRefCell<T> {
-        AtomicRefCell::new(Default::default())
-    }
-}
-
-impl<T: ?Sized + PartialEq> PartialEq for AtomicRefCell<T> {
-    #[inline]
-    fn eq(&self, other: &AtomicRefCell<T>) -> bool {
-        *self.borrow() == *other.borrow()
-    }
-}
-
-impl<T: ?Sized + Eq> Eq for AtomicRefCell<T> {}
-
-impl<T: ?Sized + PartialOrd> PartialOrd for AtomicRefCell<T> {
-    #[inline]
-    fn partial_cmp(&self, other: &AtomicRefCell<T>) -> Option<cmp::Ordering> {
-        self.borrow().partial_cmp(&*other.borrow())
-    }
-}
-
-impl<T: ?Sized + Ord> Ord for AtomicRefCell<T> {
-    #[inline]
-    fn cmp(&self, other: &AtomicRefCell<T>) -> cmp::Ordering {
-        self.borrow().cmp(&*other.borrow())
-    }
-}
-
-impl<T> From<T> for AtomicRefCell<T> {
-    fn from(t: T) -> AtomicRefCell<T> {
-        AtomicRefCell::new(t)
-    }
-}
-
-impl<'b> Clone for AtomicBorrowRef<'b> {
-    #[inline]
-    fn clone(&self) -> AtomicBorrowRef<'b> {
-        AtomicBorrowRef::new(self.borrow)
-    }
-}
-
-/// A wrapper type for an immutably borrowed value from an `AtomicRefCell<T>`.
-pub struct AtomicRef<'b, T: ?Sized + 'b> {
-    value: &'b T,
-    borrow: AtomicBorrowRef<'b>,
-}
-
-
-impl<'b, T: ?Sized> Deref for AtomicRef<'b, T> {
-    type Target = T;
-
-    #[inline]
-    fn deref(&self) -> &T {
-        self.value
-    }
-}
-
-impl<'b, T: ?Sized> AtomicRef<'b, T> {
-    /// Copies an `AtomicRef`.
-    #[inline]
-    pub fn clone(orig: &AtomicRef<'b, T>) -> AtomicRef<'b, T> {
-        AtomicRef {
-            value: orig.value,
-            borrow: orig.borrow.clone(),
-        }
-    }
-
-    /// Make a new `AtomicRef` for a component of the borrowed data.
-    #[inline]
-    pub fn map<U: ?Sized, F>(orig: AtomicRef<'b, T>, f: F) -> AtomicRef<'b, U>
-        where F: FnOnce(&T) -> &U
-    {
-        AtomicRef {
-            value: f(orig.value),
-            borrow: orig.borrow,
-        }
-    }
-}
-
-impl<'b, T: ?Sized> AtomicRefMut<'b, T> {
-    /// Make a new `AtomicRefMut` for a component of the borrowed data, e.g. an enum
-    /// variant.
-    #[inline]
-    pub fn map<U: ?Sized, F>(orig: AtomicRefMut<'b, T>, f: F) -> AtomicRefMut<'b, U>
-        where F: FnOnce(&mut T) -> &mut U
-    {
-        AtomicRefMut {
-            value: f(orig.value),
-            borrow: orig.borrow,
-        }
-    }
-}
-
-/// A wrapper type for a mutably borrowed value from an `AtomicRefCell<T>`.
-pub struct AtomicRefMut<'b, T: ?Sized + 'b> {
-    value: &'b mut T,
-    borrow: AtomicBorrowRefMut<'b>,
-}
-
-impl<'b, T: ?Sized> Deref for AtomicRefMut<'b, T> {
-    type Target = T;
-
-    #[inline]
-    fn deref(&self) -> &T {
-        self.value
-    }
-}
-
-impl<'b, T: ?Sized> DerefMut for AtomicRefMut<'b, T> {
-    #[inline]
-    fn deref_mut(&mut self) -> &mut T {
-        self.value
-    }
-}
-
-impl<'b, T: ?Sized + Debug + 'b> Debug for AtomicRef<'b, T> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        self.value.fmt(f)
-     }
-}
-
-impl<'b, T: ?Sized + Debug + 'b> Debug for AtomicRefMut<'b, T> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        self.value.fmt(f)
-    }
-}

components/style/lib.rs

@@ -40,6 +40,7 @@
 #![recursion_limit = "500"]  // For define_css_keyword_enum! in -moz-appearance
 
 extern crate app_units;
+extern crate atomic_refcell;
 #[allow(unused_extern_crates)]
 #[macro_use]
 extern crate bitflags;
@@ -89,7 +90,6 @@ extern crate time;
 extern crate unicode_segmentation;
 
 pub mod animation;
-pub mod atomic_refcell;
 #[allow(missing_docs)] // TODO.
 pub mod attr;
 pub mod bezier;