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diff --git a/gfx/wr/webrender/src/intern.rs b/gfx/wr/webrender/src/intern.rs
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+/* 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/. */
+
+//! The interning module provides a generic data structure
+//! interning container. It is similar in concept to a
+//! traditional string interning container, but it is
+//! specialized to the WR thread model.
+//!
+//! There is an Interner structure, that lives in the
+//! scene builder thread, and a DataStore structure
+//! that lives in the frame builder thread.
+//!
+//! Hashing, interning and handle creation is done by
+//! the interner structure during scene building.
+//!
+//! Delta changes for the interner are pushed during
+//! a transaction to the frame builder. The frame builder
+//! is then able to access the content of the interned
+//! handles quickly, via array indexing.
+//!
+//! Epoch tracking ensures that the garbage collection
+//! step which the interner uses to remove items is
+//! only invoked on items that the frame builder thread
+//! is no longer referencing.
+//!
+//! Items in the data store are stored in a traditional
+//! free-list structure, for content access and memory
+//! usage efficiency.
+//!
+//! The epoch is incremented each time a scene is
+//! built. The most recently used scene epoch is
+//! stored inside each handle. This is then used for
+//! cache invalidation.
+
+use crate::internal_types::FastHashMap;
+use malloc_size_of::MallocSizeOf;
+use std::fmt::Debug;
+use std::hash::Hash;
+use std::marker::PhantomData;
+use std::{ops, u64};
+use crate::util::VecHelper;
+use crate::profiler::TransactionProfile;
+
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+#[derive(Debug, Copy, Clone, MallocSizeOf, PartialEq)]
+struct Epoch(u32);
+
+/// A list of updates to be applied to the data store,
+/// provided by the interning structure.
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+#[derive(MallocSizeOf)]
+pub struct UpdateList<S> {
+    /// Items to insert.
+    pub insertions: Vec<Insertion<S>>,
+
+    /// Items to remove.
+    pub removals: Vec<Removal>,
+}
+
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+#[derive(MallocSizeOf)]
+pub struct Insertion<S> {
+    pub index: usize,
+    pub uid: ItemUid,
+    pub value: S,
+}
+
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+#[derive(MallocSizeOf)]
+pub struct Removal {
+    pub index: usize,
+    pub uid: ItemUid,
+}
+
+impl<S> UpdateList<S> {
+    fn new() -> UpdateList<S> {
+        UpdateList {
+            insertions: Vec::new(),
+            removals: Vec::new(),
+        }
+    }
+
+    fn take_and_preallocate(&mut self) -> UpdateList<S> {
+        UpdateList {
+            insertions: self.insertions.take_and_preallocate(),
+            removals: self.removals.take_and_preallocate(),
+        }
+    }
+}
+
+/// A globally, unique identifier
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+#[derive(Debug, Copy, Clone, Eq, Hash, MallocSizeOf, PartialEq)]
+pub struct ItemUid {
+    uid: u64,
+}
+
+impl ItemUid {
+    // Intended for debug usage only
+    pub fn get_uid(&self) -> u64 {
+        self.uid
+    }
+}
+
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+#[derive(Debug, MallocSizeOf, PartialEq)]
+pub struct Handle<I> {
+    index: u32,
+    epoch: Epoch,
+    _marker: PhantomData<I>,
+}
+
+impl<I> Clone for Handle<I> {
+    fn clone(&self) -> Self {
+        Handle {
+            index: self.index,
+            epoch: self.epoch,
+            _marker: self._marker,
+        }
+    }
+}
+
+impl<I> Copy for Handle<I> {}
+
+impl<I> Handle<I> {
+    pub fn uid(&self) -> ItemUid {
+        ItemUid {
+            // The index in the freelist + the epoch it was interned generates a stable
+            // unique id for an interned element.
+            uid: ((self.index as u64) << 32) | self.epoch.0 as u64
+        }
+    }
+}
+
+pub trait InternDebug {
+    fn on_interned(&self, _uid: ItemUid) {}
+}
+
+/// The data store lives in the frame builder thread. It
+/// contains a free-list of items for fast access.
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+#[derive(MallocSizeOf)]
+pub struct DataStore<I: Internable> {
+    items: Vec<Option<I::StoreData>>,
+}
+
+impl<I: Internable> Default for DataStore<I> {
+    fn default() -> Self {
+        DataStore {
+            items: Vec::new(),
+        }
+    }
+}
+
+impl<I: Internable> DataStore<I> {
+    /// Apply any updates from the scene builder thread to
+    /// this data store.
+    pub fn apply_updates(
+        &mut self,
+        update_list: UpdateList<I::Key>,
+        profile: &mut TransactionProfile,
+    ) {
+        for insertion in update_list.insertions {
+            self.items
+                .entry(insertion.index)
+                .set(Some(insertion.value.into()));
+        }
+
+        for removal in update_list.removals {
+            self.items[removal.index] = None;
+        }
+
+        profile.set(I::PROFILE_COUNTER, self.items.len());
+    }
+}
+
+/// Retrieve an item from the store via handle
+impl<I: Internable> ops::Index<Handle<I>> for DataStore<I> {
+    type Output = I::StoreData;
+    fn index(&self, handle: Handle<I>) -> &I::StoreData {
+        self.items[handle.index as usize].as_ref().expect("Bad datastore lookup")
+    }
+}
+
+/// Retrieve a mutable item from the store via handle
+/// Retrieve an item from the store via handle
+impl<I: Internable> ops::IndexMut<Handle<I>> for DataStore<I> {
+    fn index_mut(&mut self, handle: Handle<I>) -> &mut I::StoreData {
+        self.items[handle.index as usize].as_mut().expect("Bad datastore lookup")
+    }
+}
+
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+#[derive(MallocSizeOf)]
+struct ItemDetails<I> {
+    /// Frame that this element was first interned
+    interned_epoch: Epoch,
+    /// Last frame this element was referenced (used to GC intern items)
+    last_used_epoch: Epoch,
+    /// Index into the freelist this item is located
+    index: usize,
+    /// Type marker for create_handle method
+    _marker: PhantomData<I>,
+}
+
+impl<I> ItemDetails<I> {
+    /// Construct a stable handle value from the item details
+    fn create_handle(&self) -> Handle<I> {
+        Handle {
+            index: self.index as u32,
+            epoch: self.interned_epoch,
+            _marker: PhantomData,
+        }
+    }
+}
+
+/// The main interning data structure. This lives in the
+/// scene builder thread, and handles hashing and interning
+/// unique data structures. It also manages a free-list for
+/// the items in the data store, which is synchronized via
+/// an update list of additions / removals.
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+#[derive(MallocSizeOf)]
+pub struct Interner<I: Internable> {
+    /// Uniquely map an interning key to a handle
+    map: FastHashMap<I::Key, ItemDetails<I>>,
+    /// List of free slots in the data store for re-use.
+    free_list: Vec<usize>,
+    /// Pending list of updates that need to be applied.
+    update_list: UpdateList<I::Key>,
+    /// The current epoch for the interner.
+    current_epoch: Epoch,
+    /// The information associated with each interned
+    /// item that can be accessed by the interner.
+    local_data: Vec<I::InternData>,
+}
+
+impl<I: Internable> Default for Interner<I> {
+    fn default() -> Self {
+        Interner {
+            map: FastHashMap::default(),
+            free_list: Vec::new(),
+            update_list: UpdateList::new(),
+            current_epoch: Epoch(1),
+            local_data: Vec::new(),
+        }
+    }
+}
+
+impl<I: Internable> Interner<I> {
+    /// Intern a data structure, and return a handle to
+    /// that data. The handle can then be stored in the
+    /// frame builder, and safely accessed via the data
+    /// store that lives in the frame builder thread.
+    /// The provided closure is invoked to build the
+    /// local data about an interned structure if the
+    /// key isn't already interned.
+    pub fn intern<F>(
+        &mut self,
+        data: &I::Key,
+        fun: F,
+    ) -> Handle<I> where F: FnOnce() -> I::InternData {
+        // Use get_mut rather than entry here to avoid
+        // cloning the (sometimes large) key in the common
+        // case, where the data already exists in the interner.
+        if let Some(details) = self.map.get_mut(data) {
+            // Update the last referenced frame for this element
+            details.last_used_epoch = self.current_epoch;
+            // Return a stable handle value for dependency checking
+            return details.create_handle();
+        }
+
+        // We need to intern a new data item. First, find out
+        // if there is a spare slot in the free-list that we
+        // can use. Otherwise, append to the end of the list.
+        let index = match self.free_list.pop() {
+            Some(index) => index,
+            None => self.local_data.len(),
+        };
+
+        // Generate a handle for access via the data store.
+        let handle = Handle {
+            index: index as u32,
+            epoch: self.current_epoch,
+            _marker: PhantomData,
+        };
+
+        let uid = handle.uid();
+
+        // Add a pending update to insert the new data.
+        self.update_list.insertions.push(Insertion {
+            index,
+            uid,
+            value: data.clone(),
+        });
+
+        #[cfg(debug_assertions)]
+        data.on_interned(uid);
+
+        // Store this handle so the next time it is
+        // interned, it gets re-used.
+        self.map.insert(data.clone(), ItemDetails {
+            interned_epoch: self.current_epoch,
+            last_used_epoch: self.current_epoch,
+            index,
+            _marker: PhantomData,
+        });
+
+        // Create the local data for this item that is
+        // being interned.
+        self.local_data.entry(index).set(fun());
+
+        handle
+    }
+
+    /// Retrieve the pending list of updates for an interner
+    /// that need to be applied to the data store. Also run
+    /// a GC step that removes old entries.
+    pub fn end_frame_and_get_pending_updates(&mut self) -> UpdateList<I::Key> {
+        let mut update_list = self.update_list.take_and_preallocate();
+
+        let free_list = &mut self.free_list;
+        let current_epoch = self.current_epoch.0;
+
+        // First, run a GC step. Walk through the handles, and
+        // if we find any that haven't been used for some time,
+        // remove them. If this ever shows up in profiles, we
+        // can make the GC step partial (scan only part of the
+        // map each frame). It also might make sense in the
+        // future to adjust how long items remain in the cache
+        // based on the current size of the list.
+        self.map.retain(|_, details| {
+            if details.last_used_epoch.0 + 10 < current_epoch {
+                // To expire an item:
+                //  - Add index to the free-list for re-use.
+                //  - Add an update to the data store to invalidate this slot.
+                //  - Remove from the hash map.
+                free_list.push(details.index);
+                update_list.removals.push(Removal {
+                    index: details.index,
+                    uid: details.create_handle().uid(),
+                });
+                return false;
+            }
+
+            true
+        });
+
+        // Begin the next epoch
+        self.current_epoch = Epoch(self.current_epoch.0 + 1);
+
+        update_list
+    }
+}
+
+/// Retrieve the local data for an item from the interner via handle
+impl<I: Internable> ops::Index<Handle<I>> for Interner<I> {
+    type Output = I::InternData;
+    fn index(&self, handle: Handle<I>) -> &I::InternData {
+        &self.local_data[handle.index as usize]
+    }
+}
+
+/// Meta-macro to enumerate the various interner identifiers and types.
+///
+/// IMPORTANT: Keep this synchronized with the list in mozilla-central located at
+/// gfx/webrender_bindings/webrender_ffi.h
+///
+/// Note that this could be a lot less verbose if concat_idents! were stable. :-(
+#[macro_export]
+macro_rules! enumerate_interners {
+    ($macro_name: ident) => {
+        $macro_name! {
+            clip: ClipIntern,
+            prim: PrimitiveKeyKind,
+            normal_border: NormalBorderPrim,
+            image_border: ImageBorder,
+            image: Image,
+            yuv_image: YuvImage,
+            line_decoration: LineDecoration,
+            linear_grad: LinearGradient,
+            radial_grad: RadialGradient,
+            conic_grad: ConicGradient,
+            picture: Picture,
+            text_run: TextRun,
+            filter_data: FilterDataIntern,
+            backdrop: Backdrop,
+        }
+    }
+}
+
+macro_rules! declare_interning_memory_report {
+    ( $( $name:ident: $ty:ident, )+ ) => {
+        ///
+        #[repr(C)]
+        #[derive(AddAssign, Clone, Debug, Default)]
+        pub struct InternerSubReport {
+            $(
+                ///
+                pub $name: usize,
+            )+
+        }
+    }
+}
+
+enumerate_interners!(declare_interning_memory_report);
+
+/// Memory report for interning-related data structures.
+/// cbindgen:derive-eq=false
+/// cbindgen:derive-ostream=false
+#[repr(C)]
+#[derive(Clone, Debug, Default)]
+pub struct InterningMemoryReport {
+    ///
+    pub interners: InternerSubReport,
+    ///
+    pub data_stores: InternerSubReport,
+}
+
+impl ::std::ops::AddAssign for InterningMemoryReport {
+    fn add_assign(&mut self, other: InterningMemoryReport) {
+        self.interners += other.interners;
+        self.data_stores += other.data_stores;
+    }
+}
+
+// The trick to make trait bounds configurable by features.
+mod dummy {
+    #[cfg(not(feature = "capture"))]
+    pub trait Serialize {}
+    #[cfg(not(feature = "capture"))]
+    impl<T> Serialize for T {}
+    #[cfg(not(feature = "replay"))]
+    pub trait Deserialize<'a> {}
+    #[cfg(not(feature = "replay"))]
+    impl<'a, T> Deserialize<'a> for T {}
+}
+#[cfg(feature = "capture")]
+use serde::Serialize as InternSerialize;
+#[cfg(not(feature = "capture"))]
+use self::dummy::Serialize as InternSerialize;
+#[cfg(feature = "replay")]
+use serde::Deserialize as InternDeserialize;
+#[cfg(not(feature = "replay"))]
+use self::dummy::Deserialize as InternDeserialize;
+
+/// Implement `Internable` for a type that wants to participate in interning.
+pub trait Internable: MallocSizeOf {
+    type Key: Eq + Hash + Clone + Debug + MallocSizeOf + InternDebug + InternSerialize + for<'a> InternDeserialize<'a>;
+    type StoreData: From<Self::Key> + MallocSizeOf + InternSerialize + for<'a> InternDeserialize<'a>;
+    type InternData: MallocSizeOf + InternSerialize + for<'a> InternDeserialize<'a>;
+
+    // Profile counter indices, see the list in profiler.rs
+    const PROFILE_COUNTER: usize;
+}