1 /* This Source Code Form is subject to the terms of the Mozilla Public
2 * License, v. 2.0. If a copy of the MPL was not distributed with this
3 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
5 //! The interning module provides a generic data structure
6 //! interning container. It is similar in concept to a
7 //! traditional string interning container, but it is
8 //! specialized to the WR thread model.
10 //! There is an Interner structure, that lives in the
11 //! scene builder thread, and a DataStore structure
12 //! that lives in the frame builder thread.
14 //! Hashing, interning and handle creation is done by
15 //! the interner structure during scene building.
17 //! Delta changes for the interner are pushed during
18 //! a transaction to the frame builder. The frame builder
19 //! is then able to access the content of the interned
20 //! handles quickly, via array indexing.
22 //! Epoch tracking ensures that the garbage collection
23 //! step which the interner uses to remove items is
24 //! only invoked on items that the frame builder thread
25 //! is no longer referencing.
27 //! Items in the data store are stored in a traditional
28 //! free-list structure, for content access and memory
31 //! The epoch is incremented each time a scene is
32 //! built. The most recently used scene epoch is
33 //! stored inside each handle. This is then used for
34 //! cache invalidation.
36 use crate::internal_types::FastHashMap;
37 use malloc_size_of::MallocSizeOf;
40 use std::marker::PhantomData;
42 use crate::util::VecHelper;
43 use crate::profiler::TransactionProfile;
45 #[cfg_attr(feature = "capture", derive(Serialize))]
46 #[cfg_attr(feature = "replay", derive(Deserialize))]
47 #[derive(Debug, Copy, Clone, Hash, MallocSizeOf, PartialEq, Eq)]
50 /// A list of updates to be applied to the data store,
51 /// provided by the interning structure.
52 #[cfg_attr(feature = "capture", derive(Serialize))]
53 #[cfg_attr(feature = "replay", derive(Deserialize))]
54 #[derive(MallocSizeOf)]
55 pub struct UpdateList<S> {
57 pub insertions: Vec<Insertion<S>>,
60 pub removals: Vec<Removal>,
63 #[cfg_attr(feature = "capture", derive(Serialize))]
64 #[cfg_attr(feature = "replay", derive(Deserialize))]
65 #[derive(MallocSizeOf)]
66 pub struct Insertion<S> {
72 #[cfg_attr(feature = "capture", derive(Serialize))]
73 #[cfg_attr(feature = "replay", derive(Deserialize))]
74 #[derive(MallocSizeOf)]
80 impl<S> UpdateList<S> {
81 fn new() -> UpdateList<S> {
83 insertions: Vec::new(),
88 fn take_and_preallocate(&mut self) -> UpdateList<S> {
90 insertions: self.insertions.take_and_preallocate(),
91 removals: self.removals.take_and_preallocate(),
96 /// A globally, unique identifier
97 #[cfg_attr(feature = "capture", derive(Serialize))]
98 #[cfg_attr(feature = "replay", derive(Deserialize))]
99 #[derive(Debug, Copy, Clone, Eq, Hash, MallocSizeOf, PartialEq)]
105 // Intended for debug usage only
106 pub fn get_uid(&self) -> u64 {
111 #[cfg_attr(feature = "capture", derive(Serialize))]
112 #[cfg_attr(feature = "replay", derive(Deserialize))]
113 #[derive(Debug, Hash, MallocSizeOf, PartialEq, Eq)]
114 pub struct Handle<I> {
117 _marker: PhantomData<I>,
120 impl<I> Clone for Handle<I> {
121 fn clone(&self) -> Self {
125 _marker: self._marker,
130 impl<I> Copy for Handle<I> {}
133 pub fn uid(&self) -> ItemUid {
135 // The index in the freelist + the epoch it was interned generates a stable
136 // unique id for an interned element.
137 uid: ((self.index as u64) << 32) | self.epoch.0 as u64
142 pub trait InternDebug {
143 fn on_interned(&self, _uid: ItemUid) {}
146 /// The data store lives in the frame builder thread. It
147 /// contains a free-list of items for fast access.
148 #[cfg_attr(feature = "capture", derive(Serialize))]
149 #[cfg_attr(feature = "replay", derive(Deserialize))]
150 #[derive(MallocSizeOf)]
151 pub struct DataStore<I: Internable> {
152 items: Vec<Option<I::StoreData>>,
155 impl<I: Internable> Default for DataStore<I> {
156 fn default() -> Self {
163 impl<I: Internable> DataStore<I> {
164 /// Apply any updates from the scene builder thread to
166 pub fn apply_updates(
168 update_list: UpdateList<I::Key>,
169 profile: &mut TransactionProfile,
171 for insertion in update_list.insertions {
173 .entry(insertion.index)
174 .set(Some(insertion.value.into()));
177 for removal in update_list.removals {
178 self.items[removal.index] = None;
181 profile.set(I::PROFILE_COUNTER, self.items.len());
185 /// Retrieve an item from the store via handle
186 impl<I: Internable> ops::Index<Handle<I>> for DataStore<I> {
187 type Output = I::StoreData;
188 fn index(&self, handle: Handle<I>) -> &I::StoreData {
189 self.items[handle.index as usize].as_ref().expect("Bad datastore lookup")
193 /// Retrieve a mutable item from the store via handle
194 /// Retrieve an item from the store via handle
195 impl<I: Internable> ops::IndexMut<Handle<I>> for DataStore<I> {
196 fn index_mut(&mut self, handle: Handle<I>) -> &mut I::StoreData {
197 self.items[handle.index as usize].as_mut().expect("Bad datastore lookup")
201 #[cfg_attr(feature = "capture", derive(Serialize))]
202 #[cfg_attr(feature = "replay", derive(Deserialize))]
203 #[derive(MallocSizeOf)]
204 struct ItemDetails<I> {
205 /// Frame that this element was first interned
206 interned_epoch: Epoch,
207 /// Last frame this element was referenced (used to GC intern items)
208 last_used_epoch: Epoch,
209 /// Index into the freelist this item is located
211 /// Type marker for create_handle method
212 _marker: PhantomData<I>,
215 impl<I> ItemDetails<I> {
216 /// Construct a stable handle value from the item details
217 fn create_handle(&self) -> Handle<I> {
219 index: self.index as u32,
220 epoch: self.interned_epoch,
221 _marker: PhantomData,
226 /// The main interning data structure. This lives in the
227 /// scene builder thread, and handles hashing and interning
228 /// unique data structures. It also manages a free-list for
229 /// the items in the data store, which is synchronized via
230 /// an update list of additions / removals.
231 #[cfg_attr(feature = "capture", derive(Serialize))]
232 #[cfg_attr(feature = "replay", derive(Deserialize))]
233 #[derive(MallocSizeOf)]
234 pub struct Interner<I: Internable> {
235 /// Uniquely map an interning key to a handle
236 map: FastHashMap<I::Key, ItemDetails<I>>,
237 /// List of free slots in the data store for re-use.
238 free_list: Vec<usize>,
239 /// Pending list of updates that need to be applied.
240 update_list: UpdateList<I::Key>,
241 /// The current epoch for the interner.
242 current_epoch: Epoch,
243 /// The information associated with each interned
244 /// item that can be accessed by the interner.
245 local_data: Vec<I::InternData>,
248 impl<I: Internable> Default for Interner<I> {
249 fn default() -> Self {
251 map: FastHashMap::default(),
252 free_list: Vec::new(),
253 update_list: UpdateList::new(),
254 current_epoch: Epoch(1),
255 local_data: Vec::new(),
260 impl<I: Internable> Interner<I> {
261 /// Intern a data structure, and return a handle to
262 /// that data. The handle can then be stored in the
263 /// frame builder, and safely accessed via the data
264 /// store that lives in the frame builder thread.
265 /// The provided closure is invoked to build the
266 /// local data about an interned structure if the
267 /// key isn't already interned.
272 ) -> Handle<I> where F: FnOnce() -> I::InternData {
273 // Use get_mut rather than entry here to avoid
274 // cloning the (sometimes large) key in the common
275 // case, where the data already exists in the interner.
276 if let Some(details) = self.map.get_mut(data) {
277 // Update the last referenced frame for this element
278 details.last_used_epoch = self.current_epoch;
279 // Return a stable handle value for dependency checking
280 return details.create_handle();
283 // We need to intern a new data item. First, find out
284 // if there is a spare slot in the free-list that we
285 // can use. Otherwise, append to the end of the list.
286 let index = match self.free_list.pop() {
287 Some(index) => index,
288 None => self.local_data.len(),
291 // Generate a handle for access via the data store.
292 let handle = Handle {
294 epoch: self.current_epoch,
295 _marker: PhantomData,
298 let uid = handle.uid();
300 // Add a pending update to insert the new data.
301 self.update_list.insertions.push(Insertion {
307 #[cfg(debug_assertions)]
308 data.on_interned(uid);
310 // Store this handle so the next time it is
311 // interned, it gets re-used.
312 self.map.insert(data.clone(), ItemDetails {
313 interned_epoch: self.current_epoch,
314 last_used_epoch: self.current_epoch,
316 _marker: PhantomData,
319 // Create the local data for this item that is
321 self.local_data.entry(index).set(fun());
326 /// Retrieve the pending list of updates for an interner
327 /// that need to be applied to the data store. Also run
328 /// a GC step that removes old entries.
329 pub fn end_frame_and_get_pending_updates(&mut self) -> UpdateList<I::Key> {
330 let mut update_list = self.update_list.take_and_preallocate();
332 let free_list = &mut self.free_list;
333 let current_epoch = self.current_epoch.0;
335 // First, run a GC step. Walk through the handles, and
336 // if we find any that haven't been used for some time,
337 // remove them. If this ever shows up in profiles, we
338 // can make the GC step partial (scan only part of the
339 // map each frame). It also might make sense in the
340 // future to adjust how long items remain in the cache
341 // based on the current size of the list.
342 self.map.retain(|_, details| {
343 if details.last_used_epoch.0 + 10 < current_epoch {
344 // To expire an item:
345 // - Add index to the free-list for re-use.
346 // - Add an update to the data store to invalidate this slot.
347 // - Remove from the hash map.
348 free_list.push(details.index);
349 update_list.removals.push(Removal {
350 index: details.index,
351 uid: details.create_handle().uid(),
359 // Begin the next epoch
360 self.current_epoch = Epoch(self.current_epoch.0 + 1);
366 /// Retrieve the local data for an item from the interner via handle
367 impl<I: Internable> ops::Index<Handle<I>> for Interner<I> {
368 type Output = I::InternData;
369 fn index(&self, handle: Handle<I>) -> &I::InternData {
370 &self.local_data[handle.index as usize]
374 /// Meta-macro to enumerate the various interner identifiers and types.
376 /// IMPORTANT: Keep this synchronized with the list in mozilla-central located at
377 /// gfx/webrender_bindings/webrender_ffi.h
379 /// Note that this could be a lot less verbose if concat_idents! were stable. :-(
381 macro_rules! enumerate_interners {
382 ($macro_name: ident) => {
385 prim: PrimitiveKeyKind,
386 normal_border: NormalBorderPrim,
387 image_border: ImageBorder,
390 line_decoration: LineDecoration,
391 linear_grad: LinearGradient,
392 radial_grad: RadialGradient,
393 conic_grad: ConicGradient,
396 filter_data: FilterDataIntern,
398 polygon: PolygonIntern,
403 macro_rules! declare_interning_memory_report {
404 ( $( $name:ident: $ty:ident, )+ ) => {
407 #[derive(AddAssign, Clone, Debug, Default)]
408 pub struct InternerSubReport {
417 enumerate_interners!(declare_interning_memory_report);
419 /// Memory report for interning-related data structures.
420 /// cbindgen:derive-eq=false
421 /// cbindgen:derive-ostream=false
423 #[derive(Clone, Debug, Default)]
424 pub struct InterningMemoryReport {
426 pub interners: InternerSubReport,
428 pub data_stores: InternerSubReport,
431 impl ::std::ops::AddAssign for InterningMemoryReport {
432 fn add_assign(&mut self, other: InterningMemoryReport) {
433 self.interners += other.interners;
434 self.data_stores += other.data_stores;
438 // The trick to make trait bounds configurable by features.
440 #[cfg(not(feature = "capture"))]
441 pub trait Serialize {}
442 #[cfg(not(feature = "capture"))]
443 impl<T> Serialize for T {}
444 #[cfg(not(feature = "replay"))]
445 pub trait Deserialize<'a> {}
446 #[cfg(not(feature = "replay"))]
447 impl<'a, T> Deserialize<'a> for T {}
449 #[cfg(feature = "capture")]
450 use serde::Serialize as InternSerialize;
451 #[cfg(not(feature = "capture"))]
452 use self::dummy::Serialize as InternSerialize;
453 #[cfg(feature = "replay")]
454 use serde::Deserialize as InternDeserialize;
455 #[cfg(not(feature = "replay"))]
456 use self::dummy::Deserialize as InternDeserialize;
458 /// Implement `Internable` for a type that wants to participate in interning.
459 pub trait Internable: MallocSizeOf {
460 type Key: Eq + Hash + Clone + Debug + MallocSizeOf + InternDebug + InternSerialize + for<'a> InternDeserialize<'a>;
461 type StoreData: From<Self::Key> + MallocSizeOf + InternSerialize + for<'a> InternDeserialize<'a>;
462 type InternData: MallocSizeOf + InternSerialize + for<'a> InternDeserialize<'a>;
464 // Profile counter indices, see the list in profiler.rs
465 const PROFILE_COUNTER: usize;