/* 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;
use peek_poke::PeekPoke;
#[cfg_attr(feature = "capture", derive(Serialize))]
#[cfg_attr(feature = "replay", derive(Deserialize))]
#[derive(Debug, Copy, Clone, Hash, MallocSizeOf, PartialEq, Eq)]
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, PeekPoke, Default)]
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, Hash, MallocSizeOf, PartialEq, Eq)]
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 const INVALID: Self = Handle { index: !0, epoch: Epoch(!0), _marker: PhantomData };
}
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_capture: BackdropCapture,
backdrop_render: BackdropRender,
polygon: PolygonIntern,
box_shadow: BoxShadow,
}
}
}
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> Intern
Deserialize<'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;
}
