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23d60c2195
Use in_place_scope_fifo to spawn work into the thread pool while doing work in the main thread. Differential Revision: https://phabricator.services.mozilla.com/D179492
75 lines
2.7 KiB
Rust
75 lines
2.7 KiB
Rust
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
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//! Stack-scoped thread-local storage for rayon thread pools.
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#![allow(unsafe_code)]
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#![deny(missing_docs)]
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use crate::global_style_data::STYLO_MAX_THREADS;
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use rayon;
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use std::cell::{Ref, RefCell, RefMut};
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use std::ops::DerefMut;
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/// A scoped TLS set, that is alive during the `'scope` lifetime.
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///
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/// We use this on Servo to construct thread-local contexts, but clear them once
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/// we're done with restyling.
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///
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/// Note that the cleanup is done on the thread that owns the scoped TLS, thus
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/// the Send bound.
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pub struct ScopedTLS<'scope, T: Send> {
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pool: &'scope rayon::ThreadPool,
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slots: [RefCell<Option<T>>; STYLO_MAX_THREADS],
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}
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/// The scoped TLS is `Sync` because no more than one worker thread can access a
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/// given slot.
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unsafe impl<'scope, T: Send> Sync for ScopedTLS<'scope, T> {}
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impl<'scope, T: Send> ScopedTLS<'scope, T> {
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/// Create a new scoped TLS that will last as long as this rayon threadpool
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/// reference.
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pub fn new(pool: &'scope rayon::ThreadPool) -> Self {
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debug_assert!(pool.current_num_threads() <= STYLO_MAX_THREADS);
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ScopedTLS {
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pool,
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slots: Default::default(),
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}
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}
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/// Return an immutable reference to the `Option<T>` that this thread owns.
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pub fn borrow(&self) -> Ref<Option<T>> {
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let idx = self.pool.current_thread_index().unwrap();
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self.slots[idx].borrow()
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}
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/// Return a mutable reference to the `Option<T>` that this thread owns.
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pub fn borrow_mut(&self) -> RefMut<Option<T>> {
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let idx = self.pool.current_thread_index().unwrap();
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self.slots[idx].borrow_mut()
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}
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/// Ensure that the current data this thread owns is initialized, or
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/// initialize it using `f`. We want ensure() to be fast and inline, and we
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/// want to inline the memmove that initializes the Option<T>. But we don't
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/// want to inline space for the entire large T struct in our stack frame.
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/// That's why we hand `f` a mutable borrow to write to instead of just
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/// having it return a T.
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#[inline(always)]
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pub fn ensure<F: FnOnce(&mut Option<T>)>(&self, f: F) -> RefMut<T> {
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let mut opt = self.borrow_mut();
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if opt.is_none() {
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f(opt.deref_mut());
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}
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RefMut::map(opt, |x| x.as_mut().unwrap())
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}
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/// Returns the slots. Safe because if we have a mut reference the tls can't be referenced by
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/// any other thread.
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pub fn slots(&mut self) -> &mut [RefCell<Option<T>>] {
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&mut self.slots
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}
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}
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