mirror of
https://github.com/servo/servo.git
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e7cb736796
We only ever look at the slots after we are done with the thread pool, so we don't need to expose any unsafety to inspect the slots.
78 lines
2.6 KiB
Rust
78 lines
2.6 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 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: Box<[RefCell<Option<T>>]>,
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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(p: &'scope rayon::ThreadPool) -> Self {
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let count = p.current_num_threads();
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let mut v = Vec::with_capacity(count);
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for _ in 0..count {
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v.push(RefCell::new(None));
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}
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ScopedTLS {
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pool: p,
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slots: v.into_boxed_slice(),
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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, consuming the scope.
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pub fn into_slots(self) -> Box<[RefCell<Option<T>>]> {
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self.slots
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}
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}
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