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ed9ed19cfb
<!-- Please describe your changes on the following line: --> --- <!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: --> - [X] `./mach build -d` does not report any errors - [X] `./mach test-tidy` does not report any errors - [X] These changes fix https://bugzilla.mozilla.org/show_bug.cgi?id=1369621 <!-- Either: --> - [ ] There are tests for these changes OR - [ ] These changes do not require tests because _____ <!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.--> <!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. --> Source-Repo: https://github.com/servo/servo Source-Revision: 612f2c1c2a9e56de2abe9ce32fcb6461a133686d --HG-- extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear extra : subtree_revision : 89a0524ef12c025009488f127ecc083a71ba646b
77 lines
2.6 KiB
Rust
77 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 http://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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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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/// Unsafe access to the slots. This can be used to access the TLS when
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/// the caller knows that the pool does not have access to the TLS.
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pub unsafe fn unsafe_get(&self) -> &[RefCell<Option<T>>] {
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&self.slots
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}
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}
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