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 https://mozilla.org/MPL/2.0/. */ 4 5 //! Stack-scoped thread-local storage for rayon thread pools. 6 7 #![allow(unsafe_code)] 8 #![deny(missing_docs)] 9 10 use rayon; 11 use std::cell::{Ref, RefCell, RefMut}; 12 use std::ops::DerefMut; 13 14 /// A scoped TLS set, that is alive during the `'scope` lifetime. 15 /// 16 /// We use this on Servo to construct thread-local contexts, but clear them once 17 /// we're done with restyling. 18 /// 19 /// Note that the cleanup is done on the thread that owns the scoped TLS, thus 20 /// the Send bound. 21 pub struct ScopedTLS<'scope, T: Send> { 22 pool: &'scope rayon::ThreadPool, 23 slots: Box<[RefCell<Option<T>>]>, 24 } 25 26 /// The scoped TLS is `Sync` because no more than one worker thread can access a 27 /// given slot. 28 unsafe impl<'scope, T: Send> Sync for ScopedTLS<'scope, T> {} 29 30 impl<'scope, T: Send> ScopedTLS<'scope, T> { 31 /// Create a new scoped TLS that will last as long as this rayon threadpool 32 /// reference. new(p: &'scope rayon::ThreadPool) -> Self33 pub fn new(p: &'scope rayon::ThreadPool) -> Self { 34 let count = p.current_num_threads(); 35 let mut v = Vec::with_capacity(count); 36 for _ in 0..count { 37 v.push(RefCell::new(None)); 38 } 39 40 ScopedTLS { 41 pool: p, 42 slots: v.into_boxed_slice(), 43 } 44 } 45 46 /// Return an immutable reference to the `Option<T>` that this thread owns. borrow(&self) -> Ref<Option<T>>47 pub fn borrow(&self) -> Ref<Option<T>> { 48 let idx = self.pool.current_thread_index().unwrap(); 49 self.slots[idx].borrow() 50 } 51 52 /// Return a mutable reference to the `Option<T>` that this thread owns. borrow_mut(&self) -> RefMut<Option<T>>53 pub fn borrow_mut(&self) -> RefMut<Option<T>> { 54 let idx = self.pool.current_thread_index().unwrap(); 55 self.slots[idx].borrow_mut() 56 } 57 58 /// Ensure that the current data this thread owns is initialized, or 59 /// initialize it using `f`. We want ensure() to be fast and inline, and we 60 /// want to inline the memmove that initializes the Option<T>. But we don't 61 /// want to inline space for the entire large T struct in our stack frame. 62 /// That's why we hand `f` a mutable borrow to write to instead of just 63 /// having it return a T. 64 #[inline(always)] ensure<F: FnOnce(&mut Option<T>)>(&self, f: F) -> RefMut<T>65 pub fn ensure<F: FnOnce(&mut Option<T>)>(&self, f: F) -> RefMut<T> { 66 let mut opt = self.borrow_mut(); 67 if opt.is_none() { 68 f(opt.deref_mut()); 69 } 70 71 RefMut::map(opt, |x| x.as_mut().unwrap()) 72 } 73 74 /// Returns the slots, consuming the scope. into_slots(self) -> Box<[RefCell<Option<T>>]>75 pub fn into_slots(self) -> Box<[RefCell<Option<T>>]> { 76 self.slots 77 } 78 } 79