95 lines
2.7 KiB
Rust
95 lines
2.7 KiB
Rust
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// Copyright 2016 Joe Wilm, The Alacritty Project Contributors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//! Synchronization types
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//!
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//! Most importantly, a priority mutex is included
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use std::ops::{Deref, DerefMut};
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use parking_lot::{Mutex, MutexGuard};
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/// A priority mutex
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///
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/// A triple locking strategy is used where low priority locks must go through an additional mutex
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/// to access the data. The gist is
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///
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/// Low priority: lock low, lock next, lock data, unlock next, {do work}, unlock data, unlock low
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/// High priority: lock next, lock data, unlock next, {do work}, unlock data
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///
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/// By keeping the low lock active while working on data, a high priority consumer has immediate
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/// access to the next mutex.
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pub struct PriorityMutex<T> {
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/// Data
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data: Mutex<T>,
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/// Next-to-access
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next: Mutex<()>,
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/// Low-priority access
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low: Mutex<()>,
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}
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/// Mutex guard for low priority locks
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pub struct LowPriorityMutexGuard<'a, T: 'a> {
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data: MutexGuard<'a, T>,
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_low: MutexGuard<'a, ()>,
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}
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impl<'a, T> Deref for LowPriorityMutexGuard<'a, T> {
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type Target = T;
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#[inline]
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fn deref(&self) -> &T {
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self.data.deref()
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}
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}
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impl<'a, T> DerefMut for LowPriorityMutexGuard<'a, T> {
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#[inline]
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fn deref_mut(&mut self) -> &mut T {
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self.data.deref_mut()
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}
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}
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impl<T> PriorityMutex<T> {
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/// Create a new priority mutex
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pub fn new(data: T) -> PriorityMutex<T> {
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PriorityMutex {
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data: Mutex::new(data),
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next: Mutex::new(()),
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low: Mutex::new(()),
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}
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}
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/// Lock the mutex with high priority
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pub fn lock_high(&self) -> MutexGuard<T> {
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// Must bind to a temporary or the lock will be freed before going
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// into data.lock()
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let _next = self.next.lock();
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self.data.lock()
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}
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/// Lock the mutex with low priority
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pub fn lock_low(&self) -> LowPriorityMutexGuard<T> {
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let low = self.low.lock();
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// Must bind to a temporary or the lock will be freed before going
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// into data.lock()
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let _next = self.next.lock();
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let data = self.data.lock();
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LowPriorityMutexGuard {
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data: data,
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_low: low,
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}
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}
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}
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