150 lines
4.8 KiB
Rust
150 lines
4.8 KiB
Rust
// Copyright 2016 Amanieu d'Antras
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//
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// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
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// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
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// http://opensource.org/licenses/MIT>, at your option. This file may not be
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// copied, modified, or distributed except according to those terms.
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use crate::raw_mutex::RawMutex;
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use core::num::NonZeroUsize;
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use lock_api::{self, GetThreadId};
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/// Implementation of the `GetThreadId` trait for `lock_api::ReentrantMutex`.
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pub struct RawThreadId;
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unsafe impl GetThreadId for RawThreadId {
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const INIT: RawThreadId = RawThreadId;
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fn nonzero_thread_id(&self) -> NonZeroUsize {
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// The address of a thread-local variable is guaranteed to be unique to the
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// current thread, and is also guaranteed to be non-zero. The variable has to have a
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// non-zero size to guarantee it has a unique address for each thread.
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thread_local!(static KEY: u8 = 0);
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KEY.with(|x| {
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NonZeroUsize::new(x as *const _ as usize)
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.expect("thread-local variable address is null")
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})
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}
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}
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/// A mutex which can be recursively locked by a single thread.
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///
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/// This type is identical to `Mutex` except for the following points:
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///
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/// - Locking multiple times from the same thread will work correctly instead of
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/// deadlocking.
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/// - `ReentrantMutexGuard` does not give mutable references to the locked data.
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/// Use a `RefCell` if you need this.
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///
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/// See [`Mutex`](type.Mutex.html) for more details about the underlying mutex
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/// primitive.
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pub type ReentrantMutex<T> = lock_api::ReentrantMutex<RawMutex, RawThreadId, T>;
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/// Creates a new reentrant mutex in an unlocked state ready for use.
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///
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/// This allows creating a reentrant mutex in a constant context on stable Rust.
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pub const fn const_reentrant_mutex<T>(val: T) -> ReentrantMutex<T> {
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ReentrantMutex::const_new(
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<RawMutex as lock_api::RawMutex>::INIT,
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<RawThreadId as lock_api::GetThreadId>::INIT,
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val,
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)
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}
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/// An RAII implementation of a "scoped lock" of a reentrant mutex. When this structure
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/// is dropped (falls out of scope), the lock will be unlocked.
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///
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/// The data protected by the mutex can be accessed through this guard via its
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/// `Deref` implementation.
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pub type ReentrantMutexGuard<'a, T> = lock_api::ReentrantMutexGuard<'a, RawMutex, RawThreadId, T>;
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/// An RAII mutex guard returned by `ReentrantMutexGuard::map`, which can point to a
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/// subfield of the protected data.
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///
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/// The main difference between `MappedReentrantMutexGuard` and `ReentrantMutexGuard` is that the
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/// former doesn't support temporarily unlocking and re-locking, since that
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/// could introduce soundness issues if the locked object is modified by another
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/// thread.
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pub type MappedReentrantMutexGuard<'a, T> =
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lock_api::MappedReentrantMutexGuard<'a, RawMutex, RawThreadId, T>;
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#[cfg(test)]
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mod tests {
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use crate::ReentrantMutex;
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use std::cell::RefCell;
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use std::sync::Arc;
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use std::thread;
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#[cfg(feature = "serde")]
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use bincode::{deserialize, serialize};
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#[test]
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fn smoke() {
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let m = ReentrantMutex::new(2);
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{
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let a = m.lock();
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{
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let b = m.lock();
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{
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let c = m.lock();
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assert_eq!(*c, 2);
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}
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assert_eq!(*b, 2);
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}
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assert_eq!(*a, 2);
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}
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}
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#[test]
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fn is_mutex() {
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let m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
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let m2 = m.clone();
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let lock = m.lock();
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let child = thread::spawn(move || {
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let lock = m2.lock();
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assert_eq!(*lock.borrow(), 4950);
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});
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for i in 0..100 {
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let lock = m.lock();
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*lock.borrow_mut() += i;
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}
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drop(lock);
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child.join().unwrap();
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}
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#[test]
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fn trylock_works() {
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let m = Arc::new(ReentrantMutex::new(()));
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let m2 = m.clone();
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let _lock = m.try_lock();
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let _lock2 = m.try_lock();
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thread::spawn(move || {
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let lock = m2.try_lock();
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assert!(lock.is_none());
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})
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.join()
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.unwrap();
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let _lock3 = m.try_lock();
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}
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#[test]
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fn test_reentrant_mutex_debug() {
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let mutex = ReentrantMutex::new(vec![0u8, 10]);
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assert_eq!(format!("{:?}", mutex), "ReentrantMutex { data: [0, 10] }");
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}
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#[cfg(feature = "serde")]
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#[test]
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fn test_serde() {
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let contents: Vec<u8> = vec![0, 1, 2];
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let mutex = ReentrantMutex::new(contents.clone());
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let serialized = serialize(&mutex).unwrap();
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let deserialized: ReentrantMutex<Vec<u8>> = deserialize(&serialized).unwrap();
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assert_eq!(*(mutex.lock()), *(deserialized.lock()));
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assert_eq!(contents, *(deserialized.lock()));
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}
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}
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