1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
14 use sys_common::poison::{self, TryLockError, TryLockResult, LockResult};
15 use sys::mutex as sys;
17 /// A re-entrant mutual exclusion
19 /// This mutex will block *other* threads waiting for the lock to become
20 /// available. The thread which has already locked the mutex can lock it
21 /// multiple times without blocking, preventing a common source of deadlocks.
22 pub struct ReentrantMutex<T> {
23 inner: Box<sys::ReentrantMutex>,
28 unsafe impl<T: Send> Send for ReentrantMutex<T> {}
29 unsafe impl<T: Send> Sync for ReentrantMutex<T> {}
32 /// An RAII implementation of a "scoped lock" of a mutex. When this structure is
33 /// dropped (falls out of scope), the lock will be unlocked.
35 /// The data protected by the mutex can be accessed through this guard via its
36 /// Deref implementation.
40 /// Unlike `MutexGuard`, `ReentrantMutexGuard` does not implement `DerefMut`,
41 /// because implementation of the trait would violate Rust’s reference aliasing
42 /// rules. Use interior mutability (usually `RefCell`) in order to mutate the
45 pub struct ReentrantMutexGuard<'a, T: 'a> {
46 // funny underscores due to how Deref currently works (it disregards field
48 __lock: &'a ReentrantMutex<T>,
49 __poison: poison::Guard,
52 impl<'a, T> !marker::Send for ReentrantMutexGuard<'a, T> {}
55 impl<T> ReentrantMutex<T> {
56 /// Creates a new reentrant mutex in an unlocked state.
57 pub fn new(t: T) -> ReentrantMutex<T> {
59 let mut mutex = ReentrantMutex {
60 inner: box sys::ReentrantMutex::uninitialized(),
61 poison: poison::Flag::new(),
69 /// Acquires a mutex, blocking the current thread until it is able to do so.
71 /// This function will block the caller until it is available to acquire the mutex.
72 /// Upon returning, the thread is the only thread with the mutex held. When the thread
73 /// calling this method already holds the lock, the call shall succeed without
78 /// If another user of this mutex panicked while holding the mutex, then
79 /// this call will return failure if the mutex would otherwise be
81 pub fn lock(&self) -> LockResult<ReentrantMutexGuard<T>> {
82 unsafe { self.inner.lock() }
83 ReentrantMutexGuard::new(&self)
86 /// Attempts to acquire this lock.
88 /// If the lock could not be acquired at this time, then `Err` is returned.
89 /// Otherwise, an RAII guard is returned.
91 /// This function does not block.
95 /// If another user of this mutex panicked while holding the mutex, then
96 /// this call will return failure if the mutex would otherwise be
98 pub fn try_lock(&self) -> TryLockResult<ReentrantMutexGuard<T>> {
99 if unsafe { self.inner.try_lock() } {
100 Ok(ReentrantMutexGuard::new(&self)?)
102 Err(TryLockError::WouldBlock)
107 impl<T> Drop for ReentrantMutex<T> {
109 // This is actually safe b/c we know that there is no further usage of
110 // this mutex (it's up to the user to arrange for a mutex to get
111 // dropped, that's not our job)
112 unsafe { self.inner.destroy() }
116 impl<T: fmt::Debug + 'static> fmt::Debug for ReentrantMutex<T> {
117 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
118 match self.try_lock() {
119 Ok(guard) => write!(f, "ReentrantMutex {{ data: {:?} }}", &*guard),
120 Err(TryLockError::Poisoned(err)) => {
121 write!(f, "ReentrantMutex {{ data: Poisoned({:?}) }}", &**err.get_ref())
123 Err(TryLockError::WouldBlock) => write!(f, "ReentrantMutex {{ <locked> }}")
128 impl<'mutex, T> ReentrantMutexGuard<'mutex, T> {
129 fn new(lock: &'mutex ReentrantMutex<T>)
130 -> LockResult<ReentrantMutexGuard<'mutex, T>> {
131 poison::map_result(lock.poison.borrow(), |guard| {
132 ReentrantMutexGuard {
140 impl<'mutex, T> Deref for ReentrantMutexGuard<'mutex, T> {
143 fn deref(&self) -> &T {
148 impl<'a, T> Drop for ReentrantMutexGuard<'a, T> {
152 self.__lock.poison.done(&self.__poison);
153 self.__lock.inner.unlock();
161 use sys_common::remutex::{ReentrantMutex, ReentrantMutexGuard};
168 let m = ReentrantMutex::new(());
170 let a = m.lock().unwrap();
172 let b = m.lock().unwrap();
174 let c = m.lock().unwrap();
185 let m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
187 let lock = m.lock().unwrap();
188 let child = thread::spawn(move || {
189 let lock = m2.lock().unwrap();
190 assert_eq!(*lock.borrow(), 4950);
193 let lock = m.lock().unwrap();
194 *lock.borrow_mut() += i;
197 child.join().unwrap();
202 let m = Arc::new(ReentrantMutex::new(()));
204 let _lock = m.try_lock().unwrap();
205 let _lock2 = m.try_lock().unwrap();
206 thread::spawn(move || {
207 let lock = m2.try_lock();
208 assert!(lock.is_err());
210 let _lock3 = m.try_lock().unwrap();
213 pub struct Answer<'a>(pub ReentrantMutexGuard<'a, RefCell<u32>>);
214 impl<'a> Drop for Answer<'a> {
216 *self.0.borrow_mut() = 42;
222 let m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
224 let result = thread::spawn(move ||{
225 let lock = mc.lock().unwrap();
226 *lock.borrow_mut() = 1;
227 let lock2 = mc.lock().unwrap();
228 *lock.borrow_mut() = 2;
229 let _answer = Answer(lock2);
230 panic!("What the answer to my lifetimes dilemma is?");
232 assert!(result.is_err());
233 let r = m.lock().err().unwrap().into_inner();
234 assert_eq!(*r.borrow(), 42);