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.
11 #![unstable(feature = "reentrant_mutex", reason = "new API",
19 use sys_common::poison::{self, TryLockError, TryLockResult, LockResult};
20 use sys::mutex as sys;
22 /// A re-entrant mutual exclusion
24 /// This mutex will block *other* threads waiting for the lock to become
25 /// available. The thread which has already locked the mutex can lock it
26 /// multiple times without blocking, preventing a common source of deadlocks.
27 pub struct ReentrantMutex<T> {
28 inner: Box<sys::ReentrantMutex>,
33 unsafe impl<T: Send> Send for ReentrantMutex<T> {}
34 unsafe impl<T: Send> Sync for ReentrantMutex<T> {}
37 /// An RAII implementation of a "scoped lock" of a mutex. When this structure is
38 /// dropped (falls out of scope), the lock will be unlocked.
40 /// The data protected by the mutex can be accessed through this guard via its
41 /// Deref implementation.
45 /// Unlike `MutexGuard`, `ReentrantMutexGuard` does not implement `DerefMut`,
46 /// because implementation of the trait would violate Rust’s reference aliasing
47 /// rules. Use interior mutability (usually `RefCell`) in order to mutate the
50 pub struct ReentrantMutexGuard<'a, T: 'a> {
51 // funny underscores due to how Deref currently works (it disregards field
53 __lock: &'a ReentrantMutex<T>,
54 __poison: poison::Guard,
57 impl<'a, T> !marker::Send for ReentrantMutexGuard<'a, T> {}
60 impl<T> ReentrantMutex<T> {
61 /// Creates a new reentrant mutex in an unlocked state.
62 pub fn new(t: T) -> ReentrantMutex<T> {
64 let mut mutex = ReentrantMutex {
65 inner: box sys::ReentrantMutex::uninitialized(),
66 poison: poison::Flag::new(),
74 /// Acquires a mutex, blocking the current thread until it is able to do so.
76 /// This function will block the caller until it is available to acquire the mutex.
77 /// Upon returning, the thread is the only thread with the mutex held. When the thread
78 /// calling this method already holds the lock, the call shall succeed without
83 /// If another user of this mutex panicked while holding the mutex, then
84 /// this call will return failure if the mutex would otherwise be
86 pub fn lock(&self) -> LockResult<ReentrantMutexGuard<T>> {
87 unsafe { self.inner.lock() }
88 ReentrantMutexGuard::new(&self)
91 /// Attempts to acquire this lock.
93 /// If the lock could not be acquired at this time, then `Err` is returned.
94 /// Otherwise, an RAII guard is returned.
96 /// This function does not block.
100 /// If another user of this mutex panicked while holding the mutex, then
101 /// this call will return failure if the mutex would otherwise be
103 pub fn try_lock(&self) -> TryLockResult<ReentrantMutexGuard<T>> {
104 if unsafe { self.inner.try_lock() } {
105 Ok(try!(ReentrantMutexGuard::new(&self)))
107 Err(TryLockError::WouldBlock)
112 impl<T> Drop for ReentrantMutex<T> {
114 // This is actually safe b/c we know that there is no further usage of
115 // this mutex (it's up to the user to arrange for a mutex to get
116 // dropped, that's not our job)
117 unsafe { self.inner.destroy() }
121 impl<T: fmt::Debug + 'static> fmt::Debug for ReentrantMutex<T> {
122 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
123 match self.try_lock() {
124 Ok(guard) => write!(f, "ReentrantMutex {{ data: {:?} }}", &*guard),
125 Err(TryLockError::Poisoned(err)) => {
126 write!(f, "ReentrantMutex {{ data: Poisoned({:?}) }}", &**err.get_ref())
128 Err(TryLockError::WouldBlock) => write!(f, "ReentrantMutex {{ <locked> }}")
133 impl<'mutex, T> ReentrantMutexGuard<'mutex, T> {
134 fn new(lock: &'mutex ReentrantMutex<T>)
135 -> LockResult<ReentrantMutexGuard<'mutex, T>> {
136 poison::map_result(lock.poison.borrow(), |guard| {
137 ReentrantMutexGuard {
145 impl<'mutex, T> Deref for ReentrantMutexGuard<'mutex, T> {
148 fn deref(&self) -> &T {
153 impl<'a, T> Drop for ReentrantMutexGuard<'a, T> {
157 self.__lock.poison.done(&self.__poison);
158 self.__lock.inner.unlock();
167 use sys_common::remutex::{ReentrantMutex, ReentrantMutexGuard};
175 let m = ReentrantMutex::new(());
177 let a = m.lock().unwrap();
179 let b = m.lock().unwrap();
181 let c = m.lock().unwrap();
192 let m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
194 let lock = m.lock().unwrap();
195 let child = thread::spawn(move || {
196 let lock = m2.lock().unwrap();
197 assert_eq!(*lock.borrow(), 4950);
200 let lock = m.lock().unwrap();
201 *lock.borrow_mut() += i;
204 child.join().unwrap();
209 let m = Arc::new(ReentrantMutex::new(()));
211 let lock = m.try_lock().unwrap();
212 let lock2 = m.try_lock().unwrap();
213 thread::spawn(move || {
214 let lock = m2.try_lock();
215 assert!(lock.is_err());
217 let lock3 = m.try_lock().unwrap();
220 pub struct Answer<'a>(pub ReentrantMutexGuard<'a, RefCell<u32>>);
221 impl<'a> Drop for Answer<'a> {
223 *self.0.borrow_mut() = 42;
229 let m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
231 let result = thread::spawn(move ||{
232 let lock = mc.lock().unwrap();
233 *lock.borrow_mut() = 1;
234 let lock2 = mc.lock().unwrap();
235 *lock.borrow_mut() = 2;
236 let answer = Answer(lock2);
237 panic!("What the answer to my lifetimes dilemma is?");
240 assert!(result.is_err());
241 let r = m.lock().err().unwrap().into_inner();
242 assert_eq!(*r.borrow(), 42);