1 // Copyright 2014 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.
16 use ops::{Deref, DerefMut};
17 use sys_common::mutex as sys;
18 use sys_common::poison::{self, TryLockError, TryLockResult, LockResult};
20 /// A mutual exclusion primitive useful for protecting shared data
22 /// This mutex will block threads waiting for the lock to become available. The
23 /// mutex can also be statically initialized or created via a `new`
24 /// constructor. Each mutex has a type parameter which represents the data that
25 /// it is protecting. The data can only be accessed through the RAII guards
26 /// returned from `lock` and `try_lock`, which guarantees that the data is only
27 /// ever accessed when the mutex is locked.
31 /// The mutexes in this module implement a strategy called "poisoning" where a
32 /// mutex is considered poisoned whenever a thread panics while holding the
33 /// lock. Once a mutex is poisoned, all other threads are unable to access the
34 /// data by default as it is likely tainted (some invariant is not being
37 /// For a mutex, this means that the `lock` and `try_lock` methods return a
38 /// `Result` which indicates whether a mutex has been poisoned or not. Most
39 /// usage of a mutex will simply `unwrap()` these results, propagating panics
40 /// among threads to ensure that a possibly invalid invariant is not witnessed.
42 /// A poisoned mutex, however, does not prevent all access to the underlying
43 /// data. The `PoisonError` type has an `into_inner` method which will return
44 /// the guard that would have otherwise been returned on a successful lock. This
45 /// allows access to the data, despite the lock being poisoned.
50 /// use std::sync::{Arc, Mutex};
52 /// use std::sync::mpsc::channel;
54 /// const N: usize = 10;
56 /// // Spawn a few threads to increment a shared variable (non-atomically), and
57 /// // let the main thread know once all increments are done.
59 /// // Here we're using an Arc to share memory among threads, and the data inside
60 /// // the Arc is protected with a mutex.
61 /// let data = Arc::new(Mutex::new(0));
63 /// let (tx, rx) = channel();
65 /// let (data, tx) = (data.clone(), tx.clone());
66 /// thread::spawn(move || {
67 /// // The shared static can only be accessed once the lock is held.
68 /// // Our non-atomic increment is safe because we're the only thread
69 /// // which can access the shared state when the lock is held.
71 /// // We unwrap() the return value to assert that we are not expecting
72 /// // threads to ever fail while holding the lock.
73 /// let mut data = data.lock().unwrap();
76 /// tx.send(()).unwrap();
78 /// // the lock is unlocked here when `data` goes out of scope.
82 /// rx.recv().unwrap();
85 /// To recover from a poisoned mutex:
88 /// use std::sync::{Arc, Mutex};
91 /// let lock = Arc::new(Mutex::new(0_u32));
92 /// let lock2 = lock.clone();
94 /// let _ = thread::spawn(move || -> () {
95 /// // This thread will acquire the mutex first, unwrapping the result of
96 /// // `lock` because the lock has not been poisoned.
97 /// let _lock = lock2.lock().unwrap();
99 /// // This panic while holding the lock (`_guard` is in scope) will poison
104 /// // The lock is poisoned by this point, but the returned result can be
105 /// // pattern matched on to return the underlying guard on both branches.
106 /// let mut guard = match lock.lock() {
107 /// Ok(guard) => guard,
108 /// Err(poisoned) => poisoned.into_inner(),
113 #[stable(feature = "rust1", since = "1.0.0")]
114 pub struct Mutex<T: ?Sized> {
115 // Note that this static mutex is in a *box*, not inlined into the struct
116 // itself. Once a native mutex has been used once, its address can never
117 // change (it can't be moved). This mutex type can be safely moved at any
118 // time, so to ensure that the native mutex is used correctly we box the
119 // inner lock to give it a constant address.
120 inner: Box<StaticMutex>,
124 // these are the only places where `T: Send` matters; all other
125 // functionality works fine on a single thread.
126 unsafe impl<T: ?Sized + Send> Send for Mutex<T> { }
128 unsafe impl<T: ?Sized + Send> Sync for Mutex<T> { }
130 /// The static mutex type is provided to allow for static allocation of mutexes.
132 /// Note that this is a separate type because using a Mutex correctly means that
133 /// it needs to have a destructor run. In Rust, statics are not allowed to have
134 /// destructors. As a result, a `StaticMutex` has one extra method when compared
135 /// to a `Mutex`, a `destroy` method. This method is unsafe to call, and
136 /// documentation can be found directly on the method.
141 /// #![feature(static_mutex)]
143 /// use std::sync::{StaticMutex, MUTEX_INIT};
145 /// static LOCK: StaticMutex = MUTEX_INIT;
148 /// let _g = LOCK.lock().unwrap();
149 /// // do some productive work
151 /// // lock is unlocked here.
153 #[unstable(feature = "static_mutex",
154 reason = "may be merged with Mutex in the future",
156 pub struct StaticMutex {
158 poison: poison::Flag,
161 /// An RAII implementation of a "scoped lock" of a mutex. When this structure is
162 /// dropped (falls out of scope), the lock will be unlocked.
164 /// The data protected by the mutex can be access through this guard via its
165 /// `Deref` and `DerefMut` implementations
167 #[stable(feature = "rust1", since = "1.0.0")]
168 pub struct MutexGuard<'a, T: ?Sized + 'a> {
169 // funny underscores due to how Deref/DerefMut currently work (they
170 // disregard field privacy).
171 __lock: &'a StaticMutex,
172 __data: &'a UnsafeCell<T>,
173 __poison: poison::Guard,
176 impl<'a, T: ?Sized> !marker::Send for MutexGuard<'a, T> {}
178 /// Static initialization of a mutex. This constant can be used to initialize
179 /// other mutex constants.
180 #[unstable(feature = "static_mutex",
181 reason = "may be merged with Mutex in the future",
183 pub const MUTEX_INIT: StaticMutex = StaticMutex::new();
186 /// Creates a new mutex in an unlocked state ready for use.
187 #[stable(feature = "rust1", since = "1.0.0")]
188 pub fn new(t: T) -> Mutex<T> {
190 inner: box StaticMutex::new(),
191 data: UnsafeCell::new(t),
196 impl<T: ?Sized> Mutex<T> {
197 /// Acquires a mutex, blocking the current thread until it is able to do so.
199 /// This function will block the local thread until it is available to acquire
200 /// the mutex. Upon returning, the thread is the only thread with the mutex
201 /// held. An RAII guard is returned to allow scoped unlock of the lock. When
202 /// the guard goes out of scope, the mutex will be unlocked.
206 /// If another user of this mutex panicked while holding the mutex, then
207 /// this call will return an error once the mutex is acquired.
208 #[stable(feature = "rust1", since = "1.0.0")]
209 pub fn lock(&self) -> LockResult<MutexGuard<T>> {
210 unsafe { self.inner.lock.lock() }
211 MutexGuard::new(&*self.inner, &self.data)
214 /// Attempts to acquire this lock.
216 /// If the lock could not be acquired at this time, then `Err` is returned.
217 /// Otherwise, an RAII guard is returned. The lock will be unlocked when the
218 /// guard is dropped.
220 /// This function does not block.
224 /// If another user of this mutex panicked while holding the mutex, then
225 /// this call will return failure if the mutex would otherwise be
227 #[stable(feature = "rust1", since = "1.0.0")]
228 pub fn try_lock(&self) -> TryLockResult<MutexGuard<T>> {
229 if unsafe { self.inner.lock.try_lock() } {
230 Ok(try!(MutexGuard::new(&*self.inner, &self.data)))
232 Err(TryLockError::WouldBlock)
236 /// Determines whether the lock is poisoned.
238 /// If another thread is active, the lock can still become poisoned at any
239 /// time. You should not trust a `false` value for program correctness
240 /// without additional synchronization.
242 #[stable(feature = "sync_poison", since = "1.2.0")]
243 pub fn is_poisoned(&self) -> bool {
244 self.inner.poison.get()
248 #[stable(feature = "rust1", since = "1.0.0")]
249 impl<T: ?Sized> Drop for Mutex<T> {
251 // This is actually safe b/c we know that there is no further usage of
252 // this mutex (it's up to the user to arrange for a mutex to get
253 // dropped, that's not our job)
254 unsafe { self.inner.lock.destroy() }
258 #[stable(feature = "rust1", since = "1.0.0")]
259 impl<T: ?Sized + fmt::Debug + 'static> fmt::Debug for Mutex<T> {
260 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
261 match self.try_lock() {
262 Ok(guard) => write!(f, "Mutex {{ data: {:?} }}", &*guard),
263 Err(TryLockError::Poisoned(err)) => {
264 write!(f, "Mutex {{ data: Poisoned({:?}) }}", &**err.get_ref())
266 Err(TryLockError::WouldBlock) => write!(f, "Mutex {{ <locked> }}")
271 struct Dummy(UnsafeCell<()>);
272 unsafe impl Sync for Dummy {}
273 static DUMMY: Dummy = Dummy(UnsafeCell::new(()));
275 #[unstable(feature = "static_mutex",
276 reason = "may be merged with Mutex in the future",
279 /// Creates a new mutex in an unlocked state ready for use.
280 pub const fn new() -> StaticMutex {
282 lock: sys::Mutex::new(),
283 poison: poison::Flag::new(),
287 /// Acquires this lock, see `Mutex::lock`
289 pub fn lock(&'static self) -> LockResult<MutexGuard<()>> {
290 unsafe { self.lock.lock() }
291 MutexGuard::new(self, &DUMMY.0)
294 /// Attempts to grab this lock, see `Mutex::try_lock`
296 pub fn try_lock(&'static self) -> TryLockResult<MutexGuard<()>> {
297 if unsafe { self.lock.try_lock() } {
298 Ok(try!(MutexGuard::new(self, &DUMMY.0)))
300 Err(TryLockError::WouldBlock)
304 /// Deallocates resources associated with this static mutex.
306 /// This method is unsafe because it provides no guarantees that there are
307 /// no active users of this mutex, and safety is not guaranteed if there are
308 /// active users of this mutex.
310 /// This method is required to ensure that there are no memory leaks on
311 /// *all* platforms. It may be the case that some platforms do not leak
312 /// memory if this method is not called, but this is not guaranteed to be
313 /// true on all platforms.
314 pub unsafe fn destroy(&'static self) {
319 impl<'mutex, T: ?Sized> MutexGuard<'mutex, T> {
321 fn new(lock: &'mutex StaticMutex, data: &'mutex UnsafeCell<T>)
322 -> LockResult<MutexGuard<'mutex, T>> {
323 poison::map_result(lock.poison.borrow(), |guard| {
333 #[stable(feature = "rust1", since = "1.0.0")]
334 impl<'mutex, T: ?Sized> Deref for MutexGuard<'mutex, T> {
337 fn deref<'a>(&'a self) -> &'a T {
338 unsafe { &*self.__data.get() }
341 #[stable(feature = "rust1", since = "1.0.0")]
342 impl<'mutex, T: ?Sized> DerefMut for MutexGuard<'mutex, T> {
343 fn deref_mut<'a>(&'a mut self) -> &'a mut T {
344 unsafe { &mut *self.__data.get() }
348 #[stable(feature = "rust1", since = "1.0.0")]
349 impl<'a, T: ?Sized> Drop for MutexGuard<'a, T> {
353 self.__lock.poison.done(&self.__poison);
354 self.__lock.lock.unlock();
359 pub fn guard_lock<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a sys::Mutex {
363 pub fn guard_poison<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a poison::Flag {
371 use sync::mpsc::channel;
372 use sync::{Arc, Mutex, StaticMutex, Condvar};
375 struct Packet<T>(Arc<(Mutex<T>, Condvar)>);
377 unsafe impl<T: Send> Send for Packet<T> {}
378 unsafe impl<T> Sync for Packet<T> {}
382 let m = Mutex::new(());
383 drop(m.lock().unwrap());
384 drop(m.lock().unwrap());
389 static M: StaticMutex = StaticMutex::new();
391 drop(M.lock().unwrap());
392 drop(M.lock().unwrap());
399 static M: StaticMutex = StaticMutex::new();
400 static mut CNT: u32 = 0;
407 let _g = M.lock().unwrap();
413 let (tx, rx) = channel();
415 let tx2 = tx.clone();
416 thread::spawn(move|| { inc(); tx2.send(()).unwrap(); });
417 let tx2 = tx.clone();
418 thread::spawn(move|| { inc(); tx2.send(()).unwrap(); });
425 assert_eq!(unsafe {CNT}, J * K * 2);
433 let m = Mutex::new(());
434 *m.try_lock().unwrap() = ();
438 fn test_mutex_arc_condvar() {
439 let packet = Packet(Arc::new((Mutex::new(false), Condvar::new())));
440 let packet2 = Packet(packet.0.clone());
441 let (tx, rx) = channel();
442 let _t = thread::spawn(move|| {
443 // wait until parent gets in
445 let &(ref lock, ref cvar) = &*packet2.0;
446 let mut lock = lock.lock().unwrap();
451 let &(ref lock, ref cvar) = &*packet.0;
452 let mut lock = lock.lock().unwrap();
453 tx.send(()).unwrap();
456 lock = cvar.wait(lock).unwrap();
461 fn test_arc_condvar_poison() {
462 let packet = Packet(Arc::new((Mutex::new(1), Condvar::new())));
463 let packet2 = Packet(packet.0.clone());
464 let (tx, rx) = channel();
466 let _t = thread::spawn(move || -> () {
468 let &(ref lock, ref cvar) = &*packet2.0;
469 let _g = lock.lock().unwrap();
471 // Parent should fail when it wakes up.
475 let &(ref lock, ref cvar) = &*packet.0;
476 let mut lock = lock.lock().unwrap();
477 tx.send(()).unwrap();
479 match cvar.wait(lock) {
482 assert_eq!(*lock, 1);
490 fn test_mutex_arc_poison() {
491 let arc = Arc::new(Mutex::new(1));
492 assert!(!arc.is_poisoned());
493 let arc2 = arc.clone();
494 let _ = thread::spawn(move|| {
495 let lock = arc2.lock().unwrap();
496 assert_eq!(*lock, 2);
498 assert!(arc.lock().is_err());
499 assert!(arc.is_poisoned());
503 fn test_mutex_arc_nested() {
504 // Tests nested mutexes and access
505 // to underlying data.
506 let arc = Arc::new(Mutex::new(1));
507 let arc2 = Arc::new(Mutex::new(arc));
508 let (tx, rx) = channel();
509 let _t = thread::spawn(move|| {
510 let lock = arc2.lock().unwrap();
511 let lock2 = lock.lock().unwrap();
512 assert_eq!(*lock2, 1);
513 tx.send(()).unwrap();
519 fn test_mutex_arc_access_in_unwind() {
520 let arc = Arc::new(Mutex::new(1));
521 let arc2 = arc.clone();
522 let _ = thread::spawn(move|| -> () {
526 impl Drop for Unwinder {
528 *self.i.lock().unwrap() += 1;
531 let _u = Unwinder { i: arc2 };
534 let lock = arc.lock().unwrap();
535 assert_eq!(*lock, 2);
538 // FIXME(#25351) needs deeply nested coercions of DST structs.
540 // fn test_mutex_unsized() {
541 // let mutex: &Mutex<[i32]> = &Mutex::new([1, 2, 3]);
543 // let b = &mut *mutex.lock().unwrap();
547 // let comp: &[i32] = &[4, 2, 5];
548 // assert_eq!(&*mutex.lock().unwrap(), comp);