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.
14 use ops::{Deref, DerefMut};
16 use sys_common::mutex as sys;
17 use sys_common::poison::{self, TryLockError, TryLockResult, LockResult};
19 /// A mutual exclusion primitive useful for protecting shared data
21 /// This mutex will block threads waiting for the lock to become available. The
22 /// mutex can also be statically initialized or created via a `new`
23 /// constructor. Each mutex has a type parameter which represents the data that
24 /// it is protecting. The data can only be accessed through the RAII guards
25 /// returned from `lock` and `try_lock`, which guarantees that the data is only
26 /// ever accessed when the mutex is locked.
30 /// The mutexes in this module implement a strategy called "poisoning" where a
31 /// mutex is considered poisoned whenever a thread panics while holding the
32 /// mutex. Once a mutex is poisoned, all other threads are unable to access the
33 /// data by default as it is likely tainted (some invariant is not being
36 /// For a mutex, this means that the `lock` and `try_lock` methods return a
37 /// `Result` which indicates whether a mutex has been poisoned or not. Most
38 /// usage of a mutex will simply `unwrap()` these results, propagating panics
39 /// among threads to ensure that a possibly invalid invariant is not witnessed.
41 /// A poisoned mutex, however, does not prevent all access to the underlying
42 /// data. The `PoisonError` type has an `into_inner` method which will return
43 /// the guard that would have otherwise been returned on a successful lock. This
44 /// allows access to the data, despite the lock being poisoned.
49 /// use std::sync::{Arc, Mutex};
51 /// use std::sync::mpsc::channel;
53 /// const N: usize = 10;
55 /// // Spawn a few threads to increment a shared variable (non-atomically), and
56 /// // let the main thread know once all increments are done.
58 /// // Here we're using an Arc to share memory among threads, and the data inside
59 /// // the Arc is protected with a mutex.
60 /// let data = Arc::new(Mutex::new(0));
62 /// let (tx, rx) = channel();
64 /// let (data, tx) = (data.clone(), tx.clone());
65 /// thread::spawn(move || {
66 /// // The shared state can only be accessed once the lock is held.
67 /// // Our non-atomic increment is safe because we're the only thread
68 /// // which can access the shared state when the lock is held.
70 /// // We unwrap() the return value to assert that we are not expecting
71 /// // threads to ever fail while holding the lock.
72 /// let mut data = data.lock().unwrap();
75 /// tx.send(()).unwrap();
77 /// // the lock is unlocked here when `data` goes out of scope.
81 /// rx.recv().unwrap();
84 /// To recover from a poisoned mutex:
87 /// use std::sync::{Arc, Mutex};
90 /// let lock = Arc::new(Mutex::new(0_u32));
91 /// let lock2 = lock.clone();
93 /// let _ = thread::spawn(move || -> () {
94 /// // This thread will acquire the mutex first, unwrapping the result of
95 /// // `lock` because the lock has not been poisoned.
96 /// let _guard = lock2.lock().unwrap();
98 /// // This panic while holding the lock (`_guard` is in scope) will poison
103 /// // The lock is poisoned by this point, but the returned result can be
104 /// // pattern matched on to return the underlying guard on both branches.
105 /// let mut guard = match lock.lock() {
106 /// Ok(guard) => guard,
107 /// Err(poisoned) => poisoned.into_inner(),
112 #[stable(feature = "rust1", since = "1.0.0")]
113 pub struct Mutex<T: ?Sized> {
114 // Note that this mutex is in a *box*, not inlined into the struct itself.
115 // Once a native mutex has been used once, its address can never change (it
116 // can't be moved). This mutex type can be safely moved at any time, so to
117 // ensure that the native mutex is used correctly we box the inner mutex to
118 // give it a constant address.
119 inner: Box<sys::Mutex>,
120 poison: poison::Flag,
124 // these are the only places where `T: Send` matters; all other
125 // functionality works fine on a single thread.
126 #[stable(feature = "rust1", since = "1.0.0")]
127 unsafe impl<T: ?Sized + Send> Send for Mutex<T> { }
128 #[stable(feature = "rust1", since = "1.0.0")]
129 unsafe impl<T: ?Sized + Send> Sync for Mutex<T> { }
131 /// An RAII implementation of a "scoped lock" of a mutex. When this structure is
132 /// dropped (falls out of scope), the lock will be unlocked.
134 /// The data protected by the mutex can be accessed through this guard via its
135 /// [`Deref`] and [`DerefMut`] implementations.
137 /// This structure is created by the [`lock`] and [`try_lock`] methods on
140 /// [`Deref`]: ../../std/ops/trait.Deref.html
141 /// [`DerefMut`]: ../../std/ops/trait.DerefMut.html
142 /// [`lock`]: struct.Mutex.html#method.lock
143 /// [`try_lock`]: struct.Mutex.html#method.try_lock
144 /// [`Mutex`]: struct.Mutex.html
146 #[stable(feature = "rust1", since = "1.0.0")]
147 pub struct MutexGuard<'a, T: ?Sized + 'a> {
148 // funny underscores due to how Deref/DerefMut currently work (they
149 // disregard field privacy).
150 __lock: &'a Mutex<T>,
151 __poison: poison::Guard,
154 #[stable(feature = "rust1", since = "1.0.0")]
155 impl<'a, T: ?Sized> !Send for MutexGuard<'a, T> { }
156 #[stable(feature = "mutexguard", since = "1.19.0")]
157 unsafe impl<'a, T: ?Sized + Sync> Sync for MutexGuard<'a, T> { }
160 /// Creates a new mutex in an unlocked state ready for use.
165 /// use std::sync::Mutex;
167 /// let mutex = Mutex::new(0);
169 #[stable(feature = "rust1", since = "1.0.0")]
170 pub fn new(t: T) -> Mutex<T> {
172 inner: box sys::Mutex::new(),
173 poison: poison::Flag::new(),
174 data: UnsafeCell::new(t),
183 impl<T: ?Sized> Mutex<T> {
184 /// Acquires a mutex, blocking the current thread until it is able to do so.
186 /// This function will block the local thread until it is available to acquire
187 /// the mutex. Upon returning, the thread is the only thread with the lock
188 /// held. An RAII guard is returned to allow scoped unlock of the lock. When
189 /// the guard goes out of scope, the mutex will be unlocked.
191 /// The exact behavior on locking a mutex in the thread which already holds
192 /// the lock is left unspecified. However, this function will not return on
193 /// the second call (it might panic or deadlock, for example).
197 /// If another user of this mutex panicked while holding the mutex, then
198 /// this call will return an error once the mutex is acquired.
202 /// This function might panic when called if the lock is already held by
203 /// the current thread.
208 /// use std::sync::{Arc, Mutex};
211 /// let mutex = Arc::new(Mutex::new(0));
212 /// let c_mutex = mutex.clone();
214 /// thread::spawn(move || {
215 /// *c_mutex.lock().unwrap() = 10;
216 /// }).join().expect("thread::spawn failed");
217 /// assert_eq!(*mutex.lock().unwrap(), 10);
219 #[stable(feature = "rust1", since = "1.0.0")]
220 pub fn lock(&self) -> LockResult<MutexGuard<T>> {
223 MutexGuard::new(self)
227 /// Attempts to acquire this lock.
229 /// If the lock could not be acquired at this time, then `Err` is returned.
230 /// Otherwise, an RAII guard is returned. The lock will be unlocked when the
231 /// guard is dropped.
233 /// This function does not block.
237 /// If another user of this mutex panicked while holding the mutex, then
238 /// this call will return failure if the mutex would otherwise be
244 /// use std::sync::{Arc, Mutex};
247 /// let mutex = Arc::new(Mutex::new(0));
248 /// let c_mutex = mutex.clone();
250 /// thread::spawn(move || {
251 /// let mut lock = c_mutex.try_lock();
252 /// if let Ok(ref mut mutex) = lock {
255 /// println!("try_lock failed");
257 /// }).join().expect("thread::spawn failed");
258 /// assert_eq!(*mutex.lock().unwrap(), 10);
260 #[stable(feature = "rust1", since = "1.0.0")]
261 pub fn try_lock(&self) -> TryLockResult<MutexGuard<T>> {
263 if self.inner.try_lock() {
264 Ok(MutexGuard::new(self)?)
266 Err(TryLockError::WouldBlock)
271 /// Determines whether the mutex is poisoned.
273 /// If another thread is active, the mutex can still become poisoned at any
274 /// time. You should not trust a `false` value for program correctness
275 /// without additional synchronization.
280 /// use std::sync::{Arc, Mutex};
283 /// let mutex = Arc::new(Mutex::new(0));
284 /// let c_mutex = mutex.clone();
286 /// let _ = thread::spawn(move || {
287 /// let _lock = c_mutex.lock().unwrap();
288 /// panic!(); // the mutex gets poisoned
290 /// assert_eq!(mutex.is_poisoned(), true);
293 #[stable(feature = "sync_poison", since = "1.2.0")]
294 pub fn is_poisoned(&self) -> bool {
298 /// Consumes this mutex, returning the underlying data.
302 /// If another user of this mutex panicked while holding the mutex, then
303 /// this call will return an error instead.
308 /// use std::sync::Mutex;
310 /// let mutex = Mutex::new(0);
311 /// assert_eq!(mutex.into_inner().unwrap(), 0);
313 #[stable(feature = "mutex_into_inner", since = "1.6.0")]
314 pub fn into_inner(self) -> LockResult<T> where T: Sized {
315 // We know statically that there are no outstanding references to
316 // `self` so there's no need to lock the inner mutex.
318 // To get the inner value, we'd like to call `data.into_inner()`,
319 // but because `Mutex` impl-s `Drop`, we can't move out of it, so
320 // we'll have to destructure it manually instead.
322 // Like `let Mutex { inner, poison, data } = self`.
323 let (inner, poison, data) = {
324 let Mutex { ref inner, ref poison, ref data } = self;
325 (ptr::read(inner), ptr::read(poison), ptr::read(data))
328 inner.destroy(); // Keep in sync with the `Drop` impl.
331 poison::map_result(poison.borrow(), |_| data.into_inner())
335 /// Returns a mutable reference to the underlying data.
337 /// Since this call borrows the `Mutex` mutably, no actual locking needs to
338 /// take place---the mutable borrow statically guarantees no locks exist.
342 /// If another user of this mutex panicked while holding the mutex, then
343 /// this call will return an error instead.
348 /// use std::sync::Mutex;
350 /// let mut mutex = Mutex::new(0);
351 /// *mutex.get_mut().unwrap() = 10;
352 /// assert_eq!(*mutex.lock().unwrap(), 10);
354 #[stable(feature = "mutex_get_mut", since = "1.6.0")]
355 pub fn get_mut(&mut self) -> LockResult<&mut T> {
356 // We know statically that there are no other references to `self`, so
357 // there's no need to lock the inner mutex.
358 let data = unsafe { &mut *self.data.get() };
359 poison::map_result(self.poison.borrow(), |_| data )
363 #[stable(feature = "rust1", since = "1.0.0")]
364 unsafe impl<#[may_dangle] T: ?Sized> Drop for Mutex<T> {
366 // This is actually safe b/c we know that there is no further usage of
367 // this mutex (it's up to the user to arrange for a mutex to get
368 // dropped, that's not our job)
370 // IMPORTANT: This code must be kept in sync with `Mutex::into_inner`.
371 unsafe { self.inner.destroy() }
375 #[stable(feature = "mutex_default", since = "1.10.0")]
376 impl<T: ?Sized + Default> Default for Mutex<T> {
377 /// Creates a `Mutex<T>`, with the `Default` value for T.
378 fn default() -> Mutex<T> {
379 Mutex::new(Default::default())
383 #[stable(feature = "rust1", since = "1.0.0")]
384 impl<T: ?Sized + fmt::Debug> fmt::Debug for Mutex<T> {
385 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
386 match self.try_lock() {
387 Ok(guard) => write!(f, "Mutex {{ data: {:?} }}", &*guard),
388 Err(TryLockError::Poisoned(err)) => {
389 write!(f, "Mutex {{ data: Poisoned({:?}) }}", &**err.get_ref())
391 Err(TryLockError::WouldBlock) => write!(f, "Mutex {{ <locked> }}")
396 impl<'mutex, T: ?Sized> MutexGuard<'mutex, T> {
397 unsafe fn new(lock: &'mutex Mutex<T>) -> LockResult<MutexGuard<'mutex, T>> {
398 poison::map_result(lock.poison.borrow(), |guard| {
407 #[stable(feature = "rust1", since = "1.0.0")]
408 impl<'mutex, T: ?Sized> Deref for MutexGuard<'mutex, T> {
411 fn deref(&self) -> &T {
412 unsafe { &*self.__lock.data.get() }
416 #[stable(feature = "rust1", since = "1.0.0")]
417 impl<'mutex, T: ?Sized> DerefMut for MutexGuard<'mutex, T> {
418 fn deref_mut(&mut self) -> &mut T {
419 unsafe { &mut *self.__lock.data.get() }
423 #[stable(feature = "rust1", since = "1.0.0")]
424 impl<'a, T: ?Sized> Drop for MutexGuard<'a, T> {
428 self.__lock.poison.done(&self.__poison);
429 self.__lock.inner.unlock();
434 #[stable(feature = "std_debug", since = "1.16.0")]
435 impl<'a, T: ?Sized + fmt::Debug> fmt::Debug for MutexGuard<'a, T> {
436 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
437 f.debug_struct("MutexGuard")
438 .field("lock", &self.__lock)
443 pub fn guard_lock<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a sys::Mutex {
447 pub fn guard_poison<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a poison::Flag {
451 #[cfg(all(test, not(target_os = "emscripten")))]
453 use sync::mpsc::channel;
454 use sync::{Arc, Mutex, Condvar};
455 use sync::atomic::{AtomicUsize, Ordering};
458 struct Packet<T>(Arc<(Mutex<T>, Condvar)>);
460 #[derive(Eq, PartialEq, Debug)]
465 let m = Mutex::new(());
466 drop(m.lock().unwrap());
467 drop(m.lock().unwrap());
475 let m = Arc::new(Mutex::new(0));
477 fn inc(m: &Mutex<u32>) {
479 *m.lock().unwrap() += 1;
483 let (tx, rx) = channel();
485 let tx2 = tx.clone();
487 thread::spawn(move|| { inc(&m2); tx2.send(()).unwrap(); });
488 let tx2 = tx.clone();
490 thread::spawn(move|| { inc(&m2); tx2.send(()).unwrap(); });
497 assert_eq!(*m.lock().unwrap(), J * K * 2);
502 let m = Mutex::new(());
503 *m.try_lock().unwrap() = ();
507 fn test_into_inner() {
508 let m = Mutex::new(NonCopy(10));
509 assert_eq!(m.into_inner().unwrap(), NonCopy(10));
513 fn test_into_inner_drop() {
514 struct Foo(Arc<AtomicUsize>);
517 self.0.fetch_add(1, Ordering::SeqCst);
520 let num_drops = Arc::new(AtomicUsize::new(0));
521 let m = Mutex::new(Foo(num_drops.clone()));
522 assert_eq!(num_drops.load(Ordering::SeqCst), 0);
524 let _inner = m.into_inner().unwrap();
525 assert_eq!(num_drops.load(Ordering::SeqCst), 0);
527 assert_eq!(num_drops.load(Ordering::SeqCst), 1);
531 fn test_into_inner_poison() {
532 let m = Arc::new(Mutex::new(NonCopy(10)));
534 let _ = thread::spawn(move || {
535 let _lock = m2.lock().unwrap();
536 panic!("test panic in inner thread to poison mutex");
539 assert!(m.is_poisoned());
540 match Arc::try_unwrap(m).unwrap().into_inner() {
541 Err(e) => assert_eq!(e.into_inner(), NonCopy(10)),
542 Ok(x) => panic!("into_inner of poisoned Mutex is Ok: {:?}", x),
548 let mut m = Mutex::new(NonCopy(10));
549 *m.get_mut().unwrap() = NonCopy(20);
550 assert_eq!(m.into_inner().unwrap(), NonCopy(20));
554 fn test_get_mut_poison() {
555 let m = Arc::new(Mutex::new(NonCopy(10)));
557 let _ = thread::spawn(move || {
558 let _lock = m2.lock().unwrap();
559 panic!("test panic in inner thread to poison mutex");
562 assert!(m.is_poisoned());
563 match Arc::try_unwrap(m).unwrap().get_mut() {
564 Err(e) => assert_eq!(*e.into_inner(), NonCopy(10)),
565 Ok(x) => panic!("get_mut of poisoned Mutex is Ok: {:?}", x),
570 fn test_mutex_arc_condvar() {
571 let packet = Packet(Arc::new((Mutex::new(false), Condvar::new())));
572 let packet2 = Packet(packet.0.clone());
573 let (tx, rx) = channel();
574 let _t = thread::spawn(move|| {
575 // wait until parent gets in
577 let &(ref lock, ref cvar) = &*packet2.0;
578 let mut lock = lock.lock().unwrap();
583 let &(ref lock, ref cvar) = &*packet.0;
584 let mut lock = lock.lock().unwrap();
585 tx.send(()).unwrap();
588 lock = cvar.wait(lock).unwrap();
593 fn test_arc_condvar_poison() {
594 let packet = Packet(Arc::new((Mutex::new(1), Condvar::new())));
595 let packet2 = Packet(packet.0.clone());
596 let (tx, rx) = channel();
598 let _t = thread::spawn(move || -> () {
600 let &(ref lock, ref cvar) = &*packet2.0;
601 let _g = lock.lock().unwrap();
603 // Parent should fail when it wakes up.
607 let &(ref lock, ref cvar) = &*packet.0;
608 let mut lock = lock.lock().unwrap();
609 tx.send(()).unwrap();
611 match cvar.wait(lock) {
614 assert_eq!(*lock, 1);
622 fn test_mutex_arc_poison() {
623 let arc = Arc::new(Mutex::new(1));
624 assert!(!arc.is_poisoned());
625 let arc2 = arc.clone();
626 let _ = thread::spawn(move|| {
627 let lock = arc2.lock().unwrap();
628 assert_eq!(*lock, 2);
630 assert!(arc.lock().is_err());
631 assert!(arc.is_poisoned());
635 fn test_mutex_arc_nested() {
636 // Tests nested mutexes and access
637 // to underlying data.
638 let arc = Arc::new(Mutex::new(1));
639 let arc2 = Arc::new(Mutex::new(arc));
640 let (tx, rx) = channel();
641 let _t = thread::spawn(move|| {
642 let lock = arc2.lock().unwrap();
643 let lock2 = lock.lock().unwrap();
644 assert_eq!(*lock2, 1);
645 tx.send(()).unwrap();
651 fn test_mutex_arc_access_in_unwind() {
652 let arc = Arc::new(Mutex::new(1));
653 let arc2 = arc.clone();
654 let _ = thread::spawn(move|| -> () {
658 impl Drop for Unwinder {
660 *self.i.lock().unwrap() += 1;
663 let _u = Unwinder { i: arc2 };
666 let lock = arc.lock().unwrap();
667 assert_eq!(*lock, 2);
671 fn test_mutex_unsized() {
672 let mutex: &Mutex<[i32]> = &Mutex::new([1, 2, 3]);
674 let b = &mut *mutex.lock().unwrap();
678 let comp: &[i32] = &[4, 2, 5];
679 assert_eq!(&*mutex.lock().unwrap(), comp);