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.
15 use ops::{Deref, DerefMut};
16 use sync::poison::{self, LockResult, TryLockError, TryLockResult};
17 use sys_common::rwlock as sys;
19 /// A reader-writer lock
21 /// This type of lock allows a number of readers or at most one writer at any
22 /// point in time. The write portion of this lock typically allows modification
23 /// of the underlying data (exclusive access) and the read portion of this lock
24 /// typically allows for read-only access (shared access).
26 /// The type parameter `T` represents the data that this lock protects. It is
27 /// required that `T` satisfies `Send` to be shared across tasks and `Sync` to
28 /// allow concurrent access through readers. The RAII guards returned from the
29 /// locking methods implement `Deref` (and `DerefMut` for the `write` methods)
30 /// to allow access to the contained of the lock.
34 /// RwLocks, like Mutexes, will become poisoned on panics. Note, however, that
35 /// an RwLock may only be poisoned if a panic occurs while it is locked
36 /// exclusively (write mode). If a panic occurs in any reader, then the lock
37 /// will not be poisoned.
42 /// use std::sync::RwLock;
44 /// let lock = RwLock::new(5i);
46 /// // many reader locks can be held at once
48 /// let r1 = lock.read().unwrap();
49 /// let r2 = lock.read().unwrap();
50 /// assert_eq!(*r1, 5);
51 /// assert_eq!(*r2, 5);
52 /// } // read locks are dropped at this point
54 /// // only one write lock may be held, however
56 /// let mut w = lock.write().unwrap();
58 /// assert_eq!(*w, 6);
59 /// } // write lock is dropped here
62 pub struct RwLock<T> {
63 inner: Box<StaticRwLock>,
67 unsafe impl<T:'static+Send> Send for RwLock<T> {}
68 unsafe impl<T> Sync for RwLock<T> {}
70 /// Structure representing a statically allocated RwLock.
72 /// This structure is intended to be used inside of a `static` and will provide
73 /// automatic global access as well as lazy initialization. The internal
74 /// resources of this RwLock, however, must be manually deallocated.
79 /// use std::sync::{StaticRwLock, RW_LOCK_INIT};
81 /// static LOCK: StaticRwLock = RW_LOCK_INIT;
84 /// let _g = LOCK.read().unwrap();
85 /// // ... shared read access
88 /// let _g = LOCK.write().unwrap();
89 /// // ... exclusive write access
91 /// unsafe { LOCK.destroy() } // free all resources
93 #[unstable = "may be merged with RwLock in the future"]
94 pub struct StaticRwLock {
99 unsafe impl Send for StaticRwLock {}
100 unsafe impl Sync for StaticRwLock {}
102 /// Constant initialization for a statically-initialized rwlock.
103 #[unstable = "may be merged with RwLock in the future"]
104 pub const RW_LOCK_INIT: StaticRwLock = StaticRwLock {
105 lock: sys::RWLOCK_INIT,
106 poison: poison::FLAG_INIT,
109 /// RAII structure used to release the shared read access of a lock when
113 pub struct RwLockReadGuard<'a, T: 'a> {
114 __lock: &'a StaticRwLock,
115 __data: &'a UnsafeCell<T>,
118 impl<'a, T> !marker::Send for RwLockReadGuard<'a, T> {}
120 /// RAII structure used to release the exclusive write access of a lock when
124 pub struct RwLockWriteGuard<'a, T: 'a> {
125 __lock: &'a StaticRwLock,
126 __data: &'a UnsafeCell<T>,
127 __poison: poison::Guard,
130 impl<'a, T> !marker::Send for RwLockWriteGuard<'a, T> {}
132 impl<T: Send + Sync> RwLock<T> {
133 /// Creates a new instance of an RwLock which is unlocked and read to go.
135 pub fn new(t: T) -> RwLock<T> {
136 RwLock { inner: box RW_LOCK_INIT, data: UnsafeCell::new(t) }
139 /// Locks this rwlock with shared read access, blocking the current thread
140 /// until it can be acquired.
142 /// The calling thread will be blocked until there are no more writers which
143 /// hold the lock. There may be other readers currently inside the lock when
144 /// this method returns. This method does not provide any guarantees with
145 /// respect to the ordering of whether contentious readers or writers will
146 /// acquire the lock first.
148 /// Returns an RAII guard which will release this thread's shared access
149 /// once it is dropped.
153 /// This function will return an error if the RwLock is poisoned. An RwLock
154 /// is poisoned whenever a writer panics while holding an exclusive lock.
155 /// The failure will occur immediately after the lock has been acquired.
158 pub fn read(&self) -> LockResult<RwLockReadGuard<T>> {
159 unsafe { self.inner.lock.read() }
160 RwLockReadGuard::new(&*self.inner, &self.data)
163 /// Attempt to acquire this lock with shared read access.
165 /// This function will never block and will return immediately if `read`
166 /// would otherwise succeed. Returns `Some` of an RAII guard which will
167 /// release the shared access of this thread when dropped, or `None` if the
168 /// access could not be granted. This method does not provide any
169 /// guarantees with respect to the ordering of whether contentious readers
170 /// or writers will acquire the lock first.
174 /// This function will return an error if the RwLock is poisoned. An RwLock
175 /// is poisoned whenever a writer panics while holding an exclusive lock. An
176 /// error will only be returned if the lock would have otherwise been
180 pub fn try_read(&self) -> TryLockResult<RwLockReadGuard<T>> {
181 if unsafe { self.inner.lock.try_read() } {
182 Ok(try!(RwLockReadGuard::new(&*self.inner, &self.data)))
184 Err(TryLockError::WouldBlock)
188 /// Lock this rwlock with exclusive write access, blocking the current
189 /// thread until it can be acquired.
191 /// This function will not return while other writers or other readers
192 /// currently have access to the lock.
194 /// Returns an RAII guard which will drop the write access of this rwlock
199 /// This function will return an error if the RwLock is poisoned. An RwLock
200 /// is poisoned whenever a writer panics while holding an exclusive lock.
201 /// An error will be returned when the lock is acquired.
204 pub fn write(&self) -> LockResult<RwLockWriteGuard<T>> {
205 unsafe { self.inner.lock.write() }
206 RwLockWriteGuard::new(&*self.inner, &self.data)
209 /// Attempt to lock this rwlock with exclusive write access.
211 /// This function does not ever block, and it will return `None` if a call
212 /// to `write` would otherwise block. If successful, an RAII guard is
217 /// This function will return an error if the RwLock is poisoned. An RwLock
218 /// is poisoned whenever a writer panics while holding an exclusive lock. An
219 /// error will only be returned if the lock would have otherwise been
223 pub fn try_write(&self) -> TryLockResult<RwLockWriteGuard<T>> {
224 if unsafe { self.inner.lock.try_read() } {
225 Ok(try!(RwLockWriteGuard::new(&*self.inner, &self.data)))
227 Err(TryLockError::WouldBlock)
234 impl<T> Drop for RwLock<T> {
236 unsafe { self.inner.lock.destroy() }
240 struct Dummy(UnsafeCell<()>);
241 unsafe impl Sync for Dummy {}
242 static DUMMY: Dummy = Dummy(UnsafeCell { value: () });
245 /// Locks this rwlock with shared read access, blocking the current thread
246 /// until it can be acquired.
248 /// See `RwLock::read`.
250 #[unstable = "may be merged with RwLock in the future"]
251 pub fn read(&'static self) -> LockResult<RwLockReadGuard<'static, ()>> {
252 unsafe { self.lock.read() }
253 RwLockReadGuard::new(self, &DUMMY.0)
256 /// Attempt to acquire this lock with shared read access.
258 /// See `RwLock::try_read`.
260 #[unstable = "may be merged with RwLock in the future"]
261 pub fn try_read(&'static self)
262 -> TryLockResult<RwLockReadGuard<'static, ()>> {
263 if unsafe { self.lock.try_read() } {
264 Ok(try!(RwLockReadGuard::new(self, &DUMMY.0)))
266 Err(TryLockError::WouldBlock)
270 /// Lock this rwlock with exclusive write access, blocking the current
271 /// thread until it can be acquired.
273 /// See `RwLock::write`.
275 #[unstable = "may be merged with RwLock in the future"]
276 pub fn write(&'static self) -> LockResult<RwLockWriteGuard<'static, ()>> {
277 unsafe { self.lock.write() }
278 RwLockWriteGuard::new(self, &DUMMY.0)
281 /// Attempt to lock this rwlock with exclusive write access.
283 /// See `RwLock::try_write`.
285 #[unstable = "may be merged with RwLock in the future"]
286 pub fn try_write(&'static self)
287 -> TryLockResult<RwLockWriteGuard<'static, ()>> {
288 if unsafe { self.lock.try_write() } {
289 Ok(try!(RwLockWriteGuard::new(self, &DUMMY.0)))
291 Err(TryLockError::WouldBlock)
295 /// Deallocate all resources associated with this static lock.
297 /// This method is unsafe to call as there is no guarantee that there are no
298 /// active users of the lock, and this also doesn't prevent any future users
299 /// of this lock. This method is required to be called to not leak memory on
301 #[unstable = "may be merged with RwLock in the future"]
302 pub unsafe fn destroy(&'static self) {
307 impl<'rwlock, T> RwLockReadGuard<'rwlock, T> {
309 fn new(lock: &'rwlock StaticRwLock, data: &'rwlock UnsafeCell<T>)
310 -> LockResult<RwLockReadGuard<'rwlock, T>> {
311 poison::map_result(lock.poison.borrow(), |_| {
319 impl<'rwlock, T> RwLockWriteGuard<'rwlock, T> {
321 fn new(lock: &'rwlock StaticRwLock, data: &'rwlock UnsafeCell<T>)
322 -> LockResult<RwLockWriteGuard<'rwlock, T>> {
323 poison::map_result(lock.poison.borrow(), |guard| {
334 impl<'rwlock, T> Deref for RwLockReadGuard<'rwlock, T> {
337 fn deref(&self) -> &T { unsafe { &*self.__data.get() } }
340 impl<'rwlock, T> Deref for RwLockWriteGuard<'rwlock, T> {
343 fn deref(&self) -> &T { unsafe { &*self.__data.get() } }
346 impl<'rwlock, T> DerefMut for RwLockWriteGuard<'rwlock, T> {
347 fn deref_mut(&mut self) -> &mut T {
348 unsafe { &mut *self.__data.get() }
354 impl<'a, T> Drop for RwLockReadGuard<'a, T> {
356 unsafe { self.__lock.lock.read_unlock(); }
362 impl<'a, T> Drop for RwLockWriteGuard<'a, T> {
364 self.__lock.poison.done(&self.__poison);
365 unsafe { self.__lock.lock.write_unlock(); }
373 use rand::{self, Rng};
374 use sync::mpsc::channel;
376 use sync::{Arc, RwLock, StaticRwLock, RW_LOCK_INIT};
380 let l = RwLock::new(());
381 drop(l.read().unwrap());
382 drop(l.write().unwrap());
383 drop((l.read().unwrap(), l.read().unwrap()));
384 drop(l.write().unwrap());
389 static R: StaticRwLock = RW_LOCK_INIT;
390 drop(R.read().unwrap());
391 drop(R.write().unwrap());
392 drop((R.read().unwrap(), R.read().unwrap()));
393 drop(R.write().unwrap());
394 unsafe { R.destroy(); }
399 static R: StaticRwLock = RW_LOCK_INIT;
401 static M: uint = 1000;
403 let (tx, rx) = channel::<()>();
404 for _ in range(0, N) {
406 Thread::spawn(move|| {
407 let mut rng = rand::thread_rng();
408 for _ in range(0, M) {
409 if rng.gen_weighted_bool(N) {
410 drop(R.write().unwrap());
412 drop(R.read().unwrap());
420 unsafe { R.destroy(); }
424 fn test_rw_arc_poison_wr() {
425 let arc = Arc::new(RwLock::new(1i));
426 let arc2 = arc.clone();
427 let _: Result<uint, _> = Thread::scoped(move|| {
428 let _lock = arc2.write().unwrap();
431 assert!(arc.read().is_err());
435 fn test_rw_arc_poison_ww() {
436 let arc = Arc::new(RwLock::new(1i));
437 let arc2 = arc.clone();
438 let _: Result<uint, _> = Thread::scoped(move|| {
439 let _lock = arc2.write().unwrap();
442 assert!(arc.write().is_err());
446 fn test_rw_arc_no_poison_rr() {
447 let arc = Arc::new(RwLock::new(1i));
448 let arc2 = arc.clone();
449 let _: Result<uint, _> = Thread::scoped(move|| {
450 let _lock = arc2.read().unwrap();
453 let lock = arc.read().unwrap();
454 assert_eq!(*lock, 1);
457 fn test_rw_arc_no_poison_rw() {
458 let arc = Arc::new(RwLock::new(1i));
459 let arc2 = arc.clone();
460 let _: Result<uint, _> = Thread::scoped(move|| {
461 let _lock = arc2.read().unwrap();
464 let lock = arc.write().unwrap();
465 assert_eq!(*lock, 1);
470 let arc = Arc::new(RwLock::new(0i));
471 let arc2 = arc.clone();
472 let (tx, rx) = channel();
474 Thread::spawn(move|| {
475 let mut lock = arc2.write().unwrap();
476 for _ in range(0u, 10) {
482 tx.send(()).unwrap();
485 // Readers try to catch the writer in the act
486 let mut children = Vec::new();
487 for _ in range(0u, 5) {
488 let arc3 = arc.clone();
489 children.push(Thread::scoped(move|| {
490 let lock = arc3.read().unwrap();
495 // Wait for children to pass their asserts
496 for r in children.into_iter() {
497 assert!(r.join().is_ok());
500 // Wait for writer to finish
502 let lock = arc.read().unwrap();
503 assert_eq!(*lock, 10);
507 fn test_rw_arc_access_in_unwind() {
508 let arc = Arc::new(RwLock::new(1i));
509 let arc2 = arc.clone();
510 let _ = Thread::scoped(move|| -> () {
514 impl Drop for Unwinder {
516 let mut lock = self.i.write().unwrap();
520 let _u = Unwinder { i: arc2 };
523 let lock = arc.read().unwrap();
524 assert_eq!(*lock, 2);