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>,
116 __marker: marker::NoSend,
119 /// RAII structure used to release the exclusive write access of a lock when
123 pub struct RwLockWriteGuard<'a, T: 'a> {
124 __lock: &'a StaticRwLock,
125 __data: &'a UnsafeCell<T>,
126 __poison: poison::Guard,
127 __marker: marker::NoSend,
130 impl<T: Send + Sync> RwLock<T> {
131 /// Creates a new instance of an RwLock which is unlocked and read to go.
133 pub fn new(t: T) -> RwLock<T> {
134 RwLock { inner: box RW_LOCK_INIT, data: UnsafeCell::new(t) }
137 /// Locks this rwlock with shared read access, blocking the current thread
138 /// until it can be acquired.
140 /// The calling thread will be blocked until there are no more writers which
141 /// hold the lock. There may be other readers currently inside the lock when
142 /// this method returns. This method does not provide any guarantees with
143 /// respect to the ordering of whether contentious readers or writers will
144 /// acquire the lock first.
146 /// Returns an RAII guard which will release this thread's shared access
147 /// once it is dropped.
151 /// This function will return an error if the RwLock is poisoned. An RwLock
152 /// is poisoned whenever a writer panics while holding an exclusive lock.
153 /// The failure will occur immediately after the lock has been acquired.
156 pub fn read(&self) -> LockResult<RwLockReadGuard<T>> {
157 unsafe { self.inner.lock.read() }
158 RwLockReadGuard::new(&*self.inner, &self.data)
161 /// Attempt to acquire this lock with shared read access.
163 /// This function will never block and will return immediately if `read`
164 /// would otherwise succeed. Returns `Some` of an RAII guard which will
165 /// release the shared access of this thread when dropped, or `None` if the
166 /// access could not be granted. This method does not provide any
167 /// guarantees with respect to the ordering of whether contentious readers
168 /// or writers will acquire the lock first.
172 /// This function will return an error if the RwLock is poisoned. An RwLock
173 /// is poisoned whenever a writer panics while holding an exclusive lock. An
174 /// error will only be returned if the lock would have otherwise been
178 pub fn try_read(&self) -> TryLockResult<RwLockReadGuard<T>> {
179 if unsafe { self.inner.lock.try_read() } {
180 Ok(try!(RwLockReadGuard::new(&*self.inner, &self.data)))
182 Err(TryLockError::WouldBlock)
186 /// Lock this rwlock with exclusive write access, blocking the current
187 /// thread until it can be acquired.
189 /// This function will not return while other writers or other readers
190 /// currently have access to the lock.
192 /// Returns an RAII guard which will drop the write access of this rwlock
197 /// This function will return an error if the RwLock is poisoned. An RwLock
198 /// is poisoned whenever a writer panics while holding an exclusive lock.
199 /// An error will be returned when the lock is acquired.
202 pub fn write(&self) -> LockResult<RwLockWriteGuard<T>> {
203 unsafe { self.inner.lock.write() }
204 RwLockWriteGuard::new(&*self.inner, &self.data)
207 /// Attempt to lock this rwlock with exclusive write access.
209 /// This function does not ever block, and it will return `None` if a call
210 /// to `write` would otherwise block. If successful, an RAII guard is
215 /// This function will return an error if the RwLock is poisoned. An RwLock
216 /// is poisoned whenever a writer panics while holding an exclusive lock. An
217 /// error will only be returned if the lock would have otherwise been
221 pub fn try_write(&self) -> TryLockResult<RwLockWriteGuard<T>> {
222 if unsafe { self.inner.lock.try_read() } {
223 Ok(try!(RwLockWriteGuard::new(&*self.inner, &self.data)))
225 Err(TryLockError::WouldBlock)
232 impl<T> Drop for RwLock<T> {
234 unsafe { self.inner.lock.destroy() }
238 struct Dummy(UnsafeCell<()>);
239 unsafe impl Sync for Dummy {}
240 static DUMMY: Dummy = Dummy(UnsafeCell { value: () });
243 /// Locks this rwlock with shared read access, blocking the current thread
244 /// until it can be acquired.
246 /// See `RwLock::read`.
248 #[unstable = "may be merged with RwLock in the future"]
249 pub fn read(&'static self) -> LockResult<RwLockReadGuard<'static, ()>> {
250 unsafe { self.lock.read() }
251 RwLockReadGuard::new(self, &DUMMY.0)
254 /// Attempt to acquire this lock with shared read access.
256 /// See `RwLock::try_read`.
258 #[unstable = "may be merged with RwLock in the future"]
259 pub fn try_read(&'static self)
260 -> TryLockResult<RwLockReadGuard<'static, ()>> {
261 if unsafe { self.lock.try_read() } {
262 Ok(try!(RwLockReadGuard::new(self, &DUMMY.0)))
264 Err(TryLockError::WouldBlock)
268 /// Lock this rwlock with exclusive write access, blocking the current
269 /// thread until it can be acquired.
271 /// See `RwLock::write`.
273 #[unstable = "may be merged with RwLock in the future"]
274 pub fn write(&'static self) -> LockResult<RwLockWriteGuard<'static, ()>> {
275 unsafe { self.lock.write() }
276 RwLockWriteGuard::new(self, &DUMMY.0)
279 /// Attempt to lock this rwlock with exclusive write access.
281 /// See `RwLock::try_write`.
283 #[unstable = "may be merged with RwLock in the future"]
284 pub fn try_write(&'static self)
285 -> TryLockResult<RwLockWriteGuard<'static, ()>> {
286 if unsafe { self.lock.try_write() } {
287 Ok(try!(RwLockWriteGuard::new(self, &DUMMY.0)))
289 Err(TryLockError::WouldBlock)
293 /// Deallocate all resources associated with this static lock.
295 /// This method is unsafe to call as there is no guarantee that there are no
296 /// active users of the lock, and this also doesn't prevent any future users
297 /// of this lock. This method is required to be called to not leak memory on
299 #[unstable = "may be merged with RwLock in the future"]
300 pub unsafe fn destroy(&'static self) {
305 impl<'rwlock, T> RwLockReadGuard<'rwlock, T> {
306 fn new(lock: &'rwlock StaticRwLock, data: &'rwlock UnsafeCell<T>)
307 -> LockResult<RwLockReadGuard<'rwlock, T>> {
308 poison::map_result(lock.poison.borrow(), |_| {
312 __marker: marker::NoSend,
317 impl<'rwlock, T> RwLockWriteGuard<'rwlock, T> {
318 fn new(lock: &'rwlock StaticRwLock, data: &'rwlock UnsafeCell<T>)
319 -> LockResult<RwLockWriteGuard<'rwlock, T>> {
320 poison::map_result(lock.poison.borrow(), |guard| {
325 __marker: marker::NoSend,
332 impl<'rwlock, T> Deref for RwLockReadGuard<'rwlock, T> {
335 fn deref(&self) -> &T { unsafe { &*self.__data.get() } }
338 impl<'rwlock, T> Deref for RwLockWriteGuard<'rwlock, T> {
341 fn deref(&self) -> &T { unsafe { &*self.__data.get() } }
344 impl<'rwlock, T> DerefMut for RwLockWriteGuard<'rwlock, T> {
345 fn deref_mut(&mut self) -> &mut T {
346 unsafe { &mut *self.__data.get() }
352 impl<'a, T> Drop for RwLockReadGuard<'a, T> {
354 unsafe { self.__lock.lock.read_unlock(); }
360 impl<'a, T> Drop for RwLockWriteGuard<'a, T> {
362 self.__lock.poison.done(&self.__poison);
363 unsafe { self.__lock.lock.write_unlock(); }
371 use rand::{self, Rng};
372 use sync::mpsc::channel;
374 use sync::{Arc, RwLock, StaticRwLock, RW_LOCK_INIT};
378 let l = RwLock::new(());
379 drop(l.read().unwrap());
380 drop(l.write().unwrap());
381 drop((l.read().unwrap(), l.read().unwrap()));
382 drop(l.write().unwrap());
387 static R: StaticRwLock = RW_LOCK_INIT;
388 drop(R.read().unwrap());
389 drop(R.write().unwrap());
390 drop((R.read().unwrap(), R.read().unwrap()));
391 drop(R.write().unwrap());
392 unsafe { R.destroy(); }
397 static R: StaticRwLock = RW_LOCK_INIT;
399 static M: uint = 1000;
401 let (tx, rx) = channel::<()>();
402 for _ in range(0, N) {
404 Thread::spawn(move|| {
405 let mut rng = rand::thread_rng();
406 for _ in range(0, M) {
407 if rng.gen_weighted_bool(N) {
408 drop(R.write().unwrap());
410 drop(R.read().unwrap());
418 unsafe { R.destroy(); }
422 fn test_rw_arc_poison_wr() {
423 let arc = Arc::new(RwLock::new(1i));
424 let arc2 = arc.clone();
425 let _: Result<uint, _> = Thread::spawn(move|| {
426 let _lock = arc2.write().unwrap();
429 assert!(arc.read().is_err());
433 fn test_rw_arc_poison_ww() {
434 let arc = Arc::new(RwLock::new(1i));
435 let arc2 = arc.clone();
436 let _: Result<uint, _> = Thread::spawn(move|| {
437 let _lock = arc2.write().unwrap();
440 assert!(arc.write().is_err());
444 fn test_rw_arc_no_poison_rr() {
445 let arc = Arc::new(RwLock::new(1i));
446 let arc2 = arc.clone();
447 let _: Result<uint, _> = Thread::spawn(move|| {
448 let _lock = arc2.read().unwrap();
451 let lock = arc.read().unwrap();
452 assert_eq!(*lock, 1);
455 fn test_rw_arc_no_poison_rw() {
456 let arc = Arc::new(RwLock::new(1i));
457 let arc2 = arc.clone();
458 let _: Result<uint, _> = Thread::spawn(move|| {
459 let _lock = arc2.read().unwrap();
462 let lock = arc.write().unwrap();
463 assert_eq!(*lock, 1);
468 let arc = Arc::new(RwLock::new(0i));
469 let arc2 = arc.clone();
470 let (tx, rx) = channel();
472 Thread::spawn(move|| {
473 let mut lock = arc2.write().unwrap();
474 for _ in range(0u, 10) {
480 tx.send(()).unwrap();
483 // Readers try to catch the writer in the act
484 let mut children = Vec::new();
485 for _ in range(0u, 5) {
486 let arc3 = arc.clone();
487 children.push(Thread::spawn(move|| {
488 let lock = arc3.read().unwrap();
493 // Wait for children to pass their asserts
494 for r in children.into_iter() {
495 assert!(r.join().is_ok());
498 // Wait for writer to finish
500 let lock = arc.read().unwrap();
501 assert_eq!(*lock, 10);
505 fn test_rw_arc_access_in_unwind() {
506 let arc = Arc::new(RwLock::new(1i));
507 let arc2 = arc.clone();
508 let _ = Thread::spawn(move|| -> () {
512 impl Drop for Unwinder {
514 let mut lock = self.i.write().unwrap();
518 let _u = Unwinder { i: arc2 };
521 let lock = arc.read().unwrap();
522 assert_eq!(*lock, 2);