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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.
4 //
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.
10
11 use prelude::v1::*;
12
13 use fmt;
14 use marker;
15 use ops::Deref;
16 use sys_common::poison::{self, TryLockError, TryLockResult, LockResult};
17 use sys::mutex as sys;
18
19 /// A re-entrant mutual exclusion
20 ///
21 /// This mutex will block *other* threads waiting for the lock to become
22 /// available. The thread which has already locked the mutex can lock it
23 /// multiple times without blocking, preventing a common source of deadlocks.
24 pub struct ReentrantMutex<T> {
25 inner: Box<sys::ReentrantMutex>,
26 poison: poison::Flag,
27 data: T,
28 }
29
30 unsafe impl<T: Send> Send for ReentrantMutex<T> {}
31 unsafe impl<T: Send> Sync for ReentrantMutex<T> {}
32
33
34 /// An RAII implementation of a "scoped lock" of a mutex. When this structure is
35 /// dropped (falls out of scope), the lock will be unlocked.
36 ///
37 /// The data protected by the mutex can be accessed through this guard via its
38 /// Deref implementation.
39 ///
40 /// # Mutability
41 ///
42 /// Unlike `MutexGuard`, `ReentrantMutexGuard` does not implement `DerefMut`,
43 /// because implementation of the trait would violate Rust’s reference aliasing
44 /// rules. Use interior mutability (usually `RefCell`) in order to mutate the
45 /// guarded data.
46 #[must_use]
47 pub struct ReentrantMutexGuard<'a, T: 'a> {
48 // funny underscores due to how Deref currently works (it disregards field
49 // privacy).
50 __lock: &'a ReentrantMutex<T>,
51 __poison: poison::Guard,
52 }
53
54 impl<'a, T> !marker::Send for ReentrantMutexGuard<'a, T> {}
55
56
57 impl<T> ReentrantMutex<T> {
58 /// Creates a new reentrant mutex in an unlocked state.
59 pub fn new(t: T) -> ReentrantMutex<T> {
60 unsafe {
61 let mut mutex = ReentrantMutex {
62 inner: box sys::ReentrantMutex::uninitialized(),
63 poison: poison::Flag::new(),
64 data: t,
65 };
66 mutex.inner.init();
67 mutex
68 }
69 }
70
71 /// Acquires a mutex, blocking the current thread until it is able to do so.
72 ///
73 /// This function will block the caller until it is available to acquire the mutex.
74 /// Upon returning, the thread is the only thread with the mutex held. When the thread
75 /// calling this method already holds the lock, the call shall succeed without
76 /// blocking.
77 ///
78 /// # Errors
79 ///
80 /// If another user of this mutex panicked while holding the mutex, then
81 /// this call will return failure if the mutex would otherwise be
82 /// acquired.
83 pub fn lock(&self) -> LockResult<ReentrantMutexGuard<T>> {
84 unsafe { self.inner.lock() }
85 ReentrantMutexGuard::new(&self)
86 }
87
88 /// Attempts to acquire this lock.
89 ///
90 /// If the lock could not be acquired at this time, then `Err` is returned.
91 /// Otherwise, an RAII guard is returned.
92 ///
93 /// This function does not block.
94 ///
95 /// # Errors
96 ///
97 /// If another user of this mutex panicked while holding the mutex, then
98 /// this call will return failure if the mutex would otherwise be
99 /// acquired.
100 pub fn try_lock(&self) -> TryLockResult<ReentrantMutexGuard<T>> {
101 if unsafe { self.inner.try_lock() } {
102 Ok(ReentrantMutexGuard::new(&self)?)
103 } else {
104 Err(TryLockError::WouldBlock)
105 }
106 }
107 }
108
109 impl<T> Drop for ReentrantMutex<T> {
110 fn drop(&mut self) {
111 // This is actually safe b/c we know that there is no further usage of
112 // this mutex (it's up to the user to arrange for a mutex to get
113 // dropped, that's not our job)
114 unsafe { self.inner.destroy() }
115 }
116 }
117
118 impl<T: fmt::Debug + 'static> fmt::Debug for ReentrantMutex<T> {
119 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
120 match self.try_lock() {
121 Ok(guard) => write!(f, "ReentrantMutex {{ data: {:?} }}", &*guard),
122 Err(TryLockError::Poisoned(err)) => {
123 write!(f, "ReentrantMutex {{ data: Poisoned({:?}) }}", &**err.get_ref())
124 },
125 Err(TryLockError::WouldBlock) => write!(f, "ReentrantMutex {{ <locked> }}")
126 }
127 }
128 }
129
130 impl<'mutex, T> ReentrantMutexGuard<'mutex, T> {
131 fn new(lock: &'mutex ReentrantMutex<T>)
132 -> LockResult<ReentrantMutexGuard<'mutex, T>> {
133 poison::map_result(lock.poison.borrow(), |guard| {
134 ReentrantMutexGuard {
135 __lock: lock,
136 __poison: guard,
137 }
138 })
139 }
140 }
141
142 impl<'mutex, T> Deref for ReentrantMutexGuard<'mutex, T> {
143 type Target = T;
144
145 fn deref(&self) -> &T {
146 &self.__lock.data
147 }
148 }
149
150 impl<'a, T> Drop for ReentrantMutexGuard<'a, T> {
151 #[inline]
152 fn drop(&mut self) {
153 unsafe {
154 self.__lock.poison.done(&self.__poison);
155 self.__lock.inner.unlock();
156 }
157 }
158 }
159
160
161 #[cfg(test)]
162 mod tests {
163 use prelude::v1::*;
164 use sys_common::remutex::{ReentrantMutex, ReentrantMutexGuard};
165 use cell::RefCell;
166 use sync::Arc;
167 use thread;
168
169 #[test]
170 fn smoke() {
171 let m = ReentrantMutex::new(());
172 {
173 let a = m.lock().unwrap();
174 {
175 let b = m.lock().unwrap();
176 {
177 let c = m.lock().unwrap();
178 assert_eq!(*c, ());
179 }
180 assert_eq!(*b, ());
181 }
182 assert_eq!(*a, ());
183 }
184 }
185
186 #[test]
187 fn is_mutex() {
188 let m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
189 let m2 = m.clone();
190 let lock = m.lock().unwrap();
191 let child = thread::spawn(move || {
192 let lock = m2.lock().unwrap();
193 assert_eq!(*lock.borrow(), 4950);
194 });
195 for i in 0..100 {
196 let lock = m.lock().unwrap();
197 *lock.borrow_mut() += i;
198 }
199 drop(lock);
200 child.join().unwrap();
201 }
202
203 #[test]
204 fn trylock_works() {
205 let m = Arc::new(ReentrantMutex::new(()));
206 let m2 = m.clone();
207 let _lock = m.try_lock().unwrap();
208 let _lock2 = m.try_lock().unwrap();
209 thread::spawn(move || {
210 let lock = m2.try_lock();
211 assert!(lock.is_err());
212 }).join().unwrap();
213 let _lock3 = m.try_lock().unwrap();
214 }
215
216 pub struct Answer<'a>(pub ReentrantMutexGuard<'a, RefCell<u32>>);
217 impl<'a> Drop for Answer<'a> {
218 fn drop(&mut self) {
219 *self.0.borrow_mut() = 42;
220 }
221 }
222
223 #[test]
224 fn poison_works() {
225 let m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
226 let mc = m.clone();
227 let result = thread::spawn(move ||{
228 let lock = mc.lock().unwrap();
229 *lock.borrow_mut() = 1;
230 let lock2 = mc.lock().unwrap();
231 *lock.borrow_mut() = 2;
232 let _answer = Answer(lock2);
233 panic!("What the answer to my lifetimes dilemma is?");
234 }).join();
235 assert!(result.is_err());
236 let r = m.lock().err().unwrap().into_inner();
237 assert_eq!(*r.borrow(), 42);
238 }
239 }