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oxedyne/fe2o3/fe2o3_text/tests/annealer_corpus/parking_mutex.rs

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1// Copyright 2016 Amanieu d'Antras
2//
3// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
4// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
5// http://opensource.org/licenses/MIT>, at your option. This file may not be
6// copied, modified, or distributed except according to those terms.
7
8use crate::raw_mutex::RawMutex;
9
10/// A mutual exclusion primitive useful for protecting shared data
11///
12/// This mutex will block threads waiting for the lock to become available. The
13/// mutex can be statically initialized or created by the `new`
14/// constructor. Each mutex has a type parameter which represents the data that
15/// it is protecting. The data can only be accessed through the RAII guards
16/// returned from `lock` and `try_lock`, which guarantees that the data is only
17/// ever accessed when the mutex is locked.
18///
19/// # Fairness
20///
21/// A typical unfair lock can often end up in a situation where a single thread
22/// quickly acquires and releases the same mutex in succession, which can starve
23/// other threads waiting to acquire the mutex. While this improves throughput
24/// because it doesn't force a context switch when a thread tries to re-acquire
25/// a mutex it has just released, this can starve other threads.
26///
27/// This mutex uses [eventual fairness](https://trac.webkit.org/changeset/203350)
28/// to ensure that the lock will be fair on average without sacrificing
29/// throughput. This is done by forcing a fair unlock on average every 0.5ms,
30/// which will force the lock to go to the next thread waiting for the mutex.
31///
32/// Additionally, any critical section longer than 1ms will always use a fair
33/// unlock, which has a negligible impact on throughput considering the length
34/// of the critical section.
35///
36/// You can also force a fair unlock by calling `MutexGuard::unlock_fair` when
37/// unlocking a mutex instead of simply dropping the `MutexGuard`.
38///
39/// # Differences from the standard library `Mutex`
40///
41/// - No poisoning, the lock is released normally on panic.
42/// - Only requires 1 byte of space, whereas the standard library boxes the
43/// `Mutex` due to platform limitations.
44/// - Can be statically constructed.
45/// - Does not require any drop glue when dropped.
46/// - Inline fast path for the uncontended case.
47/// - Efficient handling of micro-contention using adaptive spinning.
48/// - Allows raw locking & unlocking without a guard.
49/// - Supports eventual fairness so that the mutex is fair on average.
50/// - Optionally allows making the mutex fair by calling `MutexGuard::unlock_fair`.
51///
52/// # Examples
53///
54/// ```
55/// use parking_lot::Mutex;
56/// use std::sync::{Arc, mpsc::channel};
57/// use std::thread;
58///
59/// const N: usize = 10;
60///
61/// // Spawn a few threads to increment a shared variable (non-atomically), and
62/// // let the main thread know once all increments are done.
63/// //
64/// // Here we're using an Arc to share memory among threads, and the data inside
65/// // the Arc is protected with a mutex.
66/// let data = Arc::new(Mutex::new(0));
67///
68/// let (tx, rx) = channel();
69/// for _ in 0..10 {
70/// let (data, tx) = (Arc::clone(&data), tx.clone());
71/// thread::spawn(move || {
72/// // The shared state can only be accessed once the lock is held.
73/// // Our non-atomic increment is safe because we're the only thread
74/// // which can access the shared state when the lock is held.
75/// let mut data = data.lock();
76/// *data += 1;
77/// if *data == N {
78/// tx.send(()).unwrap();
79/// }
80/// // the lock is unlocked here when `data` goes out of scope.
81/// });
82/// }
83///
84/// rx.recv().unwrap();
85/// ```
86pub type Mutex<T> = lock_api::Mutex<RawMutex, T>;
87
88/// Creates a new mutex in an unlocked state ready for use.
89///
90/// This allows creating a mutex in a constant context on stable Rust.
91pub const fn const_mutex<T>(val: T) -> Mutex<T> {
92 Mutex::const_new(<RawMutex as lock_api::RawMutex>::INIT, val)
93}
94
95/// An RAII implementation of a "scoped lock" of a mutex. When this structure is
96/// dropped (falls out of scope), the lock will be unlocked.
97///
98/// The data protected by the mutex can be accessed through this guard via its
99/// `Deref` and `DerefMut` implementations.
100pub type MutexGuard<'a, T> = lock_api::MutexGuard<'a, RawMutex, T>;
101
102/// An RAII mutex guard returned by `MutexGuard::map`, which can point to a
103/// subfield of the protected data.
104///
105/// The main difference between `MappedMutexGuard` and `MutexGuard` is that the
106/// former doesn't support temporarily unlocking and re-locking, since that
107/// could introduce soundness issues if the locked object is modified by another
108/// thread.
109pub type MappedMutexGuard<'a, T> = lock_api::MappedMutexGuard<'a, RawMutex, T>;
110
111#[cfg(test)]
112mod tests {
113 use crate::{Condvar, MappedMutexGuard, Mutex, MutexGuard};
114 use std::collections::HashMap;
115 use std::ops::Deref;
116 use std::sync::atomic::{AtomicUsize, Ordering};
117 use std::sync::mpsc::channel;
118 use std::sync::Arc;
119 use std::thread;
120
121 #[cfg(feature = "serde")]
122 use postcard::{from_bytes, to_stdvec};
123
124 struct Packet<T>(Arc<(Mutex<T>, Condvar)>);
125
126 #[derive(Eq, PartialEq, Debug)]
127 struct NonCopy(i32);
128
129 unsafe impl<T: Send> Send for Packet<T> {}
130 unsafe impl<T> Sync for Packet<T> {}
131
132 #[test]
133 fn smoke() {
134 let m = Mutex::new(());
135 drop(m.lock());
136 drop(m.lock());
137 }
138
139 #[test]
140 fn lots_and_lots() {
141 const J: u32 = if cfg!(miri) { 200 } else { 1000 };
142 const K: u32 = 3;
143
144 let m = Arc::new(Mutex::new(0));
145
146 fn inc(m: &Mutex<u32>) {
147 for _ in 0..J {
148 *m.lock() += 1;
149 }
150 }
151
152 let (tx, rx) = channel();
153 for _ in 0..K {
154 let tx2 = tx.clone();
155 let m2 = m.clone();
156 thread::spawn(move || {
157 inc(&m2);
158 tx2.send(()).unwrap();
159 });
160 let tx2 = tx.clone();
161 let m2 = m.clone();
162 thread::spawn(move || {
163 inc(&m2);
164 tx2.send(()).unwrap();
165 });
166 }
167
168 drop(tx);
169 for _ in 0..2 * K {
170 rx.recv().unwrap();
171 }
172 assert_eq!(*m.lock(), J * K * 2);
173 }
174
175 #[test]
176 fn try_lock() {
177 let m = Mutex::new(());
178 *m.try_lock().unwrap() = ();
179 }
180
181 #[test]
182 fn test_into_inner() {
183 let m = Mutex::new(NonCopy(10));
184 assert_eq!(m.into_inner(), NonCopy(10));
185 }
186
187 #[test]
188 fn test_into_inner_drop() {
189 struct Foo(Arc<AtomicUsize>);
190 impl Drop for Foo {
191 fn drop(&mut self) {
192 self.0.fetch_add(1, Ordering::SeqCst);
193 }
194 }
195 let num_drops = Arc::new(AtomicUsize::new(0));
196 let m = Mutex::new(Foo(num_drops.clone()));
197 assert_eq!(num_drops.load(Ordering::SeqCst), 0);
198 {
199 let _inner = m.into_inner();
200 assert_eq!(num_drops.load(Ordering::SeqCst), 0);
201 }
202 assert_eq!(num_drops.load(Ordering::SeqCst), 1);
203 }
204
205 #[test]
206 fn test_get_mut() {
207 let mut m = Mutex::new(NonCopy(10));
208 *m.get_mut() = NonCopy(20);
209 assert_eq!(m.into_inner(), NonCopy(20));
210 }
211
212 #[test]
213 fn test_mutex_arc_condvar() {
214 let packet = Packet(Arc::new((Mutex::new(false), Condvar::new())));
215 let packet2 = Packet(packet.0.clone());
216 let (tx, rx) = channel();
217 let _t = thread::spawn(move || {
218 // wait until parent gets in
219 rx.recv().unwrap();
220 let (lock, cvar) = &*packet2.0;
221 let mut lock = lock.lock();
222 *lock = true;
223 cvar.notify_one();
224 });
225
226 let (lock, cvar) = &*packet.0;
227 let mut lock = lock.lock();
228 tx.send(()).unwrap();
229 assert!(!*lock);
230 while !*lock {
231 cvar.wait(&mut lock);
232 }
233 }
234
235 #[test]
236 fn test_mutex_arc_nested() {
237 // Tests nested mutexes and access
238 // to underlying data.
239 let arc = Arc::new(Mutex::new(1));
240 let arc2 = Arc::new(Mutex::new(arc));
241 let (tx, rx) = channel();
242 let _t = thread::spawn(move || {
243 let lock = arc2.lock();
244 let lock2 = lock.lock();
245 assert_eq!(*lock2, 1);
246 tx.send(()).unwrap();
247 });
248 rx.recv().unwrap();
249 }
250
251 #[test]
252 fn test_mutex_arc_access_in_unwind() {
253 let arc = Arc::new(Mutex::new(1));
254 let arc2 = arc.clone();
255 let _ = thread::spawn(move || {
256 struct Unwinder {
257 i: Arc<Mutex<i32>>,
258 }
259 impl Drop for Unwinder {
260 fn drop(&mut self) {
261 *self.i.lock() += 1;
262 }
263 }
264 let _u = Unwinder { i: arc2 };
265 panic!();
266 })
267 .join();
268 let lock = arc.lock();
269 assert_eq!(*lock, 2);
270 }
271
272 #[test]
273 fn test_mutex_unsized() {
274 let mutex: &Mutex<[i32]> = &Mutex::new([1, 2, 3]);
275 {
276 let b = &mut *mutex.lock();
277 b[0] = 4;
278 b[2] = 5;
279 }
280 let comp: &[i32] = &[4, 2, 5];
281 assert_eq!(&*mutex.lock(), comp);
282 }
283
284 #[test]
285 fn test_mutexguard_sync() {
286 fn sync<T: Sync>(_: T) {}
287
288 let mutex = Mutex::new(());
289 sync(mutex.lock());
290 }
291
292 #[test]
293 fn test_mutex_debug() {
294 let mutex = Mutex::new(vec![0u8, 10]);
295
296 assert_eq!(format!("{:?}", mutex), "Mutex { data: [0, 10] }");
297 let _lock = mutex.lock();
298 assert_eq!(format!("{:?}", mutex), "Mutex { data: <locked> }");
299 }
300
301 #[cfg(feature = "serde")]
302 #[test]
303 fn test_serde() {
304 let contents: Vec<u8> = vec![0, 1, 2];
305 let mutex = Mutex::new(contents.clone());
306
307 let serialized = to_stdvec(&mutex).unwrap();
308 let deserialized: Mutex<Vec<u8>> = from_bytes(&serialized).unwrap();
309
310 assert_eq!(*(mutex.lock()), *(deserialized.lock()));
311 assert_eq!(contents, *(deserialized.lock()));
312 }
313
314 #[test]
315 fn test_map_or_err_not_mapped() {
316 let mut map = HashMap::new();
317 map.insert("hello".to_string(), "world".to_string());
318
319 let mutex = Mutex::new(map);
320 let guard = mutex.lock();
321 let guard = match MutexGuard::try_map_or_err(guard, |the_map| {
322 the_map.get_mut("hello2").ok_or(12345i32)
323 }) {
324 Ok(_) => unreachable!(),
325 Err((guard, data)) => {
326 assert_eq!(data, 12345i32);
327 assert_eq!(guard.get("hello"), Some(&"world".to_string()));
328 guard
329 }
330 };
331
332 // Lets try again
333 let mapped_guard = match MutexGuard::try_map_or_err(guard, |the_map| {
334 the_map.get_mut("hello").ok_or("unreachable")
335 }) {
336 Ok(mapped_guard) => mapped_guard,
337 Err((_, _)) => unreachable!(),
338 };
339
340 assert_eq!(mapped_guard.as_str(), "world");
341
342 match MappedMutexGuard::try_map_or_err(mapped_guard, |the_string| {
343 if the_string != "world" {
344 //unreachable
345 Ok(the_string.as_mut_str())
346 } else {
347 Err(45678i32)
348 }
349 }) {
350 Ok(_) => unreachable!(),
351 Err((guard, err)) => {
352 assert_eq!(guard.as_str(), "world");
353 assert_eq!(err, 45678i32);
354 }
355 };
356 }
357
358 #[test]
359 fn test_map_or_err_mapped() {
360 let mut map = HashMap::new();
361 map.insert("hello".to_string(), "world".to_string());
362
363 let mutex = Mutex::new(map);
364 let guard = mutex.lock();
365 let mapped_guard = match MutexGuard::try_map_or_err(guard, |the_map| {
366 the_map.get_mut("hello").ok_or("unreachable")
367 }) {
368 Ok(mapped_guard) => mapped_guard,
369 Err((_, _)) => unreachable!(),
370 };
371
372 assert_eq!(mapped_guard.as_str(), "world");
373
374 match MappedMutexGuard::try_map_or_err(mapped_guard, |the_string| {
375 if the_string == "world" {
376 Ok(the_string.as_mut_str())
377 } else {
378 Err("unreachable")
379 }
380 }) {
381 Ok(mapped_guard) => assert_eq!(mapped_guard.deref(), "world"),
382 Err((_, _)) => unreachable!(),
383 };
384 }
385}