parking_lot/
remutex.rs

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;
9use core::num::NonZeroUsize;
10use lock_api::{self, GetThreadId};
11
12/// Implementation of the `GetThreadId` trait for `lock_api::ReentrantMutex`.
13pub struct RawThreadId;
14
15unsafe impl GetThreadId for RawThreadId {
16    const INIT: RawThreadId = RawThreadId;
17
18    fn nonzero_thread_id(&self) -> NonZeroUsize {
19        // The address of a thread-local variable is guaranteed to be unique to the
20        // current thread, and is also guaranteed to be non-zero. The variable has to have a
21        // non-zero size to guarantee it has a unique address for each thread.
22        thread_local!(static KEY: u8 = 0);
23        KEY.with(|x| {
24            NonZeroUsize::new(x as *const _ as usize)
25                .expect("thread-local variable address is null")
26        })
27    }
28}
29
30/// A mutex which can be recursively locked by a single thread.
31///
32/// This type is identical to `Mutex` except for the following points:
33///
34/// - Locking multiple times from the same thread will work correctly instead of
35///   deadlocking.
36/// - `ReentrantMutexGuard` does not give mutable references to the locked data.
37///   Use a `RefCell` if you need this.
38///
39/// See [`Mutex`](crate::Mutex) for more details about the underlying mutex
40/// primitive.
41pub type ReentrantMutex<T> = lock_api::ReentrantMutex<RawMutex, RawThreadId, T>;
42
43/// Creates a new reentrant mutex in an unlocked state ready for use.
44///
45/// This allows creating a reentrant mutex in a constant context on stable Rust.
46pub const fn const_reentrant_mutex<T>(val: T) -> ReentrantMutex<T> {
47    ReentrantMutex::const_new(
48        <RawMutex as lock_api::RawMutex>::INIT,
49        <RawThreadId as lock_api::GetThreadId>::INIT,
50        val,
51    )
52}
53
54/// An RAII implementation of a "scoped lock" of a reentrant mutex. When this structure
55/// is dropped (falls out of scope), the lock will be unlocked.
56///
57/// The data protected by the mutex can be accessed through this guard via its
58/// `Deref` implementation.
59pub type ReentrantMutexGuard<'a, T> = lock_api::ReentrantMutexGuard<'a, RawMutex, RawThreadId, T>;
60
61/// An RAII mutex guard returned by `ReentrantMutexGuard::map`, which can point to a
62/// subfield of the protected data.
63///
64/// The main difference between `MappedReentrantMutexGuard` and `ReentrantMutexGuard` is that the
65/// former doesn't support temporarily unlocking and re-locking, since that
66/// could introduce soundness issues if the locked object is modified by another
67/// thread.
68pub type MappedReentrantMutexGuard<'a, T> =
69    lock_api::MappedReentrantMutexGuard<'a, RawMutex, RawThreadId, T>;
70
71#[cfg(test)]
72mod tests {
73    use crate::ReentrantMutex;
74    use crate::ReentrantMutexGuard;
75    use std::cell::RefCell;
76    use std::sync::mpsc::channel;
77    use std::sync::Arc;
78    use std::thread;
79
80    #[cfg(feature = "serde")]
81    use bincode::{deserialize, serialize};
82
83    #[test]
84    fn smoke() {
85        let m = ReentrantMutex::new(2);
86        {
87            let a = m.lock();
88            {
89                let b = m.lock();
90                {
91                    let c = m.lock();
92                    assert_eq!(*c, 2);
93                }
94                assert_eq!(*b, 2);
95            }
96            assert_eq!(*a, 2);
97        }
98    }
99
100    #[test]
101    fn is_mutex() {
102        let m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
103        let m2 = m.clone();
104        let lock = m.lock();
105        let child = thread::spawn(move || {
106            let lock = m2.lock();
107            assert_eq!(*lock.borrow(), 4950);
108        });
109        for i in 0..100 {
110            let lock = m.lock();
111            *lock.borrow_mut() += i;
112        }
113        drop(lock);
114        child.join().unwrap();
115    }
116
117    #[test]
118    fn trylock_works() {
119        let m = Arc::new(ReentrantMutex::new(()));
120        let m2 = m.clone();
121        let _lock = m.try_lock();
122        let _lock2 = m.try_lock();
123        thread::spawn(move || {
124            let lock = m2.try_lock();
125            assert!(lock.is_none());
126        })
127        .join()
128        .unwrap();
129        let _lock3 = m.try_lock();
130    }
131
132    #[test]
133    fn test_reentrant_mutex_debug() {
134        let mutex = ReentrantMutex::new(vec![0u8, 10]);
135
136        assert_eq!(format!("{:?}", mutex), "ReentrantMutex { data: [0, 10] }");
137    }
138
139    #[test]
140    fn test_reentrant_mutex_bump() {
141        let mutex = Arc::new(ReentrantMutex::new(()));
142        let mutex2 = mutex.clone();
143
144        let mut guard = mutex.lock();
145
146        let (tx, rx) = channel();
147
148        thread::spawn(move || {
149            let _guard = mutex2.lock();
150            tx.send(()).unwrap();
151        });
152
153        // `bump()` repeatedly until the thread starts up and requests the lock
154        while rx.try_recv().is_err() {
155            ReentrantMutexGuard::bump(&mut guard);
156        }
157    }
158
159    #[cfg(feature = "serde")]
160    #[test]
161    fn test_serde() {
162        let contents: Vec<u8> = vec![0, 1, 2];
163        let mutex = ReentrantMutex::new(contents.clone());
164
165        let serialized = serialize(&mutex).unwrap();
166        let deserialized: ReentrantMutex<Vec<u8>> = deserialize(&serialized).unwrap();
167
168        assert_eq!(*(mutex.lock()), *(deserialized.lock()));
169        assert_eq!(contents, *(deserialized.lock()));
170    }
171}
parking_lot/remutex.rs

parking_lot/
remutex.rs
