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// Copyright 2016 Amanieu d'Antras
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
// http://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.
use crate::raw_mutex::RawMutex;
use core::num::NonZeroUsize;
use lock_api::{self, GetThreadId};
/// Implementation of the `GetThreadId` trait for `lock_api::ReentrantMutex`.
pub struct RawThreadId;
unsafe impl GetThreadId for RawThreadId {
const INIT: RawThreadId = RawThreadId;
fn nonzero_thread_id(&self) -> NonZeroUsize {
// The address of a thread-local variable is guaranteed to be unique to the
// current thread, and is also guaranteed to be non-zero. The variable has to have a
// non-zero size to guarantee it has a unique address for each thread.
thread_local!(static KEY: u8 = 0);
KEY.with(|x| {
NonZeroUsize::new(x as *const _ as usize)
.expect("thread-local variable address is null")
})
}
}
/// A mutex which can be recursively locked by a single thread.
///
/// This type is identical to `Mutex` except for the following points:
///
/// - Locking multiple times from the same thread will work correctly instead of
/// deadlocking.
/// - `ReentrantMutexGuard` does not give mutable references to the locked data.
/// Use a `RefCell` if you need this.
///
/// See [`Mutex`](type.Mutex.html) for more details about the underlying mutex
/// primitive.
pub type ReentrantMutex<T> = lock_api::ReentrantMutex<RawMutex, RawThreadId, T>;
/// Creates a new reentrant mutex in an unlocked state ready for use.
///
/// This allows creating a reentrant mutex in a constant context on stable Rust.
pub const fn const_reentrant_mutex<T>(val: T) -> ReentrantMutex<T> {
ReentrantMutex::const_new(
<RawMutex as lock_api::RawMutex>::INIT,
<RawThreadId as lock_api::GetThreadId>::INIT,
val,
)
}
/// An RAII implementation of a "scoped lock" of a reentrant mutex. When this structure
/// is dropped (falls out of scope), the lock will be unlocked.
///
/// The data protected by the mutex can be accessed through this guard via its
/// `Deref` implementation.
pub type ReentrantMutexGuard<'a, T> = lock_api::ReentrantMutexGuard<'a, RawMutex, RawThreadId, T>;
/// An RAII mutex guard returned by `ReentrantMutexGuard::map`, which can point to a
/// subfield of the protected data.
///
/// The main difference between `MappedReentrantMutexGuard` and `ReentrantMutexGuard` is that the
/// former doesn't support temporarily unlocking and re-locking, since that
/// could introduce soundness issues if the locked object is modified by another
/// thread.
pub type MappedReentrantMutexGuard<'a, T> =
lock_api::MappedReentrantMutexGuard<'a, RawMutex, RawThreadId, T>;
#[cfg(test)]
mod tests {
use crate::ReentrantMutex;
use std::cell::RefCell;
use std::sync::Arc;
use std::thread;
#[cfg(feature = "serde")]
use bincode::{deserialize, serialize};
#[test]
fn smoke() {
let m = ReentrantMutex::new(2);
{
let a = m.lock();
{
let b = m.lock();
{
let c = m.lock();
assert_eq!(*c, 2);
}
assert_eq!(*b, 2);
}
assert_eq!(*a, 2);
}
}
#[test]
fn is_mutex() {
let m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
let m2 = m.clone();
let lock = m.lock();
let child = thread::spawn(move || {
let lock = m2.lock();
assert_eq!(*lock.borrow(), 4950);
});
for i in 0..100 {
let lock = m.lock();
*lock.borrow_mut() += i;
}
drop(lock);
child.join().unwrap();
}
#[test]
fn trylock_works() {
let m = Arc::new(ReentrantMutex::new(()));
let m2 = m.clone();
let _lock = m.try_lock();
let _lock2 = m.try_lock();
thread::spawn(move || {
let lock = m2.try_lock();
assert!(lock.is_none());
})
.join()
.unwrap();
let _lock3 = m.try_lock();
}
#[test]
fn test_reentrant_mutex_debug() {
let mutex = ReentrantMutex::new(vec![0u8, 10]);
assert_eq!(format!("{:?}", mutex), "ReentrantMutex { data: [0, 10] }");
}
#[cfg(feature = "serde")]
#[test]
fn test_serde() {
let contents: Vec<u8> = vec![0, 1, 2];
let mutex = ReentrantMutex::new(contents.clone());
let serialized = serialize(&mutex).unwrap();
let deserialized: ReentrantMutex<Vec<u8>> = deserialize(&serialized).unwrap();
assert_eq!(*(mutex.lock()), *(deserialized.lock()));
assert_eq!(contents, *(deserialized.lock()));
}
}