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Diffstat (limited to 'third_party/rust/parking_lot/src/mutex.rs')
| -rw-r--r-- | third_party/rust/parking_lot/src/mutex.rs | 312 |
1 files changed, 312 insertions, 0 deletions
diff --git a/third_party/rust/parking_lot/src/mutex.rs b/third_party/rust/parking_lot/src/mutex.rs new file mode 100644 index 0000000000..9f63cb9434 --- /dev/null +++ b/third_party/rust/parking_lot/src/mutex.rs @@ -0,0 +1,312 @@ +// 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 lock_api; + +/// A mutual exclusion primitive useful for protecting shared data +/// +/// This mutex will block threads waiting for the lock to become available. The +/// mutex can also be statically initialized or created via a `new` +/// constructor. Each mutex has a type parameter which represents the data that +/// it is protecting. The data can only be accessed through the RAII guards +/// returned from `lock` and `try_lock`, which guarantees that the data is only +/// ever accessed when the mutex is locked. +/// +/// # Fairness +/// +/// A typical unfair lock can often end up in a situation where a single thread +/// quickly acquires and releases the same mutex in succession, which can starve +/// other threads waiting to acquire the mutex. While this improves throughput +/// because it doesn't force a context switch when a thread tries to re-acquire +/// a mutex it has just released, this can starve other threads. +/// +/// This mutex uses [eventual fairness](https://trac.webkit.org/changeset/203350) +/// to ensure that the lock will be fair on average without sacrificing +/// throughput. This is done by forcing a fair unlock on average every 0.5ms, +/// which will force the lock to go to the next thread waiting for the mutex. +/// +/// Additionally, any critical section longer than 1ms will always use a fair +/// unlock, which has a negligible impact on throughput considering the length +/// of the critical section. +/// +/// You can also force a fair unlock by calling `MutexGuard::unlock_fair` when +/// unlocking a mutex instead of simply dropping the `MutexGuard`. +/// +/// # Differences from the standard library `Mutex` +/// +/// - No poisoning, the lock is released normally on panic. +/// - Only requires 1 byte of space, whereas the standard library boxes the +/// `Mutex` due to platform limitations. +/// - Can be statically constructed (requires the `const_fn` nightly feature). +/// - Does not require any drop glue when dropped. +/// - Inline fast path for the uncontended case. +/// - Efficient handling of micro-contention using adaptive spinning. +/// - Allows raw locking & unlocking without a guard. +/// - Supports eventual fairness so that the mutex is fair on average. +/// - Optionally allows making the mutex fair by calling `MutexGuard::unlock_fair`. +/// +/// # Examples +/// +/// ``` +/// use parking_lot::Mutex; +/// use std::sync::{Arc, mpsc::channel}; +/// use std::thread; +/// +/// const N: usize = 10; +/// +/// // Spawn a few threads to increment a shared variable (non-atomically), and +/// // let the main thread know once all increments are done. +/// // +/// // Here we're using an Arc to share memory among threads, and the data inside +/// // the Arc is protected with a mutex. +/// let data = Arc::new(Mutex::new(0)); +/// +/// let (tx, rx) = channel(); +/// for _ in 0..10 { +/// let (data, tx) = (Arc::clone(&data), tx.clone()); +/// thread::spawn(move || { +/// // The shared state can only be accessed once the lock is held. +/// // Our non-atomic increment is safe because we're the only thread +/// // which can access the shared state when the lock is held. +/// let mut data = data.lock(); +/// *data += 1; +/// if *data == N { +/// tx.send(()).unwrap(); +/// } +/// // the lock is unlocked here when `data` goes out of scope. +/// }); +/// } +/// +/// rx.recv().unwrap(); +/// ``` +pub type Mutex<T> = lock_api::Mutex<RawMutex, T>; + +/// Creates a new mutex in an unlocked state ready for use. +/// +/// This allows creating a mutex in a constant context on stable Rust. +pub const fn const_mutex<T>(val: T) -> Mutex<T> { + Mutex::const_new(<RawMutex as lock_api::RawMutex>::INIT, val) +} + +/// An RAII implementation of a "scoped lock" of a 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` and `DerefMut` implementations. +pub type MutexGuard<'a, T> = lock_api::MutexGuard<'a, RawMutex, T>; + +/// An RAII mutex guard returned by `MutexGuard::map`, which can point to a +/// subfield of the protected data. +/// +/// The main difference between `MappedMutexGuard` and `MutexGuard` 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 MappedMutexGuard<'a, T> = lock_api::MappedMutexGuard<'a, RawMutex, T>; + +#[cfg(test)] +mod tests { + use crate::{Condvar, Mutex}; + use std::sync::atomic::{AtomicUsize, Ordering}; + use std::sync::mpsc::channel; + use std::sync::Arc; + use std::thread; + + #[cfg(feature = "serde")] + use bincode::{deserialize, serialize}; + + struct Packet<T>(Arc<(Mutex<T>, Condvar)>); + + #[derive(Eq, PartialEq, Debug)] + struct NonCopy(i32); + + unsafe impl<T: Send> Send for Packet<T> {} + unsafe impl<T> Sync for Packet<T> {} + + #[test] + fn smoke() { + let m = Mutex::new(()); + drop(m.lock()); + drop(m.lock()); + } + + #[test] + fn lots_and_lots() { + const J: u32 = 1000; + const K: u32 = 3; + + let m = Arc::new(Mutex::new(0)); + + fn inc(m: &Mutex<u32>) { + for _ in 0..J { + *m.lock() += 1; + } + } + + let (tx, rx) = channel(); + for _ in 0..K { + let tx2 = tx.clone(); + let m2 = m.clone(); + thread::spawn(move || { + inc(&m2); + tx2.send(()).unwrap(); + }); + let tx2 = tx.clone(); + let m2 = m.clone(); + thread::spawn(move || { + inc(&m2); + tx2.send(()).unwrap(); + }); + } + + drop(tx); + for _ in 0..2 * K { + rx.recv().unwrap(); + } + assert_eq!(*m.lock(), J * K * 2); + } + + #[test] + fn try_lock() { + let m = Mutex::new(()); + *m.try_lock().unwrap() = (); + } + + #[test] + fn test_into_inner() { + let m = Mutex::new(NonCopy(10)); + assert_eq!(m.into_inner(), NonCopy(10)); + } + + #[test] + fn test_into_inner_drop() { + struct Foo(Arc<AtomicUsize>); + impl Drop for Foo { + fn drop(&mut self) { + self.0.fetch_add(1, Ordering::SeqCst); + } + } + let num_drops = Arc::new(AtomicUsize::new(0)); + let m = Mutex::new(Foo(num_drops.clone())); + assert_eq!(num_drops.load(Ordering::SeqCst), 0); + { + let _inner = m.into_inner(); + assert_eq!(num_drops.load(Ordering::SeqCst), 0); + } + assert_eq!(num_drops.load(Ordering::SeqCst), 1); + } + + #[test] + fn test_get_mut() { + let mut m = Mutex::new(NonCopy(10)); + *m.get_mut() = NonCopy(20); + assert_eq!(m.into_inner(), NonCopy(20)); + } + + #[test] + fn test_mutex_arc_condvar() { + let packet = Packet(Arc::new((Mutex::new(false), Condvar::new()))); + let packet2 = Packet(packet.0.clone()); + let (tx, rx) = channel(); + let _t = thread::spawn(move || { + // wait until parent gets in + rx.recv().unwrap(); + let &(ref lock, ref cvar) = &*packet2.0; + let mut lock = lock.lock(); + *lock = true; + cvar.notify_one(); + }); + + let &(ref lock, ref cvar) = &*packet.0; + let mut lock = lock.lock(); + tx.send(()).unwrap(); + assert!(!*lock); + while !*lock { + cvar.wait(&mut lock); + } + } + + #[test] + fn test_mutex_arc_nested() { + // Tests nested mutexes and access + // to underlying data. + let arc = Arc::new(Mutex::new(1)); + let arc2 = Arc::new(Mutex::new(arc)); + let (tx, rx) = channel(); + let _t = thread::spawn(move || { + let lock = arc2.lock(); + let lock2 = lock.lock(); + assert_eq!(*lock2, 1); + tx.send(()).unwrap(); + }); + rx.recv().unwrap(); + } + + #[test] + fn test_mutex_arc_access_in_unwind() { + let arc = Arc::new(Mutex::new(1)); + let arc2 = arc.clone(); + let _ = thread::spawn(move || { + struct Unwinder { + i: Arc<Mutex<i32>>, + } + impl Drop for Unwinder { + fn drop(&mut self) { + *self.i.lock() += 1; + } + } + let _u = Unwinder { i: arc2 }; + panic!(); + }) + .join(); + let lock = arc.lock(); + assert_eq!(*lock, 2); + } + + #[test] + fn test_mutex_unsized() { + let mutex: &Mutex<[i32]> = &Mutex::new([1, 2, 3]); + { + let b = &mut *mutex.lock(); + b[0] = 4; + b[2] = 5; + } + let comp: &[i32] = &[4, 2, 5]; + assert_eq!(&*mutex.lock(), comp); + } + + #[test] + fn test_mutexguard_sync() { + fn sync<T: Sync>(_: T) {} + + let mutex = Mutex::new(()); + sync(mutex.lock()); + } + + #[test] + fn test_mutex_debug() { + let mutex = Mutex::new(vec![0u8, 10]); + + assert_eq!(format!("{:?}", mutex), "Mutex { data: [0, 10] }"); + let _lock = mutex.lock(); + assert_eq!(format!("{:?}", mutex), "Mutex { data: <locked> }"); + } + + #[cfg(feature = "serde")] + #[test] + fn test_serde() { + let contents: Vec<u8> = vec![0, 1, 2]; + let mutex = Mutex::new(contents.clone()); + + let serialized = serialize(&mutex).unwrap(); + let deserialized: Mutex<Vec<u8>> = deserialize(&serialized).unwrap(); + + assert_eq!(*(mutex.lock()), *(deserialized.lock())); + assert_eq!(contents, *(deserialized.lock())); + } +} |