Type Alias parking_lot::Mutex
source · pub type Mutex<T> = Mutex<RawMutex, T>;
Expand description
A mutual exclusion primitive useful for protecting shared data
This mutex will block threads waiting for the lock to become available. The
mutex can be statically initialized or created by the 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 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.
- 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();
Aliased Type§
struct Mutex<T> { /* private fields */ }
Implementations
source§impl<R, T> Mutex<R, T>where
R: RawMutex,
impl<R, T> Mutex<R, T>where
R: RawMutex,
sourcepub const fn new(val: T) -> Mutex<R, T>
pub const fn new(val: T) -> Mutex<R, T>
Creates a new mutex in an unlocked state ready for use.
sourcepub fn into_inner(self) -> T
pub fn into_inner(self) -> T
Consumes this mutex, returning the underlying data.
source§impl<R, T> Mutex<R, T>
impl<R, T> Mutex<R, T>
source§impl<R, T> Mutex<R, T>
impl<R, T> Mutex<R, T>
sourcepub unsafe fn make_guard_unchecked(&self) -> MutexGuard<'_, R, T>
pub unsafe fn make_guard_unchecked(&self) -> MutexGuard<'_, R, T>
Creates a new MutexGuard
without checking if the mutex is locked.
§Safety
This method must only be called if the thread logically holds the lock.
Calling this function when a guard has already been produced is undefined behaviour unless
the guard was forgotten with mem::forget
.
sourcepub fn lock(&self) -> MutexGuard<'_, R, T>
pub fn lock(&self) -> MutexGuard<'_, R, T>
Acquires a mutex, blocking the current thread until it is able to do so.
This function will block the local thread until it is available to acquire the mutex. Upon returning, the thread is the only thread with the mutex held. An RAII guard is returned to allow scoped unlock of the lock. When the guard goes out of scope, the mutex will be unlocked.
Attempts to lock a mutex in the thread which already holds the lock will result in a deadlock.
sourcepub fn try_lock(&self) -> Option<MutexGuard<'_, R, T>>
pub fn try_lock(&self) -> Option<MutexGuard<'_, R, T>>
Attempts to acquire this lock.
If the lock could not be acquired at this time, then None
is returned.
Otherwise, an RAII guard is returned. The lock will be unlocked when the
guard is dropped.
This function does not block.
sourcepub fn get_mut(&mut self) -> &mut T
pub fn get_mut(&mut self) -> &mut T
Returns a mutable reference to the underlying data.
Since this call borrows the Mutex
mutably, no actual locking needs to
take place—the mutable borrow statically guarantees no locks exist.
sourcepub unsafe fn force_unlock(&self)
pub unsafe fn force_unlock(&self)
Forcibly unlocks the mutex.
This is useful when combined with mem::forget
to hold a lock without
the need to maintain a MutexGuard
object alive, for example when
dealing with FFI.
§Safety
This method must only be called if the current thread logically owns a
MutexGuard
but that guard has been discarded using mem::forget
.
Behavior is undefined if a mutex is unlocked when not locked.
sourcepub unsafe fn raw(&self) -> &R
pub unsafe fn raw(&self) -> &R
Returns the underlying raw mutex object.
Note that you will most likely need to import the RawMutex
trait from
lock_api
to be able to call functions on the raw mutex.
§Safety
This method is unsafe because it allows unlocking a mutex while
still holding a reference to a MutexGuard
.
sourcepub fn data_ptr(&self) -> *mut T
pub fn data_ptr(&self) -> *mut T
Returns a raw pointer to the underlying data.
This is useful when combined with mem::forget
to hold a lock without
the need to maintain a MutexGuard
object alive, for example when
dealing with FFI.
§Safety
You must ensure that there are no data races when dereferencing the
returned pointer, for example if the current thread logically owns
a MutexGuard
but that guard has been discarded using mem::forget
.
source§impl<R, T> Mutex<R, T>where
R: RawMutexFair,
T: ?Sized,
impl<R, T> Mutex<R, T>where
R: RawMutexFair,
T: ?Sized,
sourcepub unsafe fn force_unlock_fair(&self)
pub unsafe fn force_unlock_fair(&self)
Forcibly unlocks the mutex using a fair unlock protocol.
This is useful when combined with mem::forget
to hold a lock without
the need to maintain a MutexGuard
object alive, for example when
dealing with FFI.
§Safety
This method must only be called if the current thread logically owns a
MutexGuard
but that guard has been discarded using mem::forget
.
Behavior is undefined if a mutex is unlocked when not locked.
source§impl<R, T> Mutex<R, T>where
R: RawMutexTimed,
T: ?Sized,
impl<R, T> Mutex<R, T>where
R: RawMutexTimed,
T: ?Sized,
sourcepub fn try_lock_for(
&self,
timeout: <R as RawMutexTimed>::Duration,
) -> Option<MutexGuard<'_, R, T>>
pub fn try_lock_for( &self, timeout: <R as RawMutexTimed>::Duration, ) -> Option<MutexGuard<'_, R, T>>
Attempts to acquire this lock until a timeout is reached.
If the lock could not be acquired before the timeout expired, then
None
is returned. Otherwise, an RAII guard is returned. The lock will
be unlocked when the guard is dropped.
sourcepub fn try_lock_until(
&self,
timeout: <R as RawMutexTimed>::Instant,
) -> Option<MutexGuard<'_, R, T>>
pub fn try_lock_until( &self, timeout: <R as RawMutexTimed>::Instant, ) -> Option<MutexGuard<'_, R, T>>
Attempts to acquire this lock until a timeout is reached.
If the lock could not be acquired before the timeout expired, then
None
is returned. Otherwise, an RAII guard is returned. The lock will
be unlocked when the guard is dropped.