Struct lock_api::MappedReentrantMutexGuard

#[must_use]
pub struct MappedReentrantMutexGuard<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> { /* fields omitted */ }

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.

Methods

impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> MappedReentrantMutexGuard<'a, R, G, T>

pub fn map<U: ?Sized, F>(
    s: Self,
    f: F
) -> MappedReentrantMutexGuard<'a, R, G, U> where
    F: FnOnce(&T) -> &U, 

Makes a new MappedReentrantMutexGuard for a component of the locked data.

This operation cannot fail as the MappedReentrantMutexGuard passed in already locked the mutex.

This is an associated function that needs to be used as MappedReentrantMutexGuard::map(...). A method would interfere with methods of the same name on the contents of the locked data.

pub fn try_map<U: ?Sized, F>(
    s: Self,
    f: F
) -> Result<MappedReentrantMutexGuard<'a, R, G, U>, Self> where
    F: FnOnce(&T) -> Option<&U>, 

Attempts to make a new MappedReentrantMutexGuard for a component of the locked data. The original guard is return if the closure returns None.

This operation cannot fail as the MappedReentrantMutexGuard passed in already locked the mutex.

This is an associated function that needs to be used as MappedReentrantMutexGuard::map(...). A method would interfere with methods of the same name on the contents of the locked data.

impl<'a, R: RawMutexFair + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> MappedReentrantMutexGuard<'a, R, G, T>

pub fn unlock_fair(s: Self)

Unlocks the mutex using a fair unlock protocol.

By default, mutexes are unfair and allow the current thread to re-lock the mutex before another has the chance to acquire the lock, even if that thread has been blocked on the mutex for a long time. This is the default because it allows much higher throughput as it avoids forcing a context switch on every mutex unlock. This can result in one thread acquiring a mutex many more times than other threads.

However in some cases it can be beneficial to ensure fairness by forcing the lock to pass on to a waiting thread if there is one. This is done by using this method instead of dropping the ReentrantMutexGuard normally.

Trait Implementations

impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> Deref for MappedReentrantMutexGuard<'a, R, G, T>

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &T

Dereferences the value.

impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> Drop for MappedReentrantMutexGuard<'a, R, G, T>

fn drop(&mut self)

Executes the destructor for this type.

impl<'a, R: RawMutex + Sync + 'a, G: GetThreadId + Sync + 'a, T: ?Sized + Sync + 'a> Sync for MappedReentrantMutexGuard<'a, R, G, T>

impl<'a, R: RawMutex + 'a, G: GetThreadId + 'a, T: ?Sized + 'a> StableDeref for MappedReentrantMutexGuard<'a, R, G, T>