Struct lock_api::MappedRwLockWriteGuard

#[must_use = "if unused the RwLock will immediately unlock"]
pub struct MappedRwLockWriteGuard<'a, R: RawRwLock, T: ?Sized> { /* fields omitted */ }

An RAII write lock guard returned by RwLockWriteGuard::map, which can point to a subfield of the protected data.

The main difference between MappedRwLockWriteGuard and RwLockWriteGuard 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: RawRwLock + 'a, T: ?Sized + 'a> MappedRwLockWriteGuard<'a, R, T>

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

Make a new MappedRwLockWriteGuard for a component of the locked data.

This operation cannot fail as the MappedRwLockWriteGuard passed in already locked the data.

This is an associated function that needs to be used as MappedRwLockWriteGuard::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<MappedRwLockWriteGuard<'a, R, U>, Self> where
    F: FnOnce(&mut T) -> Option<&mut U>, 

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

This operation cannot fail as the MappedRwLockWriteGuard passed in already locked the data.

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

impl<'a, R: RawRwLockDowngrade + 'a, T: ?Sized + 'a> MappedRwLockWriteGuard<'a, R, T>

pub fn downgrade(s: Self) -> MappedRwLockReadGuard<'a, R, T>

Atomically downgrades a write lock into a read lock without allowing any writers to take exclusive access of the lock in the meantime.

Note that if there are any writers currently waiting to take the lock then other readers may not be able to acquire the lock even if it was downgraded.

impl<'a, R: RawRwLockFair + 'a, T: ?Sized + 'a> MappedRwLockWriteGuard<'a, R, T>

pub fn unlock_fair(s: Self)

Unlocks the RwLock using a fair unlock protocol.

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

Trait Implementations

impl<'a, R: RawRwLock + 'a, T: Display + ?Sized + 'a> Display for MappedRwLockWriteGuard<'a, R, T>

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl<'a, R: RawRwLock + 'a, T: Debug + ?Sized + 'a> Debug for MappedRwLockWriteGuard<'a, R, T>

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Deref for MappedRwLockWriteGuard<'a, R, T>

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &T

Dereferences the value.

impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> DerefMut for MappedRwLockWriteGuard<'a, R, T>

fn deref_mut(&mut self) -> &mut T

Mutably dereferences the value.

impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Drop for MappedRwLockWriteGuard<'a, R, T>

fn drop(&mut self)

Executes the destructor for this type.

impl<'a, R: RawRwLock + 'a, T: ?Sized + 'a> Send for MappedRwLockWriteGuard<'a, R, T> where
    R::GuardMarker: Send, 

impl<'a, R: RawRwLock + 'a, T: ?Sized + Sync + 'a> Sync for MappedRwLockWriteGuard<'a, R, T>