Struct lock_api::RwLock

pub struct RwLock<R, T: ?Sized> { /* private fields */ }

A reader-writer lock

This type of lock allows a number of readers or at most one writer at any point in time. The write portion of this lock typically allows modification of the underlying data (exclusive access) and the read portion of this lock typically allows for read-only access (shared access).

The type parameter T represents the data that this lock protects. It is required that T satisfies Send to be shared across threads and Sync to allow concurrent access through readers. The RAII guards returned from the locking methods implement Deref (and DerefMut for the write methods) to allow access to the contained of the lock.

Implementations

impl<R: RawRwLock, T> RwLock<R, T>

pub const fn new(val: T) -> RwLock<R, T>

Available on has_const_fn_trait_bound only.

Creates a new instance of an RwLock<T> which is unlocked.

pub fn into_inner(self) -> T

Consumes this RwLock, returning the underlying data.

impl<R, T> RwLock<R, T>

pub const fn from_raw(raw_rwlock: R, val: T) -> RwLock<R, T>

Creates a new new instance of an RwLock<T> based on a pre-existing RawRwLock<T>.

pub const fn const_new(raw_rwlock: R, val: T) -> RwLock<R, T>

Creates a new new instance of an RwLock<T> based on a pre-existing RawRwLock<T>.

This allows creating a RwLock<T> in a constant context on stable Rust.

This method is a legacy alias for from_raw.

impl<R: RawRwLock, T: ?Sized> RwLock<R, T>

pub unsafe fn make_read_guard_unchecked(&self) -> RwLockReadGuard<'_, R, T>

Creates a new RwLockReadGuard without checking if the lock is held.

Safety

This method must only be called if the thread logically holds a read lock.

This function does not increment the read count of the lock. Calling this function when a guard has already been produced is undefined behaviour unless the guard was forgotten with mem::forget.

pub unsafe fn make_write_guard_unchecked(&self) -> RwLockWriteGuard<'_, R, T>

Creates a new RwLockReadGuard without checking if the lock is held.

Safety

This method must only be called if the thread logically holds a write lock.

Calling this function when a guard has already been produced is undefined behaviour unless the guard was forgotten with mem::forget.

pub fn read(&self) -> RwLockReadGuard<'_, R, T>

Locks this RwLock with shared read access, blocking the current thread until it can be acquired.

The calling thread will be blocked until there are no more writers which hold the lock. There may be other readers currently inside the lock when this method returns.

Note that attempts to recursively acquire a read lock on a RwLock when the current thread already holds one may result in a deadlock.

Returns an RAII guard which will release this thread’s shared access once it is dropped.

pub fn try_read(&self) -> Option<RwLockReadGuard<'_, R, T>>

Attempts to acquire this RwLock with shared read access.

If the access could not be granted at this time, then None is returned. Otherwise, an RAII guard is returned which will release the shared access when it is dropped.

This function does not block.

pub fn write(&self) -> RwLockWriteGuard<'_, R, T>

Locks this RwLock with exclusive write access, blocking the current thread until it can be acquired.

This function will not return while other writers or other readers currently have access to the lock.

Returns an RAII guard which will drop the write access of this RwLock when dropped.

pub fn try_write(&self) -> Option<RwLockWriteGuard<'_, R, T>>

Attempts to lock this RwLock with exclusive write access.

If the lock could not be acquired at this time, then None is returned. Otherwise, an RAII guard is returned which will release the lock when it is dropped.

This function does not block.

pub fn get_mut(&mut self) -> &mut T

Returns a mutable reference to the underlying data.

Since this call borrows the RwLock mutably, no actual locking needs to take place—the mutable borrow statically guarantees no locks exist.

pub fn is_locked(&self) -> bool

Checks whether this RwLock is currently locked in any way.

pub fn is_locked_exclusive(&self) -> bool

Check if this RwLock is currently exclusively locked.

pub unsafe fn force_unlock_read(&self)

Forcibly unlocks a read lock.

This is useful when combined with mem::forget to hold a lock without the need to maintain a RwLockReadGuard object alive, for example when dealing with FFI.

Safety

This method must only be called if the current thread logically owns a RwLockReadGuard but that guard has be discarded using mem::forget. Behavior is undefined if a rwlock is read-unlocked when not read-locked.

pub unsafe fn force_unlock_write(&self)

Forcibly unlocks a write lock.

This is useful when combined with mem::forget to hold a lock without the need to maintain a RwLockWriteGuard object alive, for example when dealing with FFI.

Safety

This method must only be called if the current thread logically owns a RwLockWriteGuard but that guard has be discarded using mem::forget. Behavior is undefined if a rwlock is write-unlocked when not write-locked.

pub unsafe fn raw(&self) -> &R

Returns the underlying raw reader-writer lock object.

Note that you will most likely need to import the RawRwLock trait from lock_api to be able to call functions on the raw reader-writer lock.

Safety

This method is unsafe because it allows unlocking a mutex while still holding a reference to a lock guard.

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 RwLockReadGuard or RwLockWriteGuard 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 RwLockReadGuard or RwLockWriteGuard but that guard has been discarded using mem::forget.

impl<R: RawRwLockFair, T: ?Sized> RwLock<R, T>

pub unsafe fn force_unlock_read_fair(&self)

Forcibly unlocks a read lock using a fair unlock protocol.

This is useful when combined with mem::forget to hold a lock without the need to maintain a RwLockReadGuard object alive, for example when dealing with FFI.

Safety

This method must only be called if the current thread logically owns a RwLockReadGuard but that guard has be discarded using mem::forget. Behavior is undefined if a rwlock is read-unlocked when not read-locked.

pub unsafe fn force_unlock_write_fair(&self)

Forcibly unlocks a write lock using a fair unlock protocol.

This is useful when combined with mem::forget to hold a lock without the need to maintain a RwLockWriteGuard object alive, for example when dealing with FFI.

Safety

This method must only be called if the current thread logically owns a RwLockWriteGuard but that guard has be discarded using mem::forget. Behavior is undefined if a rwlock is write-unlocked when not write-locked.

impl<R: RawRwLockTimed, T: ?Sized> RwLock<R, T>

pub fn try_read_for( &self, timeout: R::Duration, ) -> Option<RwLockReadGuard<'_, R, T>>

Attempts to acquire this RwLock with shared read access until a timeout is reached.

If the access could not be granted before the timeout expires, then None is returned. Otherwise, an RAII guard is returned which will release the shared access when it is dropped.

pub fn try_read_until( &self, timeout: R::Instant, ) -> Option<RwLockReadGuard<'_, R, T>>

Attempts to acquire this RwLock with shared read access until a timeout is reached.

If the access could not be granted before the timeout expires, then None is returned. Otherwise, an RAII guard is returned which will release the shared access when it is dropped.

pub fn try_write_for( &self, timeout: R::Duration, ) -> Option<RwLockWriteGuard<'_, R, T>>

Attempts to acquire this RwLock with exclusive write access until a timeout is reached.

If the access could not be granted before the timeout expires, then None is returned. Otherwise, an RAII guard is returned which will release the exclusive access when it is dropped.

pub fn try_write_until( &self, timeout: R::Instant, ) -> Option<RwLockWriteGuard<'_, R, T>>

Attempts to acquire this RwLock with exclusive write access until a timeout is reached.

If the access could not be granted before the timeout expires, then None is returned. Otherwise, an RAII guard is returned which will release the exclusive access when it is dropped.

impl<R: RawRwLockRecursive, T: ?Sized> RwLock<R, T>

pub fn read_recursive(&self) -> RwLockReadGuard<'_, R, T>

Locks this RwLock with shared read access, blocking the current thread until it can be acquired.

The calling thread will be blocked until there are no more writers which hold the lock. There may be other readers currently inside the lock when this method returns.

Unlike read, this method is guaranteed to succeed without blocking if another read lock is held at the time of the call. This allows a thread to recursively lock a RwLock. However using this method can cause writers to starve since readers no longer block if a writer is waiting for the lock.

Returns an RAII guard which will release this thread’s shared access once it is dropped.

pub fn try_read_recursive(&self) -> Option<RwLockReadGuard<'_, R, T>>

Attempts to acquire this RwLock with shared read access.

If the access could not be granted at this time, then None is returned. Otherwise, an RAII guard is returned which will release the shared access when it is dropped.

This method is guaranteed to succeed if another read lock is held at the time of the call. See the documentation for read_recursive for details.

This function does not block.

impl<R: RawRwLockRecursiveTimed, T: ?Sized> RwLock<R, T>

pub fn try_read_recursive_for( &self, timeout: R::Duration, ) -> Option<RwLockReadGuard<'_, R, T>>

Attempts to acquire this RwLock with shared read access until a timeout is reached.

If the access could not be granted before the timeout expires, then None is returned. Otherwise, an RAII guard is returned which will release the shared access when it is dropped.

This method is guaranteed to succeed without blocking if another read lock is held at the time of the call. See the documentation for read_recursive for details.

pub fn try_read_recursive_until( &self, timeout: R::Instant, ) -> Option<RwLockReadGuard<'_, R, T>>

Attempts to acquire this RwLock with shared read access until a timeout is reached.

If the access could not be granted before the timeout expires, then None is returned. Otherwise, an RAII guard is returned which will release the shared access when it is dropped.

impl<R: RawRwLockUpgrade, T: ?Sized> RwLock<R, T>

pub unsafe fn make_upgradable_guard_unchecked( &self, ) -> RwLockUpgradableReadGuard<'_, R, T>

Creates a new RwLockUpgradableReadGuard without checking if the lock is held.

Safety

This method must only be called if the thread logically holds an upgradable read lock.

This function does not increment the read count of the lock. Calling this function when a guard has already been produced is undefined behaviour unless the guard was forgotten with mem::forget.

pub fn upgradable_read(&self) -> RwLockUpgradableReadGuard<'_, R, T>

Locks this RwLock with upgradable read access, blocking the current thread until it can be acquired.

The calling thread will be blocked until there are no more writers or other upgradable reads which hold the lock. There may be other readers currently inside the lock when this method returns.

Returns an RAII guard which will release this thread’s shared access once it is dropped.

pub fn try_upgradable_read(&self) -> Option<RwLockUpgradableReadGuard<'_, R, T>>

Attempts to acquire this RwLock with upgradable read access.

If the access could not be granted at this time, then None is returned. Otherwise, an RAII guard is returned which will release the shared access when it is dropped.

This function does not block.

impl<R: RawRwLockUpgradeTimed, T: ?Sized> RwLock<R, T>

pub fn try_upgradable_read_for( &self, timeout: R::Duration, ) -> Option<RwLockUpgradableReadGuard<'_, R, T>>

Attempts to acquire this RwLock with upgradable read access until a timeout is reached.

If the access could not be granted before the timeout expires, then None is returned. Otherwise, an RAII guard is returned which will release the shared access when it is dropped.

pub fn try_upgradable_read_until( &self, timeout: R::Instant, ) -> Option<RwLockUpgradableReadGuard<'_, R, T>>

Attempts to acquire this RwLock with upgradable read access until a timeout is reached.

If the access could not be granted before the timeout expires, then None is returned. Otherwise, an RAII guard is returned which will release the shared access when it is dropped.

Trait Implementations

impl<R: RawRwLock, T: ?Sized + Debug> Debug for RwLock<R, T>

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

Formats the value using the given formatter.

impl<R: RawRwLock, T: ?Sized + Default> Default for RwLock<R, T>

fn default() -> RwLock<R, T>

Returns the “default value” for a type.

impl<R: RawRwLock, T> From<T> for RwLock<R, T>

fn from(t: T) -> RwLock<R, T>

Converts to this type from the input type.

impl<R: RawRwLock + Send, T: ?Sized + Send> Send for RwLock<R, T>

impl<R: RawRwLock + Sync, T: ?Sized + Send + Sync> Sync for RwLock<R, T>