Type Alias holochain::prelude::kitsune_p2p::dependencies::kitsune_p2p_types::dependencies::lair_keystore_api::dependencies::parking_lot::RwLock
source · pub type RwLock<T> = RwLock<RawRwLock, T>;Expand description
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).
This lock uses a task-fair locking policy which avoids both reader and writer starvation. This means that readers trying to acquire the lock will block even if the lock is unlocked when there are writers waiting to acquire the lock. Because of this, attempts to recursively acquire a read lock within a single thread may result in a deadlock.
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.
Fairness
A typical unfair lock can often end up in a situation where a single thread quickly acquires and releases the same lock in succession, which can starve other threads waiting to acquire the rwlock. While this improves throughput because it doesn’t force a context switch when a thread tries to re-acquire a rwlock it has just released, this can starve other threads.
This rwlock 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 rwlock.
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 RwLockReadGuard::unlock_fair
or RwLockWriteGuard::unlock_fair when unlocking a mutex instead of simply
dropping the guard.
Differences from the standard library RwLock
- Supports atomically downgrading a write lock into a read lock.
- Task-fair locking policy instead of an unspecified platform default.
- No poisoning, the lock is released normally on panic.
- Only requires 1 word of space, whereas the standard library boxes the
RwLockdue 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 rwlock is fair on average.
- Optionally allows making the rwlock fair by calling
RwLockReadGuard::unlock_fairandRwLockWriteGuard::unlock_fair.
Examples
use parking_lot::RwLock;
let lock = RwLock::new(5);
// many reader locks can be held at once
{
let r1 = lock.read();
let r2 = lock.read();
assert_eq!(*r1, 5);
assert_eq!(*r2, 5);
} // read locks are dropped at this point
// only one write lock may be held, however
{
let mut w = lock.write();
*w += 1;
assert_eq!(*w, 6);
} // write lock is dropped hereAliased Type§
struct RwLock<T> { /* private fields */ }Implementations§
§impl<R, T> RwLock<R, T>where
R: RawRwLock,
impl<R, T> RwLock<R, T>where R: RawRwLock,
pub fn into_inner(self) -> T
pub fn into_inner(self) -> T
Consumes this RwLock, returning the underlying data.
§impl<R, T> RwLock<R, T>where
R: RawRwLock,
T: ?Sized,
impl<R, T> RwLock<R, T>where R: RawRwLock, T: ?Sized,
pub fn read(&self) -> RwLockReadGuard<'_, R, T>
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>>
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>
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>>
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
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_exclusive(&self) -> bool
pub fn is_locked_exclusive(&self) -> bool
Check if this RwLock is currently exclusively locked.
pub unsafe fn force_unlock_read(&self)
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)
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
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
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, T> RwLock<R, T>where
R: RawRwLockFair,
T: ?Sized,
impl<R, T> RwLock<R, T>where R: RawRwLockFair, T: ?Sized,
pub unsafe fn force_unlock_read_fair(&self)
pub unsafe fn force_unlock_read_fair(&self)
Forcibly unlocks a read lock using a fair unlock procotol.
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)
pub unsafe fn force_unlock_write_fair(&self)
Forcibly unlocks a write lock using a fair unlock procotol.
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, T> RwLock<R, T>where
R: RawRwLockTimed,
T: ?Sized,
impl<R, T> RwLock<R, T>where R: RawRwLockTimed, T: ?Sized,
pub fn try_read_for(
&self,
timeout: <R as RawRwLockTimed>::Duration
) -> Option<RwLockReadGuard<'_, R, T>>
pub fn try_read_for( &self, timeout: <R as RawRwLockTimed>::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 as RawRwLockTimed>::Instant
) -> Option<RwLockReadGuard<'_, R, T>>
pub fn try_read_until( &self, timeout: <R as RawRwLockTimed>::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 as RawRwLockTimed>::Duration
) -> Option<RwLockWriteGuard<'_, R, T>>
pub fn try_write_for( &self, timeout: <R as RawRwLockTimed>::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 as RawRwLockTimed>::Instant
) -> Option<RwLockWriteGuard<'_, R, T>>
pub fn try_write_until( &self, timeout: <R as RawRwLockTimed>::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, T> RwLock<R, T>where
R: RawRwLockRecursive,
T: ?Sized,
impl<R, T> RwLock<R, T>where R: RawRwLockRecursive, T: ?Sized,
pub fn read_recursive(&self) -> RwLockReadGuard<'_, 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>>
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, T> RwLock<R, T>where
R: RawRwLockRecursiveTimed,
T: ?Sized,
impl<R, T> RwLock<R, T>where R: RawRwLockRecursiveTimed, T: ?Sized,
pub fn try_read_recursive_for(
&self,
timeout: <R as RawRwLockTimed>::Duration
) -> Option<RwLockReadGuard<'_, R, T>>
pub fn try_read_recursive_for( &self, timeout: <R as RawRwLockTimed>::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 as RawRwLockTimed>::Instant
) -> Option<RwLockReadGuard<'_, R, T>>
pub fn try_read_recursive_until( &self, timeout: <R as RawRwLockTimed>::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, T> RwLock<R, T>where
R: RawRwLockUpgrade,
T: ?Sized,
impl<R, T> RwLock<R, T>where R: RawRwLockUpgrade, T: ?Sized,
pub fn upgradable_read(&self) -> RwLockUpgradableReadGuard<'_, R, T>
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>>
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, T> RwLock<R, T>where
R: RawRwLockUpgradeTimed,
T: ?Sized,
impl<R, T> RwLock<R, T>where R: RawRwLockUpgradeTimed, T: ?Sized,
pub fn try_upgradable_read_for(
&self,
timeout: <R as RawRwLockTimed>::Duration
) -> Option<RwLockUpgradableReadGuard<'_, R, T>>
pub fn try_upgradable_read_for( &self, timeout: <R as RawRwLockTimed>::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 as RawRwLockTimed>::Instant
) -> Option<RwLockUpgradableReadGuard<'_, R, T>>
pub fn try_upgradable_read_until( &self, timeout: <R as RawRwLockTimed>::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.