ReentrantReadWriteLock.WriteLock

public static class ReentrantReadWriteLock.WriteLock extends Object
implements Lock Serializable

The lock returned by method ReentrantReadWriteLock.writeLock().

Protected Constructor Summary

WriteLock(ReentrantReadWriteLock lock) Constructor for use by subclasses.

Public Method Summary

int	getHoldCount() Queries the number of holds on this write lock by the current thread.
boolean	isHeldByCurrentThread() Queries if this write lock is held by the current thread.
void	lock() Acquires the write lock.
void	lockInterruptibly() Acquires the write lock unless the current thread is {@linkplain Thread#interrupt interrupted}.
Condition	newCondition() Returns a Condition instance for use with this Lock instance.
String	toString() Returns a string identifying this lock, as well as its lock state.
boolean	tryLock() Acquires the write lock only if it is not held by another thread at the time of invocation.
boolean	tryLock(long timeout, TimeUnit unit) Acquires the write lock if it is not held by another thread within the given waiting time and the current thread has not been {@linkplain Thread#interrupt interrupted}.
void	unlock() Attempts to release this lock.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

From interface java.util.concurrent.locks.Lock

abstract void	lock() Acquires the lock.
abstract void	lockInterruptibly() Acquires the lock unless the current thread is {@linkplain Thread#interrupt interrupted}.
abstract Condition	newCondition() Returns a new Condition instance that is bound to this Lock instance.
abstract boolean	tryLock() Acquires the lock only if it is free at the time of invocation.
abstract boolean	tryLock(long time, TimeUnit unit) Acquires the lock if it is free within the given waiting time and the current thread has not been {@linkplain Thread#interrupt interrupted}.
abstract void	unlock() Releases the lock.

Protected Constructors

protected WriteLock (ReentrantReadWriteLock lock)

Constructor for use by subclasses.

Parameters

lock	the outer lock object

Throws

NullPointerException	if the lock is null

Public Methods

public int getHoldCount ()

Queries the number of holds on this write lock by the current thread. A thread has a hold on a lock for each lock action that is not matched by an unlock action. Identical in effect to ReentrantReadWriteLock.getWriteHoldCount().

Returns

• the number of holds on this lock by the current thread, or zero if this lock is not held by the current thread

public boolean isHeldByCurrentThread ()

Queries if this write lock is held by the current thread. Identical in effect to ReentrantReadWriteLock.isWriteLockedByCurrentThread().

Returns

• true if the current thread holds this lock and false otherwise

public void lock ()

Acquires the write lock.

Acquires the write lock if neither the read nor write lock are held by another thread and returns immediately, setting the write lock hold count to one.

If the current thread already holds the write lock then the hold count is incremented by one and the method returns immediately.

If the lock is held by another thread then the current thread becomes disabled for thread scheduling purposes and lies dormant until the write lock has been acquired, at which time the write lock hold count is set to one.

public void lockInterruptibly ()

Acquires the write lock unless the current thread is {@linkplain Thread#interrupt interrupted}.

Acquires the write lock if neither the read nor write lock are held by another thread and returns immediately, setting the write lock hold count to one.

If the current thread already holds this lock then the hold count is incremented by one and the method returns immediately.

If the lock is held by another thread then the current thread becomes disabled for thread scheduling purposes and lies dormant until one of two things happens:

• The write lock is acquired by the current thread; or
• Some other thread {@linkplain Thread#interrupt interrupts} the current thread.

If the write lock is acquired by the current thread then the lock hold count is set to one.

If the current thread:

• has its interrupted status set on entry to this method; or
• is {@linkplain Thread#interrupt interrupted} while acquiring the write lock,

then InterruptedException is thrown and the current thread's interrupted status is cleared.

In this implementation, as this method is an explicit interruption point, preference is given to responding to the interrupt over normal or reentrant acquisition of the lock.

Throws

InterruptedException	if the current thread is interrupted

public Condition newCondition ()

Returns a Condition instance for use with this Lock instance.

The returned Condition instance supports the same usages as do the Object monitor methods (wait, notify, and notifyAll) when used with the built-in monitor lock.

• If this write lock is not held when any Condition method is called then an IllegalMonitorStateException is thrown. (Read locks are held independently of write locks, so are not checked or affected. However it is essentially always an error to invoke a condition waiting method when the current thread has also acquired read locks, since other threads that could unblock it will not be able to acquire the write lock.)
• When the condition {@linkplain Condition#await() waiting} methods are called the write lock is released and, before they return, the write lock is reacquired and the lock hold count restored to what it was when the method was called.
• If a thread is {@linkplain Thread#interrupt interrupted} while waiting then the wait will terminate, an InterruptedException will be thrown, and the thread's interrupted status will be cleared.
• Waiting threads are signalled in FIFO order.
• The ordering of lock reacquisition for threads returning from waiting methods is the same as for threads initially acquiring the lock, which is in the default case not specified, but for fair locks favors those threads that have been waiting the longest.

Returns

• the Condition object

public String toString ()

Returns a string identifying this lock, as well as its lock state. The state, in brackets includes either the String "Unlocked" or the String "Locked by" followed by the {@linkplain Thread#getName name} of the owning thread.

Returns

• a string identifying this lock, as well as its lock state

public boolean tryLock ()

Acquires the write lock only if it is not held by another thread at the time of invocation.

Acquires the write lock if neither the read nor write lock are held by another thread and returns immediately with the value true, setting the write lock hold count to one. Even when this lock has been set to use a fair ordering policy, a call to tryLock() will immediately acquire the lock if it is available, whether or not other threads are currently waiting for the write lock. This "barging" behavior can be useful in certain circumstances, even though it breaks fairness. If you want to honor the fairness setting for this lock, then use tryLock(0, TimeUnit.SECONDS) which is almost equivalent (it also detects interruption).

If the current thread already holds this lock then the hold count is incremented by one and the method returns true.

If the lock is held by another thread then this method will return immediately with the value false.

Returns

• true if the lock was free and was acquired by the current thread, or the write lock was already held by the current thread; and false otherwise.

public boolean tryLock (long timeout, TimeUnit unit)

Acquires the write lock if it is not held by another thread within the given waiting time and the current thread has not been {@linkplain Thread#interrupt interrupted}.

Acquires the write lock if neither the read nor write lock are held by another thread and returns immediately with the value true, setting the write lock hold count to one. If this lock has been set to use a fair ordering policy then an available lock will not be acquired if any other threads are waiting for the write lock. This is in contrast to the tryLock() method. If you want a timed tryLock that does permit barging on a fair lock then combine the timed and un-timed forms together:

 if (lock.tryLock() ||
     lock.tryLock(timeout, unit)) {
   ...
 }

If the current thread already holds this lock then the hold count is incremented by one and the method returns true.

If the lock is held by another thread then the current thread becomes disabled for thread scheduling purposes and lies dormant until one of three things happens:

• The write lock is acquired by the current thread; or
• Some other thread {@linkplain Thread#interrupt interrupts} the current thread; or
• The specified waiting time elapses

If the write lock is acquired then the value true is returned and the write lock hold count is set to one.

If the current thread:

• has its interrupted status set on entry to this method; or
• is {@linkplain Thread#interrupt interrupted} while acquiring the write lock,

then InterruptedException is thrown and the current thread's interrupted status is cleared.

If the specified waiting time elapses then the value false is returned. If the time is less than or equal to zero, the method will not wait at all.

In this implementation, as this method is an explicit interruption point, preference is given to responding to the interrupt over normal or reentrant acquisition of the lock, and over reporting the elapse of the waiting time.

Parameters

timeout	the time to wait for the write lock
unit	the time unit of the timeout argument

Returns

• true if the lock was free and was acquired by the current thread, or the write lock was already held by the current thread; and false if the waiting time elapsed before the lock could be acquired.

Throws

InterruptedException	if the current thread is interrupted
NullPointerException	if the time unit is null

public void unlock ()

Attempts to release this lock.

If the current thread is the holder of this lock then the hold count is decremented. If the hold count is now zero then the lock is released. If the current thread is not the holder of this lock then IllegalMonitorStateException is thrown.

Throws

IllegalMonitorStateException	if the current thread does not hold this lock