co.paralleluniverse.strands.concurrent

Class ReentrantReadWriteLock.WriteLock

java.lang.Object

co.paralleluniverse.strands.concurrent.ReentrantReadWriteLock.WriteLock

All Implemented Interfaces:

java.io.Serializable, java.util.concurrent.locks.Lock

Enclosing class:

ReentrantReadWriteLock

public static class ReentrantReadWriteLock.WriteLock
extends java.lang.Object
implements java.util.concurrent.locks.Lock, java.io.Serializable

The lock returned by method ReentrantReadWriteLock.writeLock().

See Also:

Serialized Form

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	WriteLock(ReentrantReadWriteLock lock) Constructor for use by subclasses

Method Summary

Modifier and Type	Method and Description
int	getHoldCount() Queries the number of holds on this write lock by the current strand.
boolean	isHeldByCurrentStrand() Queries if this write lock is held by the current strand.
void	lock() Acquires the write lock.
void	lockInterruptibly() Acquires the write lock unless the current strand is interrupted.
java.util.concurrent.locks.Condition	newCondition() Returns a Condition instance for use with this Lock instance.
java.lang.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 strand at the time of invocation.
boolean	tryLock(long timeout, java.util.concurrent.TimeUnit unit) Acquires the write lock if it is not held by another strand within the given waiting time and the current strand has not been interrupted.
void	unlock() Attempts to release this lock.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

WriteLock

protected WriteLock(ReentrantReadWriteLock lock)

Constructor for use by subclasses

Parameters:

lock - the outer lock object

Throws:

java.lang.NullPointerException - if the lock is null

Method Detail

lock

@Suspendable
public void lock()

Acquires the write lock.

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

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

Specified by:

lock in interface java.util.concurrent.locks.Lock

lockInterruptibly

@Suspendable
public void lockInterruptibly()
                                    throws java.lang.InterruptedException

Acquires the write lock unless the current strand is interrupted.

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

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

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

• The write lock is acquired by the current strand; or
• Some other strand interrupts the current strand.

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

If the current strand:

• has its interrupted status set on entry to this method; or
• is interrupted while acquiring the write lock,

then InterruptedException is thrown and the current strand'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.

Specified by:

lockInterruptibly in interface java.util.concurrent.locks.Lock

Throws:

java.lang.InterruptedException - if the current strand is interrupted

tryLock

public boolean tryLock()

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

Acquires the write lock if neither the read nor write lock are held by another strand 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 strands 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 strand already holds this lock then the hold count is incremented by one and the method returns true.

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

Specified by:

tryLock in interface java.util.concurrent.locks.Lock

Returns:

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

tryLock

@Suspendable
public boolean tryLock(long timeout,
                                    java.util.concurrent.TimeUnit unit)
                             throws java.lang.InterruptedException

Acquires the write lock if it is not held by another strand within the given waiting time and the current strand has not been interrupted.

Acquires the write lock if neither the read nor write lock are held by another strand 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 strands 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 strand already holds this lock then the hold count is incremented by one and the method returns true.

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

• The write lock is acquired by the current strand; or
• Some other strand interrupts the current strand; 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 strand:

• has its interrupted status set on entry to this method; or
• is interrupted while acquiring the write lock,

then InterruptedException is thrown and the current strand'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.

Specified by:

tryLock in interface java.util.concurrent.locks.Lock

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

Throws:

java.lang.InterruptedException - if the current strand is interrupted

java.lang.NullPointerException - if the time unit is null

unlock

public void unlock()

Attempts to release this lock.

If the current strand 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 strand is not the holder of this lock then IllegalMonitorStateException is thrown.

Specified by:

unlock in interface java.util.concurrent.locks.Lock

Throws:

java.lang.IllegalMonitorStateException - if the current strand does not hold this lock.

newCondition

public java.util.concurrent.locks.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 strand has also acquired read locks, since other strands that could unblock it will not be able to acquire the write lock.)
• When the condition 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 strand is interrupted while waiting then the wait will terminate, an InterruptedException will be thrown, and the strand's interrupted status will be cleared.
• Waiting strands are signalled in FIFO order.
• The ordering of lock reacquisition for strands returning from waiting methods is the same as for strands initially acquiring the lock, which is in the default case not specified, but for fair locks favors those strands that have been waiting the longest.

Specified by:

newCondition in interface java.util.concurrent.locks.Lock

Returns:

the Condition object

toString

public java.lang.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 name of the owning strand.

Overrides:

toString in class java.lang.Object

Returns:

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

isHeldByCurrentStrand

public boolean isHeldByCurrentStrand()

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

Returns:

true if the current strand holds this lock and false otherwise

Since:

1.6

getHoldCount

public int getHoldCount()

Queries the number of holds on this write lock by the current strand. A strand 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 strand, or zero if this lock is not held by the current strand

Since:

1.6