edu.emory.mathcs.backport.java.util.concurrent.locks

Class ReentrantReadWriteLock.WriteLock

Enclosing Class:
ReentrantReadWriteLock
Implemented Interfaces:
edu.emory.mathcs.backport.java.util.concurrent.locks.CondVar.ExclusiveLock, Lock, java.io.Serializable

public static class ReentrantReadWriteLock.WriteLock
extends java.lang.Object
implements Lock, edu.emory.mathcs.backport.java.util.concurrent.locks.CondVar.ExclusiveLock, java.io.Serializable

The lock returned by method ReentrantReadWriteLock.writeLock().
See Also:
Serialized Form

Constructor Summary

WriteLock(ReentrantReadWriteLock lock)
Constructor for use by subclasses

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 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 interrupted.
void
unlock()
Attempts to release this lock.

Constructor Details

WriteLock

protected WriteLock(ReentrantReadWriteLock lock)
Constructor for use by subclasses
Parameters:
lock - the outer lock object

Method Details

getHoldCount

public int getHoldCount()
Specified by:
getHoldCount in interface edu.emory.mathcs.backport.java.util.concurrent.locks.CondVar.ExclusiveLock
Returns:
the number of holds on this lock by the current thread, or zero if this lock is not held by the current thread
Since:
1.6

isHeldByCurrentThread

public boolean isHeldByCurrentThread()
Specified by:
isHeldByCurrentThread in interface edu.emory.mathcs.backport.java.util.concurrent.locks.CondVar.ExclusiveLock
Returns:
true if the current thread holds this lock and false otherwise
Since:
1.6

lock

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.

Specified by:
lock in interface Lock

lockInterruptibly

public void lockInterruptibly()
            throws InterruptedException
Acquires the write lock unless the current thread is 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 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 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.

Specified by:
lockInterruptibly in interface Lock

newCondition

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 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 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.
Specified by:
newCondition in interface Lock
Returns:
the Condition object

toString

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 name of the owning thread.
Returns:
a string identifying this lock, as well as its lock state

tryLock

public boolean tryLock()
Specified by:
tryLock in interface Lock
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.

tryLock

public boolean tryLock(long timeout,
                       TimeUnit unit)
            throws InterruptedException
Acquires the write lock if it is not held by another thread within the given waiting time and the current thread has not been 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 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 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.

Specified by:
tryLock in interface 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 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.

unlock

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.

Specified by:
unlock in interface Lock