ReentrantReadWriteLock.ReadLock (Java 2 Platform SE 5.0) (original) (raw)

java.util.concurrent.locks

Class ReentrantReadWriteLock.ReadLock

java.lang.Object java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock

All Implemented Interfaces:

Serializable, Lock

Enclosing class:

ReentrantReadWriteLock

public static class ReentrantReadWriteLock.ReadLock

extends Object

implements Lock, Serializable

The lock returned by method ReentrantReadWriteLock.readLock().

See Also:

Serialized Form

ReentrantReadWriteLock.ReadLock

protected ReentrantReadWriteLock.ReadLock(ReentrantReadWriteLock lock)

Constructor for use by subclasses

Parameters:

lock - the outer lock object

Throws:

[NullPointerException](../../../../java/lang/NullPointerException.html "class in java.lang") - if lock null

lock

public void lock()

Acquires the read lock.

Acquires the read lock if the write lock is not held by another thread and returns immediately.

If the write lock is held by another thread then the current thread becomes disabled for thread scheduling purposes and lies dormant until the read lock has been acquired.

Specified by:

[lock](../../../../java/util/concurrent/locks/Lock.html#lock%28%29) in interface [Lock](../../../../java/util/concurrent/locks/Lock.html "interface in java.util.concurrent.locks")

lockInterruptibly

public void lockInterruptibly() throws InterruptedException

Acquires the read lock unless the current thread is interrupted.

Acquires the read lock if the write lock is not held by another thread and returns immediately.

If the write 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 read lock is acquired by the current thread; or
• Some other thread interrupts the current thread.

If the current thread:

• has its interrupted status set on entry to this method; or
• is interrupted while acquiring the read 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](../../../../java/util/concurrent/locks/Lock.html#lockInterruptibly%28%29) in interface [Lock](../../../../java/util/concurrent/locks/Lock.html "interface in java.util.concurrent.locks")

Throws:

[InterruptedException](../../../../java/lang/InterruptedException.html "class in java.lang") - if the current thread is interrupted

See Also:

Thread.interrupt()

tryLock

public boolean tryLock()

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

Acquires the read lock if the write lock is not held by another thread and returns immediately with the valuetrue. Even when this lock has been set to use a fair ordering policy, a call to tryLock() will immediately acquire the read lock if it is available, whether or not other threads are currently waiting for the read 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) ](../../../../java/util/concurrent/locks/ReentrantReadWriteLock.ReadLock.html#tryLock%28long, java.util.concurrent.TimeUnit%29) which is almost equivalent (it also detects interruption).

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

Specified by:

[tryLock](../../../../java/util/concurrent/locks/Lock.html#tryLock%28%29) in interface [Lock](../../../../java/util/concurrent/locks/Lock.html "interface in java.util.concurrent.locks")

Returns:

true if the read lock was acquired.

tryLock

public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException

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

Acquires the read lock if the write lock is not held by another thread and returns immediately with the valuetrue. 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 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 write 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 read lock is acquired by the current thread; or
• Some other thread interrupts the current thread; or
• The specified waiting time elapses

If the read lock is acquired then the value true is returned.

If the current thread:

• has its interrupted status set on entry to this method; or
• is interrupted while acquiring the read lock, then InterruptedException is thrown and the current thread's interrupted status is cleared.

If the specified waiting time elapses then the valuefalse 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](../../../../java/util/concurrent/locks/Lock.html#tryLock%28long, java.util.concurrent.TimeUnit%29) in interface [Lock](../../../../java/util/concurrent/locks/Lock.html "interface in java.util.concurrent.locks")

Parameters:

timeout - the time to wait for the read lock

unit - the time unit of the timeout argument

Returns:

true if the read lock was acquired.

Throws:

[InterruptedException](../../../../java/lang/InterruptedException.html "class in java.lang") - if the current thread is interrupted

[NullPointerException](../../../../java/lang/NullPointerException.html "class in java.lang") - if unit is null

See Also:

Thread.interrupt()

unlock

public void unlock()

Attempts to release this lock.

If the number of readers is now zero then the lock is made available for write lock attempts.

Specified by:

[unlock](../../../../java/util/concurrent/locks/Lock.html#unlock%28%29) in interface [Lock](../../../../java/util/concurrent/locks/Lock.html "interface in java.util.concurrent.locks")

newCondition

public Condition newCondition()

Throws UnsupportedOperationException becauseReadLocks do not support conditions.

Specified by:

[newCondition](../../../../java/util/concurrent/locks/Lock.html#newCondition%28%29) in interface [Lock](../../../../java/util/concurrent/locks/Lock.html "interface in java.util.concurrent.locks")

Returns:

A new Condition instance for this Lock instance.

Throws:

[UnsupportedOperationException](../../../../java/lang/UnsupportedOperationException.html "class in java.lang") - always

toString

public String toString()

Returns a string identifying this lock, as well as its lock state. The state, in brackets, includes the String "Read locks =" followed by the number of held read locks.

Overrides:

[toString](../../../../java/lang/Object.html#toString%28%29) in class [Object](../../../../java/lang/Object.html "class in java.lang")

Returns:

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

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