co.paralleluniverse.strands.concurrent

Class ReentrantReadWriteLock.ReadLock

java.lang.Object

co.paralleluniverse.strands.concurrent.ReentrantReadWriteLock.ReadLock

All Implemented Interfaces:

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

Enclosing class:

ReentrantReadWriteLock

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

The lock returned by method ReentrantReadWriteLock.readLock().

See Also:

Serialized Form

Constructor Summary

Constructors

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

Method Summary

Modifier and Type	Method and Description
void	lock() Acquires the read lock.
void	lockInterruptibly() Acquires the read lock unless the current strand is interrupted.
java.util.concurrent.locks.Condition	newCondition() Throws UnsupportedOperationException because ReadLocks do not support conditions.
java.lang.String	toString() Returns a string identifying this lock, as well as its lock state.
boolean	tryLock() Acquires the read lock only if the write lock is not held by another strand at the time of invocation.
boolean	tryLock(long timeout, java.util.concurrent.TimeUnit unit) Acquires the read lock if the write lock 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

ReadLock

protected ReadLock(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 read lock.

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

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

Specified by:

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

lockInterruptibly

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

Acquires the read lock unless the current strand is interrupted.

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

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

If the current strand:

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

Acquires the read lock if the write lock is not held by another strand and returns immediately with the value true. 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 strands 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) which is almost equivalent (it also detects interruption).

If the write 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 read lock was acquired

tryLock

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

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

Acquires the read lock if the write lock is not held by another strand and returns immediately with the value true. 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 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 strand then the current strand becomes disabled for strand scheduling purposes and lies dormant until one of three things happens:

• The read lock is acquired by the current strand; or
• Some other strand interrupts the current strand; or
• The specified waiting time elapses.

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

If the current strand:

• 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 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 read lock

unit - the time unit of the timeout argument

Returns:

true if the read lock was 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 number of readers is now zero then the lock is made available for write lock attempts.

Specified by:

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

newCondition

public java.util.concurrent.locks.Condition newCondition()

Throws UnsupportedOperationException because ReadLocks do not support conditions.

Specified by:

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

Throws:

java.lang.UnsupportedOperationException - always

toString

public java.lang.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 in class java.lang.Object

Returns:

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