java.util.concurrent.locks

Class AbstractQueuedLongSynchronizer

java.lang.Object

java.util.concurrent.locks.AbstractOwnableSynchronizer

java.util.concurrent.locks.AbstractQueuedLongSynchronizer

All Implemented Interfaces:

Serializable

public abstract class AbstractQueuedLongSynchronizer
extends AbstractOwnableSynchronizer
implements Serializable

A version of AbstractQueuedSynchronizer in which synchronization state is maintained as a long. This class has exactly the same structure, properties, and methods as AbstractQueuedSynchronizer with the exception that all state-related parameters and results are defined as long rather than int. This class may be useful when creating synchronizers such as multilevel locks and barriers that require 64 bits of state.

See AbstractQueuedSynchronizer for usage notes and examples.

Since:

1.6

Author:

Doug Lea

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	AbstractQueuedLongSynchronizer.ConditionObject Condition implementation for a AbstractQueuedLongSynchronizer serving as the basis of a Lock implementation.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	AbstractQueuedLongSynchronizer() Creates a new AbstractQueuedLongSynchronizer instance with initial synchronization state of zero.

Method Summary

Methods

Modifier and Type	Method and Description
void	acquire(long arg) Acquires in exclusive mode, ignoring interrupts.
void	acquireInterruptibly(long arg) Acquires in exclusive mode, aborting if interrupted.
void	acquireShared(long arg) Acquires in shared mode, ignoring interrupts.
void	acquireSharedInterruptibly(long arg) Acquires in shared mode, aborting if interrupted.
protected boolean	compareAndSetState(long expect, long update) Atomically sets synchronization state to the given updated value if the current state value equals the expected value.
Collection<Thread>	getExclusiveQueuedThreads() Returns a collection containing threads that may be waiting to acquire in exclusive mode.
Thread	getFirstQueuedThread() Returns the first (longest-waiting) thread in the queue, or null if no threads are currently queued.
Collection<Thread>	getQueuedThreads() Returns a collection containing threads that may be waiting to acquire.
int	getQueueLength() Returns an estimate of the number of threads waiting to acquire.
Collection<Thread>	getSharedQueuedThreads() Returns a collection containing threads that may be waiting to acquire in shared mode.
protected long	getState() Returns the current value of synchronization state.
Collection<Thread>	getWaitingThreads(AbstractQueuedLongSynchronizer.ConditionObject condition) Returns a collection containing those threads that may be waiting on the given condition associated with this synchronizer.
int	getWaitQueueLength(AbstractQueuedLongSynchronizer.ConditionObject condition) Returns an estimate of the number of threads waiting on the given condition associated with this synchronizer.
boolean	hasContended() Queries whether any threads have ever contended to acquire this synchronizer; that is if an acquire method has ever blocked.
boolean	hasQueuedPredecessors() Queries whether any threads have been waiting to acquire longer than the current thread.
boolean	hasQueuedThreads() Queries whether any threads are waiting to acquire.
boolean	hasWaiters(AbstractQueuedLongSynchronizer.ConditionObject condition) Queries whether any threads are waiting on the given condition associated with this synchronizer.
protected boolean	isHeldExclusively() Returns true if synchronization is held exclusively with respect to the current (calling) thread.
boolean	isQueued(Thread thread) Returns true if the given thread is currently queued.
boolean	owns(AbstractQueuedLongSynchronizer.ConditionObject condition) Queries whether the given ConditionObject uses this synchronizer as its lock.
boolean	release(long arg) Releases in exclusive mode.
boolean	releaseShared(long arg) Releases in shared mode.
protected void	setState(long newState) Sets the value of synchronization state.
String	toString() Returns a string identifying this synchronizer, as well as its state.
protected boolean	tryAcquire(long arg) Attempts to acquire in exclusive mode.
boolean	tryAcquireNanos(long arg, long nanosTimeout) Attempts to acquire in exclusive mode, aborting if interrupted, and failing if the given timeout elapses.
protected long	tryAcquireShared(long arg) Attempts to acquire in shared mode.
boolean	tryAcquireSharedNanos(long arg, long nanosTimeout) Attempts to acquire in shared mode, aborting if interrupted, and failing if the given timeout elapses.
protected boolean	tryRelease(long arg) Attempts to set the state to reflect a release in exclusive mode.
protected boolean	tryReleaseShared(long arg) Attempts to set the state to reflect a release in shared mode.

Methods inherited from class java.util.concurrent.locks.AbstractOwnableSynchronizer

getExclusiveOwnerThread, setExclusiveOwnerThread

Methods inherited from class java.lang.Object

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

Constructor Detail

AbstractQueuedLongSynchronizer

protected AbstractQueuedLongSynchronizer()

Creates a new AbstractQueuedLongSynchronizer instance with initial synchronization state of zero.

Method Detail

getState

protected final long getState()

Returns the current value of synchronization state. This operation has memory semantics of a volatile read.

Returns:

current state value

setState

protected final void setState(long newState)

Sets the value of synchronization state. This operation has memory semantics of a volatile write.

Parameters:

newState - the new state value

compareAndSetState

protected final boolean compareAndSetState(long expect,
                         long update)

Atomically sets synchronization state to the given updated value if the current state value equals the expected value. This operation has memory semantics of a volatile read and write.

Parameters:

expect - the expected value

update - the new value

Returns:

true if successful. False return indicates that the actual value was not equal to the expected value.

tryAcquire

protected boolean tryAcquire(long arg)

Attempts to acquire in exclusive mode. This method should query if the state of the object permits it to be acquired in the exclusive mode, and if so to acquire it.

This method is always invoked by the thread performing acquire. If this method reports failure, the acquire method may queue the thread, if it is not already queued, until it is signalled by a release from some other thread. This can be used to implement method Lock.tryLock().

The default implementation throws UnsupportedOperationException.

Parameters:

arg - the acquire argument. This value is always the one passed to an acquire method, or is the value saved on entry to a condition wait. The value is otherwise uninterpreted and can represent anything you like.

Returns:

true if successful. Upon success, this object has been acquired.

Throws:

IllegalMonitorStateException - if acquiring would place this synchronizer in an illegal state. This exception must be thrown in a consistent fashion for synchronization to work correctly.

UnsupportedOperationException - if exclusive mode is not supported

tryRelease

protected boolean tryRelease(long arg)

Attempts to set the state to reflect a release in exclusive mode.

This method is always invoked by the thread performing release.

The default implementation throws UnsupportedOperationException.

Parameters:

arg - the release argument. This value is always the one passed to a release method, or the current state value upon entry to a condition wait. The value is otherwise uninterpreted and can represent anything you like.

Returns:

true if this object is now in a fully released state, so that any waiting threads may attempt to acquire; and false otherwise.

Throws:

IllegalMonitorStateException - if releasing would place this synchronizer in an illegal state. This exception must be thrown in a consistent fashion for synchronization to work correctly.

UnsupportedOperationException - if exclusive mode is not supported

tryAcquireShared

protected long tryAcquireShared(long arg)

Attempts to acquire in shared mode. This method should query if the state of the object permits it to be acquired in the shared mode, and if so to acquire it.

This method is always invoked by the thread performing acquire. If this method reports failure, the acquire method may queue the thread, if it is not already queued, until it is signalled by a release from some other thread.

The default implementation throws UnsupportedOperationException.

Parameters:

arg - the acquire argument. This value is always the one passed to an acquire method, or is the value saved on entry to a condition wait. The value is otherwise uninterpreted and can represent anything you like.

Returns:

a negative value on failure; zero if acquisition in shared mode succeeded but no subsequent shared-mode acquire can succeed; and a positive value if acquisition in shared mode succeeded and subsequent shared-mode acquires might also succeed, in which case a subsequent waiting thread must check availability. (Support for three different return values enables this method to be used in contexts where acquires only sometimes act exclusively.) Upon success, this object has been acquired.

Throws:

IllegalMonitorStateException - if acquiring would place this synchronizer in an illegal state. This exception must be thrown in a consistent fashion for synchronization to work correctly.

UnsupportedOperationException - if shared mode is not supported

tryReleaseShared

protected boolean tryReleaseShared(long arg)

Attempts to set the state to reflect a release in shared mode.

This method is always invoked by the thread performing release.

The default implementation throws UnsupportedOperationException.

Parameters:

arg - the release argument. This value is always the one passed to a release method, or the current state value upon entry to a condition wait. The value is otherwise uninterpreted and can represent anything you like.

Returns:

true if this release of shared mode may permit a waiting acquire (shared or exclusive) to succeed; and false otherwise

Throws:

IllegalMonitorStateException - if releasing would place this synchronizer in an illegal state. This exception must be thrown in a consistent fashion for synchronization to work correctly.

UnsupportedOperationException - if shared mode is not supported

isHeldExclusively

protected boolean isHeldExclusively()

Returns true if synchronization is held exclusively with respect to the current (calling) thread. This method is invoked upon each call to a non-waiting AbstractQueuedLongSynchronizer.ConditionObject method. (Waiting methods instead invoke release(long).)

The default implementation throws UnsupportedOperationException. This method is invoked internally only within AbstractQueuedLongSynchronizer.ConditionObject methods, so need not be defined if conditions are not used.

Returns:

true if synchronization is held exclusively; false otherwise

Throws:

UnsupportedOperationException - if conditions are not supported

acquire

public final void acquire(long arg)

Acquires in exclusive mode, ignoring interrupts. Implemented by invoking at least once tryAcquire(long), returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquire(long) until success. This method can be used to implement method Lock.lock().

Parameters:

arg - the acquire argument. This value is conveyed to tryAcquire(long) but is otherwise uninterpreted and can represent anything you like.

acquireInterruptibly

public final void acquireInterruptibly(long arg)
                                throws InterruptedException

Acquires in exclusive mode, aborting if interrupted. Implemented by first checking interrupt status, then invoking at least once tryAcquire(long), returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquire(long) until success or the thread is interrupted. This method can be used to implement method Lock.lockInterruptibly().

Parameters:

arg - the acquire argument. This value is conveyed to tryAcquire(long) but is otherwise uninterpreted and can represent anything you like.

Throws:

InterruptedException - if the current thread is interrupted

tryAcquireNanos

public final boolean tryAcquireNanos(long arg,
                      long nanosTimeout)
                              throws InterruptedException

Attempts to acquire in exclusive mode, aborting if interrupted, and failing if the given timeout elapses. Implemented by first checking interrupt status, then invoking at least once tryAcquire(long), returning on success. Otherwise, the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquire(long) until success or the thread is interrupted or the timeout elapses. This method can be used to implement method Lock.tryLock(long, TimeUnit).

Parameters:

arg - the acquire argument. This value is conveyed to tryAcquire(long) but is otherwise uninterpreted and can represent anything you like.

nanosTimeout - the maximum number of nanoseconds to wait

Returns:

true if acquired; false if timed out

Throws:

InterruptedException - if the current thread is interrupted

release

public final boolean release(long arg)

Releases in exclusive mode. Implemented by unblocking one or more threads if tryRelease(long) returns true. This method can be used to implement method Lock.unlock().

Parameters:

arg - the release argument. This value is conveyed to tryRelease(long) but is otherwise uninterpreted and can represent anything you like.

Returns:

the value returned from tryRelease(long)

acquireShared

public final void acquireShared(long arg)

Acquires in shared mode, ignoring interrupts. Implemented by first invoking at least once tryAcquireShared(long), returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquireShared(long) until success.

Parameters:

arg - the acquire argument. This value is conveyed to tryAcquireShared(long) but is otherwise uninterpreted and can represent anything you like.

acquireSharedInterruptibly

public final void acquireSharedInterruptibly(long arg)
                                      throws InterruptedException

Acquires in shared mode, aborting if interrupted. Implemented by first checking interrupt status, then invoking at least once tryAcquireShared(long), returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquireShared(long) until success or the thread is interrupted.

Parameters:

arg - the acquire argument This value is conveyed to tryAcquireShared(long) but is otherwise uninterpreted and can represent anything you like.

Throws:

InterruptedException - if the current thread is interrupted

tryAcquireSharedNanos

public final boolean tryAcquireSharedNanos(long arg,
                            long nanosTimeout)
                                    throws InterruptedException

Attempts to acquire in shared mode, aborting if interrupted, and failing if the given timeout elapses. Implemented by first checking interrupt status, then invoking at least once tryAcquireShared(long), returning on success. Otherwise, the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquireShared(long) until success or the thread is interrupted or the timeout elapses.

Parameters:

arg - the acquire argument. This value is conveyed to tryAcquireShared(long) but is otherwise uninterpreted and can represent anything you like.

nanosTimeout - the maximum number of nanoseconds to wait

Returns:

true if acquired; false if timed out

Throws:

InterruptedException - if the current thread is interrupted

releaseShared

public final boolean releaseShared(long arg)

Releases in shared mode. Implemented by unblocking one or more threads if tryReleaseShared(long) returns true.

Parameters:

arg - the release argument. This value is conveyed to tryReleaseShared(long) but is otherwise uninterpreted and can represent anything you like.

Returns:

the value returned from tryReleaseShared(long)

hasQueuedThreads

public final boolean hasQueuedThreads()

Queries whether any threads are waiting to acquire. Note that because cancellations due to interrupts and timeouts may occur at any time, a true return does not guarantee that any other thread will ever acquire.

In this implementation, this operation returns in constant time.

Returns:

true if there may be other threads waiting to acquire

hasContended

public final boolean hasContended()

Queries whether any threads have ever contended to acquire this synchronizer; that is if an acquire method has ever blocked.

In this implementation, this operation returns in constant time.

Returns:

true if there has ever been contention

getFirstQueuedThread

public final Thread getFirstQueuedThread()

Returns the first (longest-waiting) thread in the queue, or null if no threads are currently queued.

In this implementation, this operation normally returns in constant time, but may iterate upon contention if other threads are concurrently modifying the queue.

Returns:

the first (longest-waiting) thread in the queue, or null if no threads are currently queued

isQueued

public final boolean isQueued(Thread thread)

Returns true if the given thread is currently queued.

This implementation traverses the queue to determine presence of the given thread.

Parameters:

thread - the thread

Returns:

true if the given thread is on the queue

Throws:

NullPointerException - if the thread is null

hasQueuedPredecessors

public final boolean hasQueuedPredecessors()

Queries whether any threads have been waiting to acquire longer than the current thread.

An invocation of this method is equivalent to (but may be more efficient than):

 getFirstQueuedThread() != Thread.currentThread() &&
 hasQueuedThreads()

Note that because cancellations due to interrupts and timeouts may occur at any time, a true return does not guarantee that some other thread will acquire before the current thread. Likewise, it is possible for another thread to win a race to enqueue after this method has returned false, due to the queue being empty.

This method is designed to be used by a fair synchronizer to avoid barging. Such a synchronizer's tryAcquire(long) method should return false, and its tryAcquireShared(long) method should return a negative value, if this method returns true (unless this is a reentrant acquire). For example, the tryAcquire method for a fair, reentrant, exclusive mode synchronizer might look like this:

 protected boolean tryAcquire(int arg) {
   if (isHeldExclusively()) {
     // A reentrant acquire; increment hold count
     return true;
   } else if (hasQueuedPredecessors()) {
     return false;
   } else {
     // try to acquire normally
   }
 }

Returns:

true if there is a queued thread preceding the current thread, and false if the current thread is at the head of the queue or the queue is empty

Since:

1.7

getQueueLength

public final int getQueueLength()

Returns an estimate of the number of threads waiting to acquire. The value is only an estimate because the number of threads may change dynamically while this method traverses internal data structures. This method is designed for use in monitoring system state, not for synchronization control.

Returns:

the estimated number of threads waiting to acquire

getQueuedThreads

public final Collection<Thread> getQueuedThreads()

Returns a collection containing threads that may be waiting to acquire. Because the actual set of threads may change dynamically while constructing this result, the returned collection is only a best-effort estimate. The elements of the returned collection are in no particular order. This method is designed to facilitate construction of subclasses that provide more extensive monitoring facilities.

Returns:

the collection of threads

getExclusiveQueuedThreads

public final Collection<Thread> getExclusiveQueuedThreads()

Returns a collection containing threads that may be waiting to acquire in exclusive mode. This has the same properties as getQueuedThreads() except that it only returns those threads waiting due to an exclusive acquire.

Returns:

the collection of threads

getSharedQueuedThreads

public final Collection<Thread> getSharedQueuedThreads()

Returns a collection containing threads that may be waiting to acquire in shared mode. This has the same properties as getQueuedThreads() except that it only returns those threads waiting due to a shared acquire.

Returns:

the collection of threads

toString

public String toString()

Returns a string identifying this synchronizer, as well as its state. The state, in brackets, includes the String "State =" followed by the current value of getState(), and either "nonempty" or "empty" depending on whether the queue is empty.

Overrides:

toString in class Object

Returns:

a string identifying this synchronizer, as well as its state

owns

public final boolean owns(AbstractQueuedLongSynchronizer.ConditionObject condition)

Queries whether the given ConditionObject uses this synchronizer as its lock.

Parameters:

condition - the condition

Returns:

true if owned

Throws:

NullPointerException - if the condition is null

hasWaiters

public final boolean hasWaiters(AbstractQueuedLongSynchronizer.ConditionObject condition)

Queries whether any threads are waiting on the given condition associated with this synchronizer. Note that because timeouts and interrupts may occur at any time, a true return does not guarantee that a future signal will awaken any threads. This method is designed primarily for use in monitoring of the system state.

Parameters:

condition - the condition

Returns:

true if there are any waiting threads

Throws:

IllegalMonitorStateException - if exclusive synchronization is not held

IllegalArgumentException - if the given condition is not associated with this synchronizer

NullPointerException - if the condition is null

getWaitQueueLength

public final int getWaitQueueLength(AbstractQueuedLongSynchronizer.ConditionObject condition)

Returns an estimate of the number of threads waiting on the given condition associated with this synchronizer. Note that because timeouts and interrupts may occur at any time, the estimate serves only as an upper bound on the actual number of waiters. This method is designed for use in monitoring of the system state, not for synchronization control.

Parameters:

condition - the condition

Returns:

the estimated number of waiting threads

Throws:

IllegalMonitorStateException - if exclusive synchronization is not held

IllegalArgumentException - if the given condition is not associated with this synchronizer

NullPointerException - if the condition is null

getWaitingThreads

public final Collection<Thread> getWaitingThreads(AbstractQueuedLongSynchronizer.ConditionObject condition)

Returns a collection containing those threads that may be waiting on the given condition associated with this synchronizer. Because the actual set of threads may change dynamically while constructing this result, the returned collection is only a best-effort estimate. The elements of the returned collection are in no particular order.

Parameters:

condition - the condition

Returns:

the collection of threads

Throws:

IllegalMonitorStateException - if exclusive synchronization is not held

IllegalArgumentException - if the given condition is not associated with this synchronizer

NullPointerException - if the condition is null