AbstractQueuedLongSynchronizer

  • AbstractQueuedLongSynchronizer manages synchronization state as a long, enabling complex locking scenarios like multilevel locks and barriers.

  • It provides methods for exclusive and shared acquisition, supporting thread queuing and condition waiting with ConditionObject.

  • Subclasses implement protected methods like tryAcquire and tryRelease to define custom synchronization behavior.

  • Public methods like acquire, release, and hasQueuedThreads offer external control over the synchronizer.

  • AbstractQueuedLongSynchronizer extends AbstractOwnableSynchronizer for exclusive ownership and implements Serializable for persistence.
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.

Nested Class Summary

class AbstractQueuedLongSynchronizer.ConditionObject Condition implementation for a AbstractQueuedLongSynchronizer serving as the basis of a Lock implementation. 

Protected Constructor Summary

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

Public Method Summary

final void
acquire(long arg)
Acquires in exclusive mode, ignoring interrupts.
final void
acquireInterruptibly(long arg)
Acquires in exclusive mode, aborting if interrupted.
final void
acquireShared(long arg)
Acquires in shared mode, ignoring interrupts.
final void
acquireSharedInterruptibly(long arg)
Acquires in shared mode, aborting if interrupted.
final Collection<Thread>
getExclusiveQueuedThreads()
Returns a collection containing threads that may be waiting to acquire in exclusive mode.
final Thread
getFirstQueuedThread()
Returns the first (longest-waiting) thread in the queue, or null if no threads are currently queued.
final int
getQueueLength()
Returns an estimate of the number of threads waiting to acquire.
final Collection<Thread>
getQueuedThreads()
Returns a collection containing threads that may be waiting to acquire.
final Collection<Thread>
getSharedQueuedThreads()
Returns a collection containing threads that may be waiting to acquire in shared mode.
final int
getWaitQueueLength(AbstractQueuedLongSynchronizer.ConditionObject condition)
Returns an estimate of the number of threads waiting on the given condition associated with this synchronizer.
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.
final boolean
hasContended()
Queries whether any threads have ever contended to acquire this synchronizer; that is, if an acquire method has ever blocked.
final boolean
hasQueuedPredecessors()
Queries whether any threads have been waiting to acquire longer than the current thread.
final boolean
hasQueuedThreads()
Queries whether any threads are waiting to acquire.
final boolean
hasWaiters(AbstractQueuedLongSynchronizer.ConditionObject condition)
Queries whether any threads are waiting on the given condition associated with this synchronizer.
final boolean
isQueued(Thread thread)
Returns true if the given thread is currently queued.
final boolean
owns(AbstractQueuedLongSynchronizer.ConditionObject condition)
Queries whether the given ConditionObject uses this synchronizer as its lock.
final boolean
release(long arg)
Releases in exclusive mode.
final boolean
releaseShared(long arg)
Releases in shared mode.
String
toString()
Returns a string identifying this synchronizer, as well as its state.
final boolean
tryAcquireNanos(long arg, long nanosTimeout)
Attempts to acquire in exclusive mode, aborting if interrupted, and failing if the given timeout elapses.
final boolean
tryAcquireSharedNanos(long arg, long nanosTimeout)
Attempts to acquire in shared mode, aborting if interrupted, and failing if the given timeout elapses.

Protected Method Summary

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.
final long
getState()
Returns the current value of synchronization state.
boolean
isHeldExclusively()
Returns true if synchronization is held exclusively with respect to the current (calling) thread.
final void
setState(long newState)
Sets the value of synchronization state.
boolean
tryAcquire(long arg)
Attempts to acquire in exclusive mode.
long
tryAcquireShared(long arg)
Attempts to acquire in shared mode.
boolean
tryRelease(long arg)
Attempts to set the state to reflect a release in exclusive mode.
boolean
tryReleaseShared(long arg)
Attempts to set the state to reflect a release in shared mode.

Inherited Method Summary

Protected Constructors

protected AbstractQueuedLongSynchronizer ()

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

Public Methods

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.

public final void acquireInterruptibly (long arg)

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

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.

public final void acquireSharedInterruptibly (long arg)

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

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

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

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

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

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

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 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

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

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

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

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

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

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

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

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

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

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.

Returns
  • a string identifying this synchronizer, as well as its state

public final boolean tryAcquireNanos (long arg, long nanosTimeout)

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

public final boolean tryAcquireSharedNanos (long arg, long nanosTimeout)

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

Protected Methods

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.

protected final long getState ()

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

Returns
  • current state value

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

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

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

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

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

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