AbstractQueuedLongSynchronizer

AbstractQueuedLongSynchronizer

AbstractQueuedLongSynchronizer ()

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

acquire

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().

acquireInterruptibly

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 lockInterruptibly().

acquireShared

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.

acquireSharedInterruptibly

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.

getExclusiveQueuedThreads

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.

getFirstQueuedThread

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.

getQueueLength

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.

getQueuedThreads

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.

getSharedQueuedThreads

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.

getWaitQueueLength

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.

getWaitingThreads

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.

hasContended

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.

hasQueuedPredecessors

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
   }
 }

hasQueuedThreads

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.

hasWaiters

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.

isQueued

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.

owns

boolean owns (AbstractQueuedLongSynchronizer.ConditionObject condition)

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

release

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 unlock().

releaseShared

boolean releaseShared (long arg)

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

toString

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.

tryAcquireNanos

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 tryLock(long, TimeUnit).

tryAcquireSharedNanos

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.

compareAndSetState

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.

getState

long getState ()

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

isHeldExclusively

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.

setState

void setState (long newState)

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

tryAcquire

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 tryLock().

The default implementation throws UnsupportedOperationException.

tryAcquireShared

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.

tryRelease

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.

tryReleaseShared

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.