java.util.concurrent.locks
Class AbstractQueuedSynchronizer

java.lang.Object sample code for java.lang.Object definition code for java.lang.Object 
  extended by java.util.concurrent.locks.AbstractQueuedSynchronizer
All Implemented Interfaces:
Serializable sample code for java.io.Serializable definition code for java.io.Serializable

public abstract class AbstractQueuedSynchronizer
extends Object sample code for java.lang.Object definition code for java.lang.Object
implements Serializable sample code for java.io.Serializable definition code for java.io.Serializable

Provides a framework for implementing blocking locks and related synchronizers (semaphores, events, etc) that rely on first-in-first-out (FIFO) wait queues. This class is designed to be a useful basis for most kinds of synchronizers that rely on a single atomic int value to represent state. Subclasses must define the protected methods that change this state, and which define what that state means in terms of this object being acquired or released. Given these, the other methods in this class carry out all queuing and blocking mechanics. Subclasses can maintain other state fields, but only the atomically updated int value manipulated using methods getState() sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getState() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getState() , setState(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.setState(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.setState(int) and compareAndSetState(int, int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.compareAndSetState(int, int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.compareAndSetState(int, int) is tracked with respect to synchronization.

Subclasses should be defined as non-public internal helper classes that are used to implement the synchronization properties of their enclosing class. Class AbstractQueuedSynchronizer does not implement any synchronization interface. Instead it defines methods such as acquireInterruptibly(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireInterruptibly(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireInterruptibly(int) that can be invoked as appropriate by concrete locks and related synchronizers to implement their public methods.

This class supports either or both a default exclusive mode and a shared mode. When acquired in exclusive mode, attempted acquires by other threads cannot succeed. Shared mode acquires by multiple threads may (but need not) succeed. This class does not "understand" these differences except in the mechanical sense that when a shared mode acquire succeeds, the next waiting thread (if one exists) must also determine whether it can acquire as well. Threads waiting in the different modes share the same FIFO queue. Usually, implementation subclasses support only one of these modes, but both can come into play for example in a ReadWriteLock sample code for java.util.concurrent.locks.ReadWriteLock definition code for java.util.concurrent.locks.ReadWriteLock . Subclasses that support only exclusive or only shared modes need not define the methods supporting the unused mode.

This class defines a nested AbstractQueuedSynchronizer.ConditionObject sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject class that can be used as a Condition sample code for java.util.concurrent.locks.Condition definition code for java.util.concurrent.locks.Condition implementation by subclasses supporting exclusive mode for which method isHeldExclusively() sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.isHeldExclusively() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.isHeldExclusively() reports whether synchronization is exclusively held with respect to the current thread, method release(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.release(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.release(int) invoked with the current getState() sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getState() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getState() value fully releases this object, and acquire(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(int) , given this saved state value, eventually restores this object to its previous acquired state. No AbstractQueuedSynchronizer method otherwise creates such a condition, so if this constraint cannot be met, do not use it. The behavior of AbstractQueuedSynchronizer.ConditionObject sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject depends of course on the semantics of its synchronizer implementation.

This class provides inspection, instrumentation, and monitoring methods for the internal queue, as well as similar methods for condition objects. These can be exported as desired into classes using an AbstractQueuedSynchronizer for their synchronization mechanics.

Serialization of this class stores only the underlying atomic integer maintaining state, so deserialized objects have empty thread queues. Typical subclasses requiring serializability will define a readObject method that restores this to a known initial state upon deserialization.

Usage

To use this class as the basis of a synchronizer, redefine the following methods, as applicable, by inspecting and/or modifying the synchronization state using getState() sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getState() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getState() , setState(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.setState(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.setState(int) and/or compareAndSetState(int, int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.compareAndSetState(int, int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.compareAndSetState(int, int) :

Each of these methods by default throws UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException . Implementations of these methods must be internally thread-safe, and should in general be short and not block. Defining these methods is the only supported means of using this class. All other methods are declared final because they cannot be independently varied.

Even though this class is based on an internal FIFO queue, it does not automatically enforce FIFO acquisition policies. The core of exclusive synchronization takes the form:

 Acquire:
     while (!tryAcquire(arg)) {
        enqueue thread if it is not already queued;
        possibly block current thread;
     }

 Release:
     if (tryRelease(arg))
        unblock the first queued thread;
 
(Shared mode is similar but may involve cascading signals.)

Because checks in acquire are invoked before enqueuing, a newly acquiring thread may barge ahead of others that are blocked and queued. However, you can, if desired, define tryAcquire and/or tryAcquireShared to disable barging by internally invoking one or more of the inspection methods. In particular, a strict FIFO lock can define tryAcquire to immediately return false if getFirstQueuedThread() sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getFirstQueuedThread() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getFirstQueuedThread() does not return the current thread. A normally preferable non-strict fair version can immediately return false only if hasQueuedThreads() sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasQueuedThreads() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasQueuedThreads() returns true and getFirstQueuedThread is not the current thread; or equivalently, that getFirstQueuedThread is both non-null and not the current thread. Further variations are possible.

Throughput and scalability are generally highest for the default barging (also known as greedy, renouncement, and convoy-avoidance) strategy. While this is not guaranteed to be fair or starvation-free, earlier queued threads are allowed to recontend before later queued threads, and each recontention has an unbiased chance to succeed against incoming threads. Also, while acquires do not "spin" in the usual sense, they may perform multiple invocations of tryAcquire interspersed with other computations before blocking. This gives most of the benefits of spins when exclusive synchronization is only briefly held, without most of the liabilities when it isn't. If so desired, you can augment this by preceding calls to acquire methods with "fast-path" checks, possibly prechecking hasContended() sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasContended() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasContended() and/or hasQueuedThreads() sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasQueuedThreads() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasQueuedThreads() to only do so if the synchronizer is likely not to be contended.

This class provides an efficient and scalable basis for synchronization in part by specializing its range of use to synchronizers that can rely on int state, acquire, and release parameters, and an internal FIFO wait queue. When this does not suffice, you can build synchronizers from a lower level using atomic classes, your own custom Queue sample code for java.util.Queue definition code for java.util.Queue classes, and LockSupport sample code for java.util.concurrent.locks.LockSupport definition code for java.util.concurrent.locks.LockSupport blocking support.

Usage Examples

Here is a non-reentrant mutual exclusion lock class that uses the value zero to represent the unlocked state, and one to represent the locked state. It also supports conditions and exposes one of the instrumentation methods:

 class Mutex implements Lock, java.io.Serializable {

    // Our internal helper class
    private static class Sync extends AbstractQueuedSynchronizer {
      // Report whether in locked state
      protected boolean isHeldExclusively() { 
        return getState() == 1; 
      }

      // Acquire the lock if state is zero
      public boolean tryAcquire(int acquires) {
        assert acquires == 1; // Otherwise unused
        return compareAndSetState(0, 1);
      }

      // Release the lock by setting state to zero
      protected boolean tryRelease(int releases) {
        assert releases == 1; // Otherwise unused
        if (getState() == 0) throw new IllegalMonitorStateException();
        setState(0);
        return true;
      }
       
      // Provide a Condition
      Condition newCondition() { return new ConditionObject(); }

      // Deserialize properly
      private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException {
        s.defaultReadObject();
        setState(0); // reset to unlocked state
      }
    }

    // The sync object does all the hard work. We just forward to it.
    private final Sync sync = new Sync();

    public void lock()                { sync.acquire(1); }
    public boolean tryLock()          { return sync.tryAcquire(1); }
    public void unlock()              { sync.release(1); }
    public Condition newCondition()   { return sync.newCondition(); }
    public boolean isLocked()         { return sync.isHeldExclusively(); }
    public boolean hasQueuedThreads() { return sync.hasQueuedThreads(); }
    public void lockInterruptibly() throws InterruptedException { 
      sync.acquireInterruptibly(1);
    }
    public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException {
      return sync.tryAcquireNanos(1, unit.toNanos(timeout));
    }
 }
 

Here is a latch class that is like a CountDownLatch sample code for java.util.concurrent.CountDownLatch definition code for java.util.concurrent.CountDownLatch except that it only requires a single signal to fire. Because a latch is non-exclusive, it uses the shared acquire and release methods.

 class BooleanLatch {

    private static class Sync extends AbstractQueuedSynchronizer {
      boolean isSignalled() { return getState() != 0; }

      protected int tryAcquireShared(int ignore) {
        return isSignalled()? 1 : -1;
      }
        
      protected boolean tryReleaseShared(int ignore) {
        setState(1);
        return true;
      }
    }

    private final Sync sync = new Sync();
    public boolean isSignalled() { return sync.isSignalled(); }
    public void signal()         { sync.releaseShared(1); }
    public void await() throws InterruptedException {
      sync.acquireSharedInterruptibly(1);
    }
 }

 

Since:
1.5
See Also:
Serialized Form

Nested Class Summary
 class AbstractQueuedSynchronizer.ConditionObject sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject
          Condition implementation for a AbstractQueuedSynchronizer sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer serving as the basis of a Lock sample code for java.util.concurrent.locks.Lock definition code for java.util.concurrent.locks.Lock implementation.
 
Constructor Summary
protected AbstractQueuedSynchronizer sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.AbstractQueuedSynchronizer() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.AbstractQueuedSynchronizer() ()
          Creates a new AbstractQueuedSynchronizer instance with initial synchronization state of zero.
 
Method Summary
 void acquire sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(int) (int arg)
          Acquires in exclusive mode, ignoring interrupts.
 void acquireInterruptibly sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireInterruptibly(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireInterruptibly(int) (int arg)
          Acquires in exclusive mode, aborting if interrupted.
 void acquireShared sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireShared(int) (int arg)
          Acquires in shared mode, ignoring interrupts.
 void acquireSharedInterruptibly sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(int) (int arg)
          Acquires in shared mode, aborting if interrupted.
protected  boolean compareAndSetState sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.compareAndSetState(int, int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.compareAndSetState(int, int) (int expect, int update)
          Atomically sets synchronization state to the given updated value if the current state value equals the expected value.
 Collection sample code for java.util.Collection definition code for java.util.Collection <Thread sample code for java.lang.Thread definition code for java.lang.Thread > getExclusiveQueuedThreads sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getExclusiveQueuedThreads() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getExclusiveQueuedThreads() ()
          Returns a collection containing threads that may be waiting to acquire in exclusive mode.
 Thread sample code for java.lang.Thread definition code for java.lang.Thread getFirstQueuedThread sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getFirstQueuedThread() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getFirstQueuedThread() ()
          Returns the first (longest-waiting) thread in the queue, or null if no threads are currently queued.
 Collection sample code for java.util.Collection definition code for java.util.Collection <Thread sample code for java.lang.Thread definition code for java.lang.Thread > getQueuedThreads sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getQueuedThreads() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getQueuedThreads() ()
          Returns a collection containing threads that may be waiting to acquire.
 int getQueueLength sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getQueueLength() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getQueueLength() ()
          Returns an estimate of the number of threads waiting to acquire.
 Collection sample code for java.util.Collection definition code for java.util.Collection <Thread sample code for java.lang.Thread definition code for java.lang.Thread > getSharedQueuedThreads sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getSharedQueuedThreads() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getSharedQueuedThreads() ()
          Returns a collection containing threads that may be waiting to acquire in shared mode.
protected  int getState sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getState() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getState() ()
          Returns the current value of synchronization state.
 Collection sample code for java.util.Collection definition code for java.util.Collection <Thread sample code for java.lang.Thread definition code for java.lang.Thread > getWaitingThreads sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getWaitingThreads(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getWaitingThreads(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject) (AbstractQueuedSynchronizer.ConditionObject sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject  condition)
          Returns a collection containing those threads that may be waiting on the given condition associated with this synchronizer.
 int getWaitQueueLength sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getWaitQueueLength(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getWaitQueueLength(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject) (AbstractQueuedSynchronizer.ConditionObject sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject  condition)
          Returns an estimate of the number of threads waiting on the given condition associated with this synchronizer.
 boolean hasContended sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasContended() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasContended() ()
          Queries whether any threads have ever contended to acquire this synchronizer; that is if an acquire method has ever blocked.
 boolean hasQueuedThreads sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasQueuedThreads() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasQueuedThreads() ()
          Queries whether any threads are waiting to acquire.
 boolean hasWaiters sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasWaiters(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasWaiters(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject) (AbstractQueuedSynchronizer.ConditionObject sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject  condition)
          Queries whether any threads are waiting on the given condition associated with this synchronizer.
protected  boolean isHeldExclusively sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.isHeldExclusively() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.isHeldExclusively() ()
          Returns true if synchronization is held exclusively with respect to the current (calling) thread.
 boolean isQueued sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.isQueued(java.lang.Thread) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.isQueued(java.lang.Thread) (Thread sample code for java.lang.Thread definition code for java.lang.Thread  thread)
          Returns true if the given thread is currently queued.
 boolean owns sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.owns(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.owns(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject) (AbstractQueuedSynchronizer.ConditionObject sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject  condition)
          Queries whether the given ConditionObject uses this synchronizer as its lock.
 boolean release sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.release(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.release(int) (int arg)
          Releases in exclusive mode.
 boolean releaseShared sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.releaseShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.releaseShared(int) (int arg)
          Releases in shared mode.
protected  void setState sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.setState(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.setState(int) (int newState)
          Sets the value of synchronization state.
 String sample code for java.lang.String definition code for java.lang.String toString sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.toString() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.toString() ()
          Returns a string identifying this synchronizer, as well as its state.
protected  boolean tryAcquire sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) (int arg)
          Attempts to acquire in exclusive mode.
 boolean tryAcquireNanos sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireNanos(int, long) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireNanos(int, long) (int arg, long nanosTimeout)
          Attempts to acquire in exclusive mode, aborting if interrupted, and failing if the given timeout elapses.
protected  int tryAcquireShared sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) (int arg)
          Attempts to acquire in shared mode.
 boolean tryAcquireSharedNanos sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireSharedNanos(int, long) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireSharedNanos(int, long) (int arg, long nanosTimeout)
          Attempts to acquire in shared mode, aborting if interrupted, and failing if the given timeout elapses.
protected  boolean tryRelease sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryRelease(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryRelease(int) (int arg)
          Attempts to set the state to reflect a release in exclusive mode.
protected  boolean tryReleaseShared sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryReleaseShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryReleaseShared(int) (int arg)
          Attempts to set the state to reflect a release in shared mode.
 
Methods inherited from class java.lang.Object sample code for java.lang.Object definition code for java.lang.Object
clone sample code for java.lang.Object.clone() definition code for java.lang.Object.clone() , equals sample code for java.lang.Object.equals(java.lang.Object) definition code for java.lang.Object.equals(java.lang.Object) , finalize sample code for java.lang.Object.finalize() definition code for java.lang.Object.finalize() , getClass sample code for java.lang.Object.getClass() definition code for java.lang.Object.getClass() , hashCode sample code for java.lang.Object.hashCode() definition code for java.lang.Object.hashCode() , notify sample code for java.lang.Object.notify() definition code for java.lang.Object.notify() , notifyAll sample code for java.lang.Object.notifyAll() definition code for java.lang.Object.notifyAll() , wait sample code for java.lang.Object.wait() definition code for java.lang.Object.wait() , wait sample code for java.lang.Object.wait(long) definition code for java.lang.Object.wait(long) , wait sample code for java.lang.Object.wait(long, int) definition code for java.lang.Object.wait(long, int)
 

Constructor Detail

AbstractQueuedSynchronizer sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer()

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

Method Detail

getState sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getState() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getState()

protected final int getState()
Returns the current value of synchronization state. This operation has memory semantics of a volatile read.

Returns:
current state value

setState sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.setState(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.setState(int)

protected final void setState(int newState)
Sets the value of synchronization state. This operation has memory semantics of a volatile write.

Parameters:
newState - the new state value

compareAndSetState sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.compareAndSetState(int, int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.compareAndSetState(int, int)

protected final boolean compareAndSetState(int expect,
                                           int 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 sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int)

protected boolean tryAcquire(int 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() sample code for java.util.concurrent.locks.Lock.tryLock() definition code for java.util.concurrent.locks.Lock.tryLock() .

The default implementation throws UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.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 sample code for java.lang.IllegalMonitorStateException definition code for java.lang.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 sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if exclusive mode is not supported

tryRelease sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryRelease(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryRelease(int)

protected boolean tryRelease(int 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 sample code for java.lang.UnsupportedOperationException definition code for java.lang.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 sample code for java.lang.IllegalMonitorStateException definition code for java.lang.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 sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if exclusive mode is not supported

tryAcquireShared sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int)

protected int tryAcquireShared(int 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 sample code for java.lang.UnsupportedOperationException definition code for java.lang.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 on exclusive success, and a positive value if non-exclusively successful, 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 sample code for java.lang.IllegalMonitorStateException definition code for java.lang.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 sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if shared mode is not supported

tryReleaseShared sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryReleaseShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryReleaseShared(int)

protected boolean tryReleaseShared(int 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 sample code for java.lang.UnsupportedOperationException definition code for java.lang.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 sample code for java.lang.IllegalMonitorStateException definition code for java.lang.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 sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if shared mode is not supported

isHeldExclusively sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.isHeldExclusively() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.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 AbstractQueuedSynchronizer.ConditionObject sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject method. (Waiting methods instead invoke release(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.release(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.release(int) .)

The default implementation throws UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException . This method is invoked internally only within AbstractQueuedSynchronizer.ConditionObject sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject methods, so need not be defined if conditions are not used.

Returns:
true if synchronization is held exclusively; else false
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if conditions are not supported

acquire sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(int)

public final void acquire(int arg)
Acquires in exclusive mode, ignoring interrupts. Implemented by invoking at least once tryAcquire(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) , returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquire(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) until success. This method can be used to implement method Lock.lock() sample code for java.util.concurrent.locks.Lock.lock() definition code for java.util.concurrent.locks.Lock.lock()

Parameters:
arg - the acquire argument. This value is conveyed to tryAcquire(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) but is otherwise uninterpreted and can represent anything you like.

acquireInterruptibly sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireInterruptibly(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireInterruptibly(int)

public final void acquireInterruptibly(int arg)
                                throws InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException 
Acquires in exclusive mode, aborting if interrupted. Implemented by first checking interrupt status, then invoking at least once tryAcquire(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) , returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquire(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) until success or the thread is interrupted. This method can be used to implement method Lock.lockInterruptibly() sample code for java.util.concurrent.locks.Lock.lockInterruptibly() definition code for java.util.concurrent.locks.Lock.lockInterruptibly()

Parameters:
arg - the acquire argument. This value is conveyed to tryAcquire(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) but is otherwise uninterpreted and can represent anything you like.
Throws:
InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException - if the current thread is interrupted

tryAcquireNanos sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireNanos(int, long) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireNanos(int, long)

public final boolean tryAcquireNanos(int arg,
                                     long nanosTimeout)
                              throws InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.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(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) , returning on success. Otherwise, the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquire(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) until success or the thread is interrupted or the timeout elapses. This method can be used to implement method Lock.tryLock(long, TimeUnit) sample code for java.util.concurrent.locks.Lock.tryLock(long, java.util.concurrent.TimeUnit) definition code for java.util.concurrent.locks.Lock.tryLock(long, java.util.concurrent.TimeUnit) .

Parameters:
arg - the acquire argument. This value is conveyed to tryAcquire(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquire(int) 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 sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException - if the current thread is interrupted

release sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.release(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.release(int)

public final boolean release(int arg)
Releases in exclusive mode. Implemented by unblocking one or more threads if tryRelease(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryRelease(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryRelease(int) returns true. This method can be used to implement method Lock.unlock() sample code for java.util.concurrent.locks.Lock.unlock() definition code for java.util.concurrent.locks.Lock.unlock()

Parameters:
arg - the release argument. This value is conveyed to tryRelease(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryRelease(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryRelease(int) but is otherwise uninterpreted and can represent anything you like.
Returns:
the value returned from tryRelease(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryRelease(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryRelease(int)

acquireShared sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireShared(int)

public final void acquireShared(int arg)
Acquires in shared mode, ignoring interrupts. Implemented by first invoking at least once tryAcquireShared(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) , returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquireShared(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) until success.

Parameters:
arg - the acquire argument. This value is conveyed to tryAcquireShared(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) but is otherwise uninterpreted and can represent anything you like.

acquireSharedInterruptibly sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(int)

public final void acquireSharedInterruptibly(int arg)
                                      throws InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException 
Acquires in shared mode, aborting if interrupted. Implemented by first checking interrupt status, then invoking at least once tryAcquireShared(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) , returning on success. Otherwise the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquireShared(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) until success or the thread is interrupted.

Parameters:
arg - the acquire argument. This value is conveyed to tryAcquireShared(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) but is otherwise uninterpreted and can represent anything you like.
Throws:
InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException - if the current thread is interrupted

tryAcquireSharedNanos sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireSharedNanos(int, long) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireSharedNanos(int, long)

public final boolean tryAcquireSharedNanos(int arg,
                                           long nanosTimeout)
                                    throws InterruptedException sample code for java.lang.InterruptedException definition code for java.lang.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(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) , returning on success. Otherwise, the thread is queued, possibly repeatedly blocking and unblocking, invoking tryAcquireShared(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) until success or the thread is interrupted or the timeout elapses.

Parameters:
arg - the acquire argument. This value is conveyed to tryAcquireShared(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireShared(int) 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 sample code for java.lang.InterruptedException definition code for java.lang.InterruptedException - if the current thread is interrupted

releaseShared sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.releaseShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.releaseShared(int)

public final boolean releaseShared(int arg)
Releases in shared mode. Implemented by unblocking one or more threads if tryReleaseShared(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryReleaseShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryReleaseShared(int) returns true.

Parameters:
arg - the release argument. This value is conveyed to tryReleaseShared(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryReleaseShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryReleaseShared(int) but is otherwise uninterpreted and can represent anything you like.
Returns:
the value returned from tryReleaseShared(int) sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryReleaseShared(int) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.tryReleaseShared(int)

hasQueuedThreads sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasQueuedThreads() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.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 the lock.

hasContended sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasContended() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.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 sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getFirstQueuedThread() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getFirstQueuedThread()

public final Thread sample code for java.lang.Thread definition code for java.lang.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 sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.isQueued(java.lang.Thread) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.isQueued(java.lang.Thread)

public final boolean isQueued(Thread sample code for java.lang.Thread definition code for java.lang.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 in on the queue
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if thread null

getQueueLength sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getQueueLength() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.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 for this lock

getQueuedThreads sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getQueuedThreads() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getQueuedThreads()

public final Collection sample code for java.util.Collection definition code for java.util.Collection <Thread sample code for java.lang.Thread definition code for java.lang.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 sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getExclusiveQueuedThreads() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getExclusiveQueuedThreads()

public final Collection sample code for java.util.Collection definition code for java.util.Collection <Thread sample code for java.lang.Thread definition code for java.lang.Thread > getExclusiveQueuedThreads()
Returns a collection containing threads that may be waiting to acquire in exclusive mode. This has the same properties as getQueuedThreads() sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getQueuedThreads() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getQueuedThreads() except that it only returns those threads waiting due to an exclusive acquire.

Returns:
the collection of threads

getSharedQueuedThreads sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getSharedQueuedThreads() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getSharedQueuedThreads()

public final Collection sample code for java.util.Collection definition code for java.util.Collection <Thread sample code for java.lang.Thread definition code for java.lang.Thread > getSharedQueuedThreads()
Returns a collection containing threads that may be waiting to acquire in shared mode. This has the same properties as getQueuedThreads() sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getQueuedThreads() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getQueuedThreads() except that it only returns those threads waiting due to a shared acquire.

Returns:
the collection of threads

toString sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.toString() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.toString()

public String sample code for java.lang.String definition code for java.lang.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() sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getState() definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getState() , and either "nonempty" or "empty" depending on whether the queue is empty.

Overrides:
toString sample code for java.lang.Object.toString() definition code for java.lang.Object.toString() in class Object sample code for java.lang.Object definition code for java.lang.Object
Returns:
a string identifying this synchronizer, as well as its state.

owns sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.owns(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.owns(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject)

public final boolean owns(AbstractQueuedSynchronizer.ConditionObject sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject  condition)
Queries whether the given ConditionObject uses this synchronizer as its lock.

Parameters:
condition - the condition
Returns:
true if owned
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if condition null

hasWaiters sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasWaiters(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.hasWaiters(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject)

public final boolean hasWaiters(AbstractQueuedSynchronizer.ConditionObject sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.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 sample code for java.lang.IllegalMonitorStateException definition code for java.lang.IllegalMonitorStateException - if exclusive synchronization is not held
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if the given condition is not associated with this synchronizer
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if condition null

getWaitQueueLength sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getWaitQueueLength(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getWaitQueueLength(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject)

public final int getWaitQueueLength(AbstractQueuedSynchronizer.ConditionObject sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.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 sample code for java.lang.IllegalMonitorStateException definition code for java.lang.IllegalMonitorStateException - if exclusive synchronization is not held
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if the given condition is not associated with this synchronizer
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if condition null

getWaitingThreads sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getWaitingThreads(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject) definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.getWaitingThreads(java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject)

public final Collection sample code for java.util.Collection definition code for java.util.Collection <Thread sample code for java.lang.Thread definition code for java.lang.Thread > getWaitingThreads(AbstractQueuedSynchronizer.ConditionObject sample code for java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject definition code for java.util.concurrent.locks.AbstractQueuedSynchronizer.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 sample code for java.lang.IllegalMonitorStateException definition code for java.lang.IllegalMonitorStateException - if exclusive synchronization is not held
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if the given condition is not associated with this synchronizer
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if condition null