| Semaphore | java.util.concurrent |
This class
implements semaphores , a classic thread
synchronization primitive that can be used to implement mutual
exclusion and wait/notify-style thread synchronization. A
Semaphore maintains some fixed number (specified
when the Semaphore( ) constructor is called) of
permits. The acquire( )
method blocks until a permit is available, then decrements the number
of available permits and returns. The release( )
method does the reverse: it increments the number of permits,
possibly unblocking a thread waiting in acquire(
).If you pass true as the second argument to the
Semaphore( ) constructor, the semaphore treats
waiting threads fairly by placing them on a FIFO queue in the order
they called acquire( ) and granting permits to the
threads in this order. This prevents thread starvation.
Figure 16-92. java.util.concurrent.Semaphore
 public class Semaphore implements Serializable {
// Public Constructors
public Semaphore (int permits );
public Semaphore (int permits , boolean fair );
// Public Instance Methods
public void acquire ( ) throws InterruptedException;
public void acquire (int permits ) throws InterruptedException;
public void acquireUninterruptibly ( );
public void acquireUninterruptibly (int permits );
public int availablePermits ( );
public int drainPermits ( );
public final int getQueueLength ( );
public final boolean hasQueuedThreads ( );
public boolean isFair ( );
public void release ( );
public void release (int permits );
public boolean tryAcquire ( );
public boolean tryAcquire (int permits );
public boolean tryAcquire (long timeout , TimeUnit unit )
throws InterruptedException;
public boolean tryAcquire (int permits , long timeout , TimeUnit unit )
throws InterruptedException;
// Public Methods Overriding Object
public String toString ( );
// Protected Instance Methods
protected java.util.Collection<Thread> getQueuedThreads ( );
protected void reducePermits (int reduction );
}
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