BlockingQueueE

BlockingQueue<E>

java.util.concurrent

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Java 5.0

collection

This interface extends the java.util.Queue interface of the Java Collections Framework and adds blocking put( ) and take( ) methods . Blocking queues are useful in many concurrent algorithms in which a producer thread puts objects onto a queue and a consumer thread removes them for some kind of processing. The producer thread must block if a bounded queue fills up, and the consumer thread must block if no objects are available on the queue.

In addition to put( ) and take( ) methods that block indefinitely, BlockingQueue also defines timed versions of the Queue methods offer( ) and poll( ) that wait up to the specified time. The timeout is specified as both a long and a TimeUnit constant.

drainTo( ) removes all available elements from a BlockingQueue , adds them to the specified collection, and returns the number of elements removed from the queue. drainTo( ) does not block. A variant on this method puts an upper bound on the number of elements removed from the queue.

remainingCapacity( ) returns the number of elements that can be added to the queue before it becomes full or returns Integer.MAX_VALUE if the BlockingQueue is not a bounded queue. For bounded queues, this method provides a hint as to whether a call to put( ) will block.

BlockingQueue implementations are not allowed to accept null elements. The BlockingQueue interface refines the Collection.add( ) and Queue.offer( ) contracts to indicate that these methods throw NullPointerException if passed a null value.

Figure 16-72. java.util.concurrent.BlockingQueue<E>

 public interface  BlockingQueue<E>  extends java.util.Queue<E> {  // Public Instance Methods  boolean  add  (E  o  );        int  drainTo  (java.util.Collection<? super E>  c  );        int  drainTo  (java.util.Collection<? super E>  c  , int  maxElements  );        boolean  offer  (E  o  );        boolean  offer  (E  o  , long  timeout  , TimeUnit  unit  ) throws InterruptedException;        E  poll  (long  timeout  , TimeUnit  unit  ) throws InterruptedException;        void  put  (E  o  ) throws InterruptedException;        int  remainingCapacity  ( );        E  take  ( ) throws InterruptedException;   } 

Implementations

ArrayBlockingQueue , DelayQueue , LinkedBlockingQueue , PriorityBlockingQueue , SynchronousQueue

Passed To

ExecutorCompletionService.ExecutorCompletionService( ) , ThreadPoolExecutor.ThreadPoolExecutor( )

Returned By

ScheduledThreadPoolExecutor.getQueue( ) , ThreadPoolExecutor.getQueue( )