Blocking Queue : Queue « Collections Data Structure « Java






Blocking Queue

    
/**
 * The utillib library.
 * More information is available at http://www.jinchess.com/.
 * Copyright (C) 2002 Alexander Maryanovsky.
 * All rights reserved.
 *
 * The utillib library is free software; you can redistribute
 * it and/or modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * The utillib library is distributed in the hope that it will
 * be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
 * General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with utillib library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */


import java.util.Enumeration;
import java.util.Vector;

/**
 * <P>A blocking queue, one that always "contains" elements.
 * If it is in fact empty, the pop() and peek() method will block until an
 * item is pushed.
 * <P><B>NOTE:</B> This class is thread safe.
 *
 * @author Alexander Maryanovsky.
 */

public class BlockingQueue implements Cloneable{


  /**
   * The underlying Vector this BlockingQueue is using.
   */

  private final Vector queue;


  /**
   * The lock we use to synchronize pushing.
   */

  private final Object pushLock = new String("BlockingQueue pushLock");


  /**
   * The lock we use to synchronize popping.
   */

  private final Object popLock = new String("BlockingQueue popLock");




  /**
   * Creates a new, empty BlockingQueue.
   */

  public BlockingQueue(){
    queue = new Vector();
  }





  /**
   * Pushes an element into the queue.
   */

  public void push(Object object){
    synchronized(pushLock){
      queue.addElement(object);
      synchronized(this){
        notify();
      }
    }
  }



  /**
   * Pops an element from the queue. If the queue is empty, this method blocks
   * until another thread pushes an element into the queue.
   *
   * @throws InterruptedException if the invoking thread was interrupted
   * while waiting for an element to be pushed into the queue.
   */

  public Object pop() throws InterruptedException{
    return pop(0);
  }



  /**
   * Pops an element from the queue. Unlike the pop() method, this method does not block
   * for longer than the given amount of milliseconds. When the given amount of milliseconds
   * have passed, this method will throw an InterruptedException.
   */

  public Object pop(long timeout) throws InterruptedException{
    synchronized(popLock){
      synchronized(this){
        if (queue.isEmpty()){
          wait(timeout);
          if (queue.isEmpty())
            throw new InterruptedException("Timed out");
        }
      }
      Object val = queue.firstElement();
      queue.removeElementAt(0);
      return val;
    }
  }



  /**
   * Returns the element on top of the queue without popping it. If the queue
   * is empty, this method blocks until another thread pushes an element into
   * the queue.
   *
   * @throws InterruptedException if the invoking thread was interrupted while
   * waiting for an element to be pushed into the queue.
   */

  public Object peek() throws InterruptedException{
    return peek(0);
  }




  /**
   * Returns the element on top of the queue without popping it.
   * Unlike the peek() method, this method does not block
   * for longer than the given amount of milliseconds. When the given amount of milliseconds
   * have passed, this method will throw an InterruptedException.
   */

  public Object peek(long timeout) throws InterruptedException{
    synchronized(popLock){
      synchronized(this){
        if (queue.isEmpty()){
          wait(timeout);
          if (queue.isEmpty())
            throw new InterruptedException("Timed out");
        }
      }
      return queue.firstElement();
    }
  }






  /**
   * Returns true if the queue is empty (this returns the actual state of the
   * queue, meaning it may return true even though ideologically, a BlockingQueue
   * is never empty).
   */

  public boolean isEmpty(){
    return queue.isEmpty();
  }



  /**
   * Returns true if the given element is in the queue.
   */

  public boolean contains(Object element){
    return queue.contains(element);
  }



  /**
   * Returns the size of the queue.
   */

  public int size(){
    return queue.size();
  }



  /**
   * Returns an Enumeration of the elements in this queue. The order of the
   * elements is the same as if they were popped from the queue one by one (the
   * first element is the first element that would have been popped). <br>
   * <B>IMPORTANT:</B> Modifying the queue breaks the returned Enumeration.
   */

  public Enumeration getElements(){
    return queue.elements();
  }



  /**
   * Removes all elements from this queue.
   */

  public void removeAllElements(){
    queue.removeAllElements();
  }



  /**
   * Removes all elements from this queue.
   */

  public void clear(){
    queue.removeAllElements();
  }



  /**
   * Returns a shallow copy of this BlockingQueue.
   */

  public synchronized Object clone(){
    BlockingQueue copy = new BlockingQueue();
    Enumeration elems = getElements();
    while (elems.hasMoreElements()){
      Object item = elems.nextElement();
      copy.push(item);
    }
    return copy;
  }



}

   
    
    
    
  








Related examples in the same category

1.Priority queuePriority queue
2.Queue data structureQueue data structure
3.Convert a Queue to a List
4.Create a queue using LinkedList class
5.Simple Queue (FIFO) based on LinkedList
6.The Generic Queue Class
7.Circular Queue
8.Circular Queue extends AbstractList
9.How to extend the collections framework
10.An unbounded {@link TransferQueue} based on linked nodes.
11.This class implements the data structures necessary for an ArrayQueue
12.A circular queue from mina
13.An unbounded TransferQueue based on linked nodes.
14.Rotating queue of fixed size.
15.Allows threads to communicate asynchronously by putting messages into and reading messages out of a synchronized queue.