/interpreter/tags/at2dist041108/src/edu/vub/at/actors/eventloops/EventQueue.java

  1/**
  2 * AmbientTalk/2 Project
  3 * EventQueue.java created on 21-dec-2006 at 11:30:59
  4 * (c) Programming Technology Lab, 2006 - 2007
  5 * Authors: Tom Van Cutsem & Stijn Mostinckx
  6 * 
  7 * Permission is hereby granted, free of charge, to any person
  8 * obtaining a copy of this software and associated documentation
  9 * files (the "Software"), to deal in the Software without
 10 * restriction, including without limitation the rights to use,
 11 * copy, modify, merge, publish, distribute, sublicense, and/or
 12 * sell copies of the Software, and to permit persons to whom the
 13 * Software is furnished to do so, subject to the following
 14 * conditions:
 15 *
 16 * The above copyright notice and this permission notice shall be
 17 * included in all copies or substantial portions of the Software.
 18 *
 19 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 20 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 21 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 22 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 23 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 24 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 25 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 26 * OTHER DEALINGS IN THE SOFTWARE.
 27 */
 28package edu.vub.at.actors.eventloops;
 29
 30import java.util.Vector;
 31
 32/**
 33 * A simple synchronized blocking FIFO queue implementation.
 34 * The buffer will grow dynamically to accomodate more events when necessary.
 35 *
 36 * @author tvcutsem
 37 */
 38public final class EventQueue {
 39
 40	private static final int _DEFAULT_QUEUE_SIZE_ = 10;
 41	
 42	private final Vector elements_;
 43	
 44	/** Constructor which creates an empty EventQueue */
 45	public EventQueue() {
 46		elements_ = new Vector(_DEFAULT_QUEUE_SIZE_);
 47	}
 48	
 49	/**
 50	 * Enqueue an event in the buffer. This method wakes up any
 51	 * waiting consumer threads.
 52	 */
 53	public void enqueue(Event event) {
 54		synchronized(this) {
 55			elements_.add(event);
 56			notifyAll();
 57		}
 58	}
 59	
 60	/**
 61	 * Enqueue an event as the first to be executed in the buffer. 
 62	 * This method wakes up any waiting consumer threads.
 63	 */
 64	public void enqueueFirst(Event event) {
 65		synchronized(this) {
 66			elements_.add(0, event);
 67			notifyAll();
 68		}
 69	}
 70	
 71	/**
 72	 * Dequeue an event from the buffer. This method will block when the
 73	 * buffer is empty!
 74	 * 
 75	 * @return the dequeued event.
 76	 * @throws InterruptedException if the thread is interrupted while waiting on an empty buffer.
 77	 */
 78	public Event dequeue() throws InterruptedException {
 79		synchronized(this) {
 80			while(elements_.isEmpty()) {
 81				wait();
 82			}
 83			return (Event) elements_.remove(0);
 84		}
 85	}
 86	
 87	/**
 88	 * Clears the content of the buffer and returns the old contents.
 89	 * @return the buffer's content at the time it was flushed
 90	 */
 91	public Vector flush() {
 92		synchronized(this) {
 93			Vector copy = (Vector) elements_.clone();
 94			elements_.clear();
 95			return copy;
 96		}
 97	}
 98	
 99	/**
100	 * Allows for restoring the buffer's old contents by putting
101	 * the elements in contents in front of the buffer.
102	 */
103	public void merge(Vector contents) {
104		synchronized(this) {
105			elements_.addAll(0, contents);
106		}
107	}
108	
109	/**
110	 * Tests whether the event queue is empty. This test is provided to
111	 * allow clients of the queue to perform synchronization on an external
112	 * resource if necessary.
113	 */
114	public boolean isEmpty() {
115		synchronized (this) {
116			return elements_.isEmpty();
117		}
118	}
119	
120}