SimpleFIFOQueue.java

/****************************************************************************
 * Copyright (c) 2007 Composent, Inc. and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Composent, Inc. - initial API and implementation
 *****************************************************************************/

package org.eclipse.ecf.core.sharedobject.util;

import java.util.LinkedList;
import java.util.List;

public class SimpleFIFOQueue implements ISimpleFIFOQueue {
	private final List list;

	private volatile boolean stopped;

	public SimpleFIFOQueue() {
		list = new LinkedList();
		stopped = false;
	}

	@SuppressWarnings("unchecked")
	public synchronized boolean enqueue(final Object obj) {
		if (isStopped() || obj == null) {
			return false;
		}
		// Add item to the list
		list.add(obj);
		// Notify waiting thread. Dequeue should only be read by one thread, so
		// only need
		// notify() rather than notifyAll().
		notify();
		return true;
	}

	public synchronized Object dequeue() {
		final Object val = peekQueue();
		if (val != null) {
			removeHead();
		}
		return val;
	}

	public synchronized Object peekQueue() {
		while (isEmpty()) {
			if (stopped)
				return null;
			try {
				wait();
			} catch (final Exception e) {
				return null;
			}
		}
		return list.get(0);
	}

	public synchronized Object peekQueue(final long waitMS) {
		if (waitMS == 0)
			return peekQueue();
		if (stopped) {
			return null;
		}
		try {
			wait(waitMS);
		} catch (final Exception e) {
			return null;
		}
		if (isEmpty())
			return null;
		return list.get(0);
	}

	public synchronized Object removeHead() {
		if (list.isEmpty())
			return null;
		return list.remove(0);
	}

	public synchronized boolean isEmpty() {
		return list.isEmpty();
	}

	public synchronized void stop() {
		stopped = true;
	}

	public boolean isStopped() {
		return stopped;
	}

	public synchronized int size() {
		return list.size();
	}

	public synchronized Object[] flush() {
		final Object[] out = list.toArray();
		list.clear();
		close();
		return out;
	}

	public synchronized void close() {
		stop();
		notifyAll();
	}

	public String toString() {
		final StringBuffer sb = new StringBuffer("SimpleFIFOQueue["); //$NON-NLS-1$
		sb.append(list).append("]"); //$NON-NLS-1$
		return sb.toString();
	}
}