/*
 *
 * Copyright (c) 1997-1999 Scott Oaks and Henry Wong. All Rights Reserved.
 *
 * Permission to use, copy, modify, and distribute this software
 * and its documentation for NON-COMMERCIAL purposes and
 * without fee is hereby granted.
 *
 * This sample source code is provided for example only,
 * on an unsupported, as-is basis. 
 *
 * AUTHOR MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
 * THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
 * TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE, OR NON-INFRINGEMENT. AUTHOR SHALL NOT BE LIABLE FOR
 * ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
 * DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
 *
 * THIS SOFTWARE IS NOT DESIGNED OR INTENDED FOR USE OR RESALE AS ON-LINE
 * CONTROL EQUIPMENT IN HAZARDOUS ENVIRONMENTS REQUIRING FAIL-SAFE
 * PERFORMANCE, SUCH AS IN THE OPERATION OF NUCLEAR FACILITIES, AIRCRAFT
 * NAVIGATION OR COMMUNICATION SYSTEMS, AIR TRAFFIC CONTROL, DIRECT LIFE
 * SUPPORT MACHINES, OR WEAPONS SYSTEMS, IN WHICH THE FAILURE OF THE
 * SOFTWARE COULD LEAD DIRECTLY TO DEATH, PERSONAL INJURY, OR SEVERE
 * PHYSICAL OR ENVIRONMENTAL DAMAGE ("HIGH RISK ACTIVITIES").  AUTHOR
 * SPECIFICALLY DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY OF FITNESS FOR
 * HIGH RISK ACTIVITIES.
 */


import java.util.Vector;

public class QueuedBusyFlag extends BusyFlag {
	protected Vector waiters;

	public QueuedBusyFlag() {
		waiters = new Vector();
	}

	public synchronized void getBusyFlag() {
		Thread me = Thread.currentThread();
		if (me == busyflag) {
			busycount++;
			return;
		}
		waiters.addElement(me);
		while ((Thread) waiters.elementAt(0) != me) {
			try {
				wait();
			} catch (Exception e) {}
		}
		busyflag = me;
		busycount = 0;
	}

	public synchronized void freeBusyflag() {
		if (Thread.currentThread() != busyflag)
			throw new IllegalArgumentException("QueuedBusyflag not held");
		if (busycount == 0) {
			waiters.removeElementAt(0);
			notifyAll();
			busyflag = null;
		}
		else busycount--;
	}

	public synchronized boolean tryGetBusyflag() {
		if (waiters.size() != 0 && busyflag != Thread.currentThread())
			return false;
		getBusyFlag();
		return true;
	}
}