/*==========================================================================*\
| $Id: GraderQueue.java,v 1.2 2010/09/27 04:21:37 stedwar2 Exp $
|*-------------------------------------------------------------------------*|
| Copyright (C) 2006-2008 Virginia Tech
|
| This file is part of Web-CAT.
|
| Web-CAT is free software; you can redistribute it and/or modify
| it under the terms of the GNU Affero General Public License as published
| by the Free Software Foundation; either version 3 of the License, or
| (at your option) any later version.
|
| Web-CAT 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 General Public License for more details.
|
| You should have received a copy of the GNU Affero General Public License
| along with Web-CAT; if not, see <http://www.gnu.org/licenses/>.
\*==========================================================================*/
package org.webcat.grader;
import java.util.*;
import org.apache.log4j.Logger;
// -------------------------------------------------------------------------
/**
* This is the synchronous queue class for grader jobs. Why isn't a
* java.util class being used here instead?
*
* @author Amit Kulkarni
* @author Last changed by $Author: stedwar2 $
* @version $Revision: 1.2 $, $Date: 2010/09/27 04:21:37 $
*/
public class GraderQueue
{
//~ Constructors ..........................................................
// ----------------------------------------------------------
/**
* Default constructor
*/
public GraderQueue()
{
queue = new Vector<Object>();
}
//~ Methods ...............................................................
// ----------------------------------------------------------
/**
* suspends all processors till there is a job to process then wakes up a
* processor and gets a job
*
* @return the job
*/
public synchronized Object getJobToken()
{
try
{
while (queue.size() == 0)
{
wait();
}
// Here, after being woken up by notify(), we are guaranteed
// that the queue size is not zero and the current thread
// owns the monitor for this queue object
return dequeue();
}
catch (InterruptedException e)
{
log.error("GraderQueue client was interrupted while " +
"waiting for a job.");
return null;
}
}
// ----------------------------------------------------------
/**
* Puts a job in the queue.
*
* @param o the job to enqueue
*/
public synchronized void enqueue(Object o)
{
queue.add(o);
notify();
}
// ----------------------------------------------------------
/**
* Dequeues a job from the queue.
*
* @return a dequeued job
*/
private synchronized Object dequeue()
{
Object o = queue.elementAt(0);
queue.removeElementAt(0);
return o;
}
//~ Instance/static variables .............................................
/** The queue is maintained as a vector. */
Vector<Object> queue;
static Logger log = Logger.getLogger(GraderQueue.class);
}