SwingWorker.java

/***
 * Copyright (c) 2008, Endless Loop Software, Inc.
 * 
 * This file is part of EgoNet.
 * 
 * EgoNet is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 * 
 * EgoNet 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 General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.egonet.util;

import javax.swing.SwingUtilities;

public abstract class SwingWorker
{
	private Object value;  // see getValue(), setValue()
	private Thread thread;

	public final static Integer INDETERMINATE = new Integer(-1);

	/**
	 * Class to maintain reference to current worker thread
	 * under separate synchronization control.
	 */
	private static class ThreadVar
	{
		private Thread thread;
		ThreadVar(Thread t) { thread = t; }
		synchronized Thread get() { return thread; }
		synchronized void clear() { thread = null; }
		public String toString() { return thread == null ? "null" : thread.toString(); }
	}

	private ThreadVar threadVar;

	/**
	 * Get the value produced by the worker thread, or null if it
	 * hasn't been constructed yet.
	 * @return value set by worker thread
	 */
	protected synchronized Object getValue()
	{
		return value;
	}

	/**
	 * Set the value produced by worker thread
	 * @param x object to set as value
	 */
	private synchronized void setValue(Object x)
	{
		value = x;
	}

	/**
	 * Compute the value to be returned by the <code>get</code> method.
	 * @return Object returned from construct method of swingworker
	 */
	public abstract Object construct();

	/**
	 * Called on the event dispatching thread (not on the worker thread)
	 * after the <code>construct</code> method has returned.
	 */
	public void finished() {
	}

	/**
	 * A new method that interrupts the worker thread.  Call this method
	 * to force the worker to stop what it's doing.
	 */
	public void interrupt()
	{
		Thread t = threadVar.get();

		if (t != null)
		{
			t.interrupt();
		}

		threadVar.clear();
	}

	/**
	 * Return the value created by the <code>construct</code> method.
	 * Returns null if either the constructing thread or the current
	 * thread was interrupted before a value was produced.
	 *
	 * @return the value created by the <code>construct</code> method
	 */
	public Object get()
	{
		while (true)
		{
			Thread t = threadVar.get();
			if (t == null)
			{
				return getValue();
			}

			try
			{
				t.join();
			}
			catch (InterruptedException e)
			{
				Thread.currentThread().interrupt(); // propagate
				return null;
			}
		}
	}


	/**
	 * Start a thread that will call the <code>construct</code> method
	 * and then exit.
	 */
	public SwingWorker()
	{
		final Runnable doFinished = new Runnable()
		{
			public void run() { finished(); }
		};

		Runnable doConstruct = new Runnable()
		{
			public void run()
			{
				try
				{
					setValue(construct());
				}
				catch(Throwable cause) {
					throw new RuntimeException(cause);
				}
				finally
				{
					threadVar.clear();
				}

				SwingUtilities.invokeLater(doFinished);
			}
		};

		Thread t = new Thread(doConstruct);
		threadVar = new ThreadVar(t);
	}

	/**
	 * Start the worker thread.
	 */
	public void start()
	{
		Thread t = threadVar.get();
		if (t != null)
		{
			t.start();
		}
	}
	
	public String toString() { return thread == null ? "null" : thread.toString(); }	
}