/*
  File: SwingWorker.java

  Copyright (c) 2006, The Cytoscape Consortium (www.cytoscape.org)

  The Cytoscape Consortium is:
  - Institute for Systems Biology
  - University of California San Diego
  - Memorial Sloan-Kettering Cancer Center
  - Institut Pasteur
  - Agilent Technologies

  This library is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published
  by the Free Software Foundation; either version 2.1 of the License, or
  any later version.

  This library 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.  The software and
  documentation provided hereunder is on an "as is" basis, and the
  Institute for Systems Biology and the Whitehead Institute
  have no obligations to provide maintenance, support,
  updates, enhancements or modifications.  In no event shall the
  Institute for Systems Biology and the Whitehead Institute
  be liable to any party for direct, indirect, special,
  incidental or consequential damages, including lost profits, arising
  out of the use of this software and its documentation, even if the
  Institute for Systems Biology and the Whitehead Institute
  have been advised of the possibility of such damage.  See
  the GNU Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with this library; if not, write to the Free Software Foundation,
  Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
*/
package cytoscape.util;

import javax.swing.SwingUtilities;


/**
 * This is the 3rd version of SwingWorker (also known as
 * SwingWorker 3), an abstract class that you subclass to
 * perform GUI-related work in a dedicated thread.  For
 * instructions on using this class, see:
 *
 * http://java.sun.com/docs/books/tutorial/uiswing/misc/threads.html
 *
 * Note that the API changed slightly in the 3rd version:
 * You must now invoke start() on the SwingWorker after
 * creating it.
 */
public abstract class SwingWorker {
	private Object value; // see getValue(), setValue()
	private Thread thread;

	/**
	 * 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;
		}
	}

	private ThreadVar threadVar;

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

	/**
	 * Set the value produced by worker thread
	 */
	private synchronized void setValue(Object x) {
		value = x;
	}

	/**
	 * Compute the value to be returned by the <code>get</code> method.
	 */
	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());
				} 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();
		}
	}
}