Application: gvSIG desktop

/**

 * gvSIG. Desktop Geographic Information System.

 *

 * Copyright (C) 2007-2013 gvSIG Association.

 *

 * This program 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.

 *

 * This program 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, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,

 * MA  02110-1301, USA.

 *

 * For any additional information, do not hesitate to contact us

 * at info AT gvsig.com, or visit our website www.gvsig.com.

 */

package org.gvsig.utils.swing.threads;

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 and examples of 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()

    /** 

     * 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();

        }

    }

}