SwingWorker.java

/*
 * Copyright (C) 2004 Anthony Smith
 *
 * 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 2
 * 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., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 * ----------------------------------------------------------------------------
 * TITLE $Id$
 * ---------------------------------------------------------------------------
 *
 * --------------------------------------------------------------------------*/
package opendbcopy.swing;

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.  PLEASE NOTE: I have
 * modified SwingWorker slightly from the original source
 */
public abstract class SwingWorker {
    private Object    value; // see getValue(), setValue()
    private ThreadVar threadVar;

    /**
     * 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);
    }

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

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

    /**
     * Compute the value to be returned by the <code>get</code> method.
     *
     * @return DOCUMENT ME!
     */
    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();
    }

    /**
     * DOCUMENT ME!
     *
     * @return DOCUMENT ME!
     */
    public boolean isInterrupted() {
        Thread t = threadVar.get();

        if (t != null) {
            return t.isInterrupted();
        } else {
            return true;
        }
    }

    /**
     * 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 the worker thread.
     */
    public void start() {
        Thread t = threadVar.get();

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

    /**
     * DOCUMENT ME!
     *
     * @param millis DOCUMENT ME!
     *
     * @throws InterruptedException DOCUMENT ME!
     */
    public void have_a_break(int millis) throws InterruptedException {
        Thread t = threadVar.get();
        t.wait(millis);
    }

    /**
     * Class to maintain reference to current worker thread under separate synchronization control.
     */
    private static class ThreadVar {
        private Thread thread;

        /**
         * Creates a new ThreadVar object.
         *
         * @param t DOCUMENT ME!
         */
        ThreadVar(Thread t) {
            thread = t;
        }

        synchronized Thread get() {
            return thread;
        }

        synchronized void clear() {
            thread = null;
        }
    }
}