SwingWorker.java

/*
 * Copyright (c) 2007 BUSINESS OBJECTS SOFTWARE LIMITED
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 *     * Redistributions of source code must retain the above copyright notice,
 *       this list of conditions and the following disclaimer.
 *  
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *  
 *     * Neither the name of Business Objects nor the names of its contributors
 *       may be used to endorse or promote products derived from this software
 *       without specific prior written permission.
 *  
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * SwingWorker.java
 * 
 * This file is based on SwingWorker.java, from Sun Microsystems,
 * found at:
 * 
 * http://java.sun.com/products/jfc/tsc/articles/threads/threads2.html
 */

package org.openquark.util.ui;

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()

    /** 
     * 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 final 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() {
        this (null);
    }

    /**
     * Start a thread that will call the <code>construct</code> method
     * and then exit.
     * 
     * @param threadName
     */
    public SwingWorker(String threadName) {
        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 = threadName == null ? new Thread (doConstruct) : new Thread(doConstruct, threadName);
        threadVar = new ThreadVar(t);
    }

    /**
     * Start the worker thread.
     */
    public void start() {
        Thread t = threadVar.get();
        if (t != null) {
            t.start();
        }
    }
}