swingworker.java

WAP Stack implementation jwap.sourceforge.net

package net.sourceforge.jwap.util;

import javax.swing.SwingUtilities;


public abstract class SwingWorker {
    private Object value; 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.
 */
    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 the worker thread.
 */
    public void start() {
        Thread t = threadVar.get();

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

    /**
 * 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;
        }
    }
}