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package edu.rice.cs.util.swing;

import java.awt.EventQueue;

/** SwingWorker, adapted from Sun's Java Tutorial. 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.

* @version $Id: SwingWorker.java 5594 2012-06-21 11:23:40Z rcartwright $

*/

public abstract class SwingWorker {

private volatile 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 volatile Thread _thread;

ThreadVar(Thread t) { _thread = t; }

Thread get() { return _thread; }

void clear() { _thread = null; }

}

private volatile ThreadVar _threadVar;

/** Gets the value produced by the worker thread, or null if it hasn't been constructed yet. */

protected Object getValue() { return _value; }

/** Sets the value produced by worker thread. */

private void setValue(Object x) { _value = x; }

/** Compute the value to be returned by the <code>get</code> method. */

public abstract Object construct();

/** Called from 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()); }

catch (final RuntimeException e) {

// Throw the exception in the event dispatching thread.

EventQueue.invokeLater(new Runnable() { public void run() { throw e; } });

throw e;

}

catch (final Error e) {

// Throw the error in the event dispatching thread.

EventQueue.invokeLater(new Runnable() { public void run() { throw e; } });

throw e;

}

finally { _threadVar.clear(); }

EventQueue.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();

}

}