package commons.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()
private Thread thread;

/** 
 * 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();
   }
}
}