Thread concurrency problem - how to know when thread is dead?

Question

My applet uses a thread to draw an iteration graph step by step.
The user as the option of pressing two buttons:
- PLAY button - iteration Points are stored in an arrayList and drawn step by step (a sleeping time follows each step) (drawIterations thread)
- TO_END button - iteration Points are all stored in the arrayList (swingworker thread) and after all of them have been stored the graph is drawn instantly.
I have problems in this situation:
When executing the PLAY-button thread, if the user presses TO_END button, the remaining graph lines should draw instantly. Sometimes I get more points on the graph than I should. It seems that the PLAY thread, which I stop when TO_END buton is pressed, still remains storing new points into the arrayList concurrently to the new thread created after TO_END button was pressed .
Any ideas?
I'm already using synchronization.
private volatile Thread drawIterations;
public void playButtonClick(JToggleButton btn) {
     pointSet1 = new ArrayList<Point2D.Double>();
     if (drawIterations == null) drawIterations = new Thread(this,   "drawIterations");
     drawIterations.start();
public void toEndButtonClick(JToggleButton btn) {
     stopThread() ;
     pointSet1 = new ArrayList<Point2D.Double>();
     computeIterationGraphPointsAndRefreshGraph();
public synchronized void stopThread() {
     drawIterations = null;
     notify();
private void computeIterationGraphPointsAndRefreshGraphs() {
     SwingWorker worker = new SwingWorker() {
          public Object construct() {
               // compute all iteration points
                     //repaint graph
     worker.start();
}Is there a way of testing if a thread is actually dead after setting the thread object to null??

Answer 1

In general, a Thread keeps running until it's run
method completes. Threads don't stop when their
handle is set to null. Your run method should
constantly be checking on a variable to know when to
stop running and exit the run method. In this case,
you could check on the drawIterations variable to see
if it's null.<br>
<br>Even using the following line on my run method I get the the same problem:
<br>
<br>while (myThread == drawIterations && drawIterations!=null && halfStep < 2 * totalIterations) {
<br>...
<br>
<br>Here's the whole method:
<br>(actually there are 2 graphs being drawn and the second is only refreshed every 2 steps:)
<br>
<br>     <br>public void run() {
     <br>  Thread myThread = Thread.currentThread();
     <br>  int totalIterations = transientIterations +iterationsToDraw ;
          <br>  while (myThread == drawIterations && drawIterations!=null && halfStep < 2 * totalIterations) {
          <br>     computeNextHalfIterationGraphPoint( );
          <br>      if (!TRANSIENT_IS_ENABLED || halfStep >= 2*transientIterations ) {// is     not in transient calculations
          <br>                       graphArea1.repaint();
          <br>                       if (halfStep%2 ==0 ) graphArea2.repaint();
          <br>                       if (halfStep < 2*totalIterations){//no need to execute the following block if at last iteration point
               <br>                         if (lastIterationPointsFallOutsideGraphArea(toEndCPButtonActive)) break;
                    <br>          try {
                         <br>                      Thread.sleep(sleepingTimeBetweenHalfIterationRendering);
                         <br>                      if (threadInterrupted ){//if clause included to avoid stepping into a synchronized block if unnecessary
                              <br>                        synchronized (this) {
                                   <br>                          while (threadInterrupted && myThread==drawIterations ) wait();
                                                  <br>    }
<br>                                               }
     <br>                                   } catch (InterruptedException e) {
          <br>                                     break;
               <br>                         }     
                    <br>               }
<br>                            }
     <br>        stopThread();
     <br>     }
<br>