Question

I have a daemon thread which is started when a page is opened. The thread is then stopped when the page is closed. So in my class which holds the thread, I have it created like this:

class A {
 private static volatile boolean isStopped=false;

 //this method is called then the page is loaded
 public void testListener() {
   Thread listener = new Thread(new Runnable() {
      public void run() {
       while(!isStopped) {
        //perform listener event
       try {
         //after every event sleep for a while
         Thread.sleep(1000 *2)
       } catch(InterruptedException e){}
      }
     }
    });
 }
 listener.setName("Test-Server-Daemon");
 listener.setDaemon(true);
 listener.start();

 // reset back to false so thread can be restarted when the page load event,
 // call this method instance
 if (isStopped) {
   isStopped=false;
 }
}

 /**This is called when page is closed**/
 public static void stopListener() {
   isStopped=true;
  }
}

Upon investigation, I have noticed that when the page is closed and not opened again within say 30 seconds interval, the thread is gracefully stopped.

But when the page is closed and re-opened within say 2 seconds interval the old thread does not get stopped and hence runs simultaneously with a new one.

And so as you can see from below image, I have the same thread started again when I close and quickly open the page.

Do anyone knows how to prevent this from occurring?

I have tried using thread interrupt where I reset the mutex but no joy.

EDITED:

isStopped is volatile.

Answer 1

To follow on from @Jordão’s answer, the isStopped variable should be per thread. I would recommend using something like an AtomicBoolean and changing your thread code to be approximately:

public AtomicBoolean testListener() {
    final AtomicBoolean isStopped = new AtomicBoolean(false);
    Thread listener = new Thread(new Runnable() {
        public void run() {
            while(!isStopped.get()) {
                ...
            }
        }
    });
    listener.setName("Test-Server-Daemon");
    listener.setDaemon(true);
    listener.start();
    return isStopped;
}

Then back in your page controller you can do:

AtomicBoolean isStopped = testListener();
// do the page stuff
...
// when done stop the thread
isStopped.set(true);