How stop thread with infinite loop in finally block

Question

Sorry for my English.

I have a Thread with method:

  @Override
  public void run()
  {
    try
    {
      System.out.println( "Hello world" );
      Thread.sleep( 10 );
    }
    catch( InterruptedException e )
    {
      e.printStackTrace();
    }
    finally
    {
      while( true )
        System.out.println( "FINALLYYY" );
    }
  }

and I suggest, that this thread never can be stopped! After calling methods interrupt or stop - in finally block thread will start infinity loop.

How I can force the thread to stop?

score 1 · Answer 1 · edited Oct 13 '14 at 10:51

1

The Thread stop and interrupt methods are not the best way to solve this problem. Add a boolean variable to your thread and check it in your while statement.

For example:

  private volatile boolean keepGoing = true;

  public void stopTheThread() {
      keepGoing = false;
  }

  @Override
  public void run()
  {
    try
    {
      System.out.println( "Hello world" );
      Thread.sleep( 10 );
    }
    catch( InterruptedException e )
    {
      e.printStackTrace();
    }
    finally
    {
      while( keepGoing )
        System.out.println( "FINALLYYY" );
    }
  }

edited Oct 13 '14 at 10:51

PeterK

1,697
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answered Oct 13 '14 at 10:45

David ten Hove

2,748
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3

If you don't put volatile in the keepGoing var your loop could end never. – Carlos Verdes Oct 13 '14 at 10:47
1

@David ten Hove Yes, I know about it.... But I can't control or validate the code.. Because it's "external custom user's code", which should be executed on our server.. – Eugene Chipachenko Oct 13 '14 at 10:49
@EugeneChipachenko If that's the case, I think there is no solid way of stopping the thread in Java – David ten Hove Oct 13 '14 at 10:53
@CarlosVerdes Good catch. I missed that – David ten Hove Oct 13 '14 at 10:54

score 1 · Accepted Answer · answered Oct 13 '14 at 13:45

So... I Found next solution:

worker.interrupt();
while( worker.isAlive() )
  worker.stop();

It's not ideal solution, but in my case, it's best... Every call worker.stop - throw unchecked exception "ThreadDeath" and each finally block will be "skiped". It should stop the thread.

score 0 · Answer 3 · answered Oct 13 '14 at 10:55

In your current set up, you could stop the thread by calling the interrupt() method on the Thread that is executing.

Either way, to allow the Thread to terminate gracefully, you will have to expose a way to terminate that thread, either by exposing the thread so it can be interrupted, or by providing a 'kill switch' in the way suggested by David ten Hove.

score 0 · Answer 4 · edited May 23 '17 at 12:28

You may try to control how the user's thread is executed (at least while you control user's threads execution). For instance, you can use Future from concurrency package (don't forget to handle exceptions):
```
 ExecutorService executor = Executors.newSingleThreadExecutor();
 Future task = executor.submit(usersThread);

 try {
     task.get(1, TimeUnit.MINUTES);
 } finally {
     task.cancel(true);
 }
```
If you can't control the code inside the Thread, then you may control the code, which is used from it. For instance, consider the following approaches:
- If you can run that Thread in a groovy context, then you can reassign methods, which are called from the Thread. Actually, you can deny everything and pass every call through your custom handler for unknown methods.
- If you are sure, what is called from the Thread, then you can pick up some hijacks (consider an example in this question).

How stop thread with infinite loop in finally block

4 Answers4