Java thread doesn't stop/interrupt

Question

I'm trying to terminate a thread but it doesn't interrupt or stop. All of this are part of controller of a software called Webots. I use this to simulate a multi robot system. In the controller of each robot, I start a thread which receive messages through robots receivers. This thread must start at first, and terminate when simulation ends.

The run method for this thread look like this:

public void run() {
    while (true)
    {
        String M = recieveMessage();
        char[] chars = M.toCharArray();
        if(chars[0]==robotName||chars[0]=='0')
            messages.add(M);                                                
     }
}

In the main controller I have code that look like this:

MessageThread MT = new MessageThread(messages, receiver,getName());
MT.start();
for (int i = 0; i < 100; i++)
{
    try
    {
         Thread.sleep(25);  } catch (InterruptedException e) {      e.printStackTrace();    }
    System.out.println(messages.get(messages.size()-1));                
 }
 MT.interrupt();//MT = null;
 System.out.println(MT.interrupted());

It's not important what I do in my main controller, so don't judge it. For example, messages is an ArrayList. It's like a buffer which MT put messages in and the main thread reads from. I use it because the receiver and emitter are not synchronized.

If I call interrupt() or MT = null but interrupted() it returns false and MT continues to run. Is there anything wrong in my code?

I read some topics like:

http://docs.oracle.com/javase/1.5.0/docs/guide/misc/threadPrimitiveDeprecation.html

How do you kill a Thread in Java?

interrupt() doesn't work

Java: How interrupt/stop a thread?

and so on but I couldn't find any useful answer.

Edit

Thanks everyone, I've made changes to my code. I added this to the MessageThread class:

private volatile boolean isRunning = true;

Then I used while(isRunning) instead of while(true) and I added

public void kill()
{
    isRunning = false;
}

and called MT.kill() instead of MT.interrupt().

It worked but I couldn't find out what's wrong with interrupt(). I read the link which @ExtremeCoders recommended. However, I'm still confused. It says "a thread must support its own interruption". So do I have to overwrite the interrupt() method? I can't call interrupt to terminate a thread?

Thanks again.

What do you think `interrupt` does? And what are you trying to achieve? — Sotirios Delimanolis, Dec 28 '13 at 18:38
`interrupt` does not work the way you think. You have to check `interrupted` flag in your loop and break accordingly. See ***[this](http://docs.oracle.com/javase/tutorial/essential/concurrency/interrupt.html)*** link — Extreme Coders, Dec 28 '13 at 18:40
So how can I stop MT thread? I know Thread.stop() has some problems. In java docs, they stop thread by setting it to null. I tried it but it doesn't work anyway. — Taher, Dec 28 '13 at 18:43
@Taher Instead of a `while(true)` loop use `while(!Thread.interrupted())` — Extreme Coders, Dec 28 '13 at 18:46

score 5 · Answer 1 · answered Dec 28 '13 at 19:44

Interrupting a thread just sets a flag on the thread. If the thread never checks the flag, it won't respond. By creating your own boolean member, you've duplicated that functionality unnecessarily.

Here's the general pattern for what you are trying to do:

@Override
public void run() {
  while(!Thread.interrupted() {
    /* Do something. */
  }
  Thread.currentThread().interrupt();
}

This will allow you to call MT.interrupt() as you expected. It's better than creating your own flag and custom method to set it: you can use your Runnable task with high-level tools like ExecutorService and cancellation will work because you used the standard API; same is true for interruption of an entire ThreadGroup.

Calling Thread.interrupted() clears the interruption status of a thread; we set it by calling Thread.currentThread().interrupt(), the status is set again so that callers of run() can detect the interrupted state. This might not always be desirable however.

Thanks, as @ExtremeCoders suggested, I used while(!Thread.interrupted()) but MT Thread didn't stop!!! So I decide to define my own flag. — Taher, Dec 28 '13 at 20:10
@Taher Did you use that together with a call to `MT.interrupt()`? Because it will definitely work; if it didn't, you did something wrong. — erickson, Dec 28 '13 at 20:26
Yes, I did and I surprised why MT is still running. I changed my while loop with while(!Thread.interrupted()) and I added hread.currentThread().interrupt(); after while and I called MT.interrupt() in main thread. — Taher, Dec 28 '13 at 20:35

Java thread doesn't stop/interrupt

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