CODEWITHSUNDEEP
javamultithreadingthread-safetyjava-threadslegacy
Raghav
Raghav

Reputation: 3058

How to interrupt or kill a java thread while it's running

After reading several SO posts on how to kill a Java thread, I fairly understand why stop is unsafe and how to handle the graceful stop.

But the solutions are targeting towards UI threads where repainting is the problem and not really a long running - blocking process executed by a thread.

Links:

How do you kill a Thread in Java? https://docs.oracle.com/javase/1.5.0/docs/guide/misc/threadPrimitiveDeprecation.html

One precise point that I fail to understand from the solutions or examples is what is the long-running-part the samples are trying to simulate.

Eg: In this following code, what if I set the interval to INT.MAX.

public void run() {
        Thread thisThread = Thread.currentThread();
        while (blinker == thisThread) {
            try {
                thisThread.sleep(interval);  // This might take forever to complete, 
                                             // and while may never be executed 2nd time.

                synchronized(this) {
                    while (threadSuspended && blinker==thisThread)
                        wait();
                }
            } catch (InterruptedException e){
            }
            repaint();
        }
    }

    public synchronized void stop() {
        blinker = null;
        notify();
    }

The reason am asking for this use case is that, I have a bug in a legacy code base that runs another executable in a Thread. Now the ask if the user wishes to stop the thread, we would need to kill this thread, and the executable which is part of this thread automatically gets killed.

Upvotes: 2

Views: 3490

Answers (1)

Andy Turner
Andy Turner

Reputation: 140309

The way you stop a thread is by asking it - nicely - to stop. It's up to the code the thread is running to listen for and act on that request.

Specifically, the way you do it is to interrupt the thread. Your code checks for the interruption - Thread.sleep and Object.wait will throw InterruptedException if the thread is interrupted before or during their execution; but you catch the interruption, and ignore it, so you won't act on it.

Instead of this:

while (condition) {
  try {
    Thread.sleep(...);

    wait();
  } catch (InterruptedException e) {
  }
}

Put the interruption outside the loop:

try {
  while (condition) {
    Thread.sleep(...);
    wait();
  }
} catch (InterruptedException e) {
}

then the loop terminates if it is interrupted.

Upvotes: 4

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