How to Gracefully Terminate a Java Thread?

How to Gracefully Terminate a Java Thread

When encountering a long-running thread that must be stopped mid-execution, it's crucial to do so gracefully to avoid unpredictable consequences.

To achieve this, a common approach is to introduce a control variable within the thread's run() method. This variable, typically a boolean flag, acts as a sentinel to signal the termination request.

Consider the following example:

class MyThread extends Thread {
  volatile boolean finished = false;

  public void stopMe() {
    finished = true;
  }

  @Override
  public void run() {
    while (!finished) {
      // Perform the necessary actions
    }
  }
}

From the main thread, you can gracefully halt the execution by calling the stopMe() method:

MyThread myThread = new MyThread();
myThread.start();

// Wait some time to simulate work
Thread.sleep(500);

myThread.stopMe();

Previously, Java had a stop() method, but it was declared unsafe due to its potential to corrupt the thread's state and unlock acquired locks. Therefore, using the control variable approach is the recommended way to ensure a clean and controlled thread termination.

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