Signaling a thread to terminate whenever it reached a stable situation

Question

Suppose I have two threads A and B, both running. Suddenly B decides to terminate A, and thus A should terminate ASAP. I don't want A to terminate instantly, but when it has reached a stable state.

A naive solution is to use a shared variable terminatePlease, which A would check for every time it reaches a stable state.

A prototype of the code looks like:

class A extends Thread {
    boolean terminatePlease;

    public void run() {
        while (true) {
            if (terminatePlease)
                return;
            doUninterruptableTasks();
        }
    }
}

Is there any other concurrency pattern to handle such situations?

Answer 1

That's the idea, yes. The boolean should be volatile to make this solution work though.

But you don't even need this flag, because each thread has one already: the interrupted flag. So you could just call a.interrupt(); from thread B, and have your thread A do the following:

public void run() {
    while (!Thread.currentThread().isInterrupted()) {
        doUninterruptableTasks();
    }
}

Note, though, that interrupting a thread blocked in a waiting state will make the blocking method throw an InterruptedException, in order to stop running ASAP. If you don't want that, then use a volatile flag.