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javamultithreadinginterrupt

What is the reason for interrupting the thread in the catch clause of InterruptedException?

I'm reading J. Bloch's Effective Java and now I'm at the section which explains about Concurrency. The writer has provided the following example (Some modifications were applied to make it simpler):

Runnable action;
//...
executor.execute(new Runnable() {
    public void run() {
    ready.countDown();
        try {
            start.await();
            action.run();
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt(); // <------- Here
        } finally {
            done.countDown();
        }
    }
});

It's not clear that why we interrupt the Thread that already was interrupted? Couldn't you get a little explanation about what kind of troubles we may run into if we omit such interrupting?

Solution

  • Yes, it's right.

    When an InterruptedException is thrown from a blocking method, the interrupt flag is cleared.

    The right thing to do is to reset the interrupt flag (i.e. interrupt again) and stop running ASAP. Resetting the interrupt flag is necessary to let the executor (or any other calling code) know that the thread has been interrupted, and thus allow it to stop running.