Question

Let us suppose that I have a thread that consumes items produced by another thread. Its run method is as follows, with inQueue being a BlockingQueue

boolean shutdown = false;
while (!shutdown) {
    try {
        WorkItem w = inQueue.take();
        w.consume();
    } catch (InterruptedException e) { 
        shutdown = true;
    }
}

Furthermore, a different thread will signal that there are no more work items by interrupting this running thread. Will take() throw an interrupted exception if it does not need to block to retrieve the next work item. i.e. if the producer signals that it is done filling the work queue, is it possible to accidentally leave some items in inQueue or miss the interrupt?

Answer 1

A good way to signal termination of a blocking queue is to submit a ‘poison’ value into the queue that indicates a shutdown has occurred. This ensures that the expected behavior of the queue is honored. Calling Thread.interupt() is probably not a good idea if you care about clearing the queue.

To provide some code:

boolean shutdown = false;
while (!shutdown) {
    try {
        WorkItem w = inQueue.take();
        if (w == QUEUE_IS_DEAD)
          shutdown = true;
        else
          w.consume();
    } catch (InterruptedException e) { 
        // possibly submit QUEUE_IS_DEAD to the queue
    }
}