Under what conditions will BlockingQueue.take throw interrupted exception?

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
    }
}

According to javadoc, the take() method will throw InterruptedException if interrupted while waiting.

I wondered about the same thing and reading the javadoc for take() I believed that it would throw an interrupted exception only after having taken all the items in the queue, since if the queue had items, it would not have to "wait". But I made a small test:

package se.fkykko.slask;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.atomic.AtomicLong;

public class BlockingQueueTakeTest {

public static void main(String[] args) throws Exception {
    Runner t = new Runner();
    Thread t1 = new Thread(t);
    for (int i = 0; i < 50; i++) {
        t.queue.add(i);
    }
    System.out.println(("Number of items in queue: " + t.queue.size()));
    t1.start();
    Thread.sleep(1000);
    t1.interrupt();
    t1.join();
    System.out.println(("Number of items in queue: " + t.queue.size()));
    System.out.println(("Joined t1. Finished"));

}

private static final class Runner implements Runnable {
    BlockingQueue<Integer> queue = new ArrayBlockingQueue<Integer>(100);
    AtomicLong m_count = new AtomicLong(0);

    @Override
    public void run() {
        try {
            while (true) {
                queue.take();
                System.out.println("Took item " + m_count.incrementAndGet());
                final long start = System.currentTimeMillis();
                while ((System.currentTimeMillis() - start) < 100) {
                    Thread.yield(); //Spin wait
                }
            }
        }
        catch (InterruptedException ex) {
            System.out.println("Interrupted. Count: " + m_count.get());
        }
    }
}

}

The runner will take 10-11 items and then finish i.e. take() will throw InterruptedException even if there still is items in the queue.

Summary: Use the Poison pill approach instead, then you have full control over how much is left in the queue.