ArrayBlockingQueue - consumer thread blocks all threads on poll

Question

I have two threads - A is producing and B is consuming
Thread A calls offer with a 200 millisecond timeout.
Thread B calls poll with a 5 second timeout.
(I'm using an ArrayBlockingQueue)
The problem is that thread A does not continue to run until thread B finishes blocking for the full 5 seconds. Shouldn't the scheduler be allowing Thread A to run while B is blocked on an empty queue?
Thanks for any help!
Edited by: nw1968 on Jul 14, 2008 8:37 AM

Answer 1

In the following test, A doesn't wait for long for B and the while thing runs in under a second.
public class BlockingQueueTest {
    public static void main(String... args) {
        final BlockingQueue<Integer> q = new ArrayBlockingQueue<Integer>(5);
        Thread a = new Thread(new Runnable() {
            public void run() {
                try {
                    for (int i = 0; i < 100; i++) {
                        System.out.println(new Date() + ": Queue offer " + i);
                        while (!q.offer(i, 200, TimeUnit.MILLISECONDS))
                            System.out.println(new Date() + ": Queue full.");
                    q.offer(Integer.MIN_VALUE, 60, TimeUnit.SECONDS);
                } catch (Exception e) {
                    e.printStackTrace();
        Thread b = new Thread(new Runnable() {
            public void run() {
                try {
                    do {
                        Integer i = q.poll(5, TimeUnit.SECONDS);
                        if (i == Integer.MIN_VALUE)
                            break;
                        System.out.println(new Date() + ": ... poll => " + i);
//                        Thread.sleep(250);
                    } while (true);
                    System.out.println(new Date() + ": ... finished.");
                } catch (Exception e) {
                    e.printStackTrace();
        a.start();
        b.start();
}