Exception in thread "Thread-2" java.lang.IllegalStateException: peekedSequence 18, lastPeekedSequence 25
	at com.wjybxx.fastjgame.concurrenttest.SpmcArrayQueuePeekTest$Peeker.run(SpmcArrayQueuePeekTest.java:111)

public class SpmcArrayQueuePeekTest {

    private static volatile boolean stop = false;

    public static void main(String[] args) throws InterruptedException {
        // Smaller capacity helps test
        MessagePassingQueue<Long> messageQueue = new SpmcArrayQueue<>(8);
        new Producer(messageQueue).start();
        new Consumer(messageQueue).start();
        new Peeker(messageQueue).start();

        try {
            Thread.sleep(10 * 1000);
        } finally {
            stop = true;
        }
    }

    private static class Producer extends Thread {

        final MessagePassingQueue<Long> messageQueue;

        long sequence = 0;

        Producer(MessagePassingQueue<Long> messageQueue) {
            this.messageQueue = messageQueue;
        }

        @Override
        public void run() {
            while (!stop) {
                if (messageQueue.offer(sequence)) {
                    sequence++;
                }
            }
        }
    }

    private static class Consumer extends Thread {

        final MessagePassingQueue<Long> messageQueue;

        private Consumer(MessagePassingQueue<Long> messageQueue) {
            this.messageQueue = messageQueue;
        }

        @Override
        public void run() {
            while (!stop) {
                messageQueue.poll();
                // wait producer fill
                try {
                    Thread.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }

    }

    private static class Peeker extends Thread {

        final MessagePassingQueue<Long> messageQueue;
        long lastPeekedSequence;

        private Peeker(MessagePassingQueue<Long> messageQueue) {
            this.messageQueue = messageQueue;
        }

        @Override
        public void run() {
            while (!stop) {
                final Long peekedSequence = messageQueue.peek();
                if (peekedSequence == null) {
                    continue;
                }

                if (peekedSequence < lastPeekedSequence) {
                    String msg = String.format("peekedSequence %s, lastPeekedSequence %s", peekedSequence, lastPeekedSequence);
                    throw new IllegalStateException(msg);
                }

                lastPeekedSequence = peekedSequence;
            }
        }
    }
}