public Future<V> poll(long timeout, @Nonnull TimeUnit unit)
        throws InterruptedException {
        return completionQueue.poll(timeout, unit);
    }
@throws RejectedExecutionException {@inheritDoc}
@throws NullPointerException       {@inheritDoc}
xmppserver/src/main/java/org/jivesoftware/util/ScheduledExecutorCompletionService.java