public Future<V> schedule(Callable<V> task, Duration delay)
    {
        return schedule(task, delay.toMillis(), TimeUnit.MILLISECONDS);
    }
@throws RejectedExecutionException {@inheritDoc}
@throws NullPointerException       {@inheritDoc}
xmppserver/src/main/java/org/jivesoftware/util/ScheduledExecutorCompletionService.java