class QueueDrainObserver extends QueueDrainSubscriberPad2 implements Observer<T>, ObservableQueueDrain<U, V> {

    @Override
    public final boolean enter() {
        return wip.getAndIncrement() == 0;
    }

    public  QueueDrainObserver(Observer<? super V> actual, SimplePlainQueue<U> queue);

}