public void Subscribe(ISubscriber <T> s)
        {
            var parent = new OrderedJoin(s, source.Parallelism, prefetch);

            s.OnSubscribe(parent);
            source.SubscribeMany(parent.subscribers);
        }
 internal InnerSubscriber(OrderedJoin parent, int prefetch)
 {
     this.parent   = parent;
     this.prefetch = prefetch;
     this.limit    = prefetch - (prefetch >> 2);
 }