public interface Publisher<T>
A Publisher can serve multiple Subscribers subscribed subscribe(Subscriber) dynamically
at various points in time.
subscribe(Subscriber<? super T> s)
void subscribe(Subscriber<? super T> s)
This is a "factory method" and can be called multiple times, each time starting a new Subscription.
Each Subscription will work for only a single Subscriber.
A Subscriber should only subscribe once to a single Publisher.
If the Publisher rejects the subscription attempt or otherwise fails it will
signal the error via Subscriber.onError(java.lang.Throwable).