Subscription rules

The following interface describes the Subscription notation:

public interface Subscription {
    public void request(long n);
    public void cancel();
}

The rule number 3.2 says, Subscription must allow the Subscriber to call Subscription.request synchronously from within onNext or onSubscribe. It talks about preventing both Publisher and Subscriber by restricting posting of the message only when  Publisher gets the signal for a further request from Subscriber. This happens in a synchronous manner to avoid a stack overflow.

In a similar context, another rule, number 3.3, states, Subscription.request() must place an upper bound on possible synchronous recursion between Publisher and Subscriber. It complements rule 3.2 in a sense by deciding an upper limit in the recursive interaction between Publisher and Subscriber in the form of the onNext() and request() call. Setting the upper limit will avoid blowing out when calling a thread stack. The rules starting from number 3.5 to 3.15 describe the behavior of cancelling and completing the request.