src/main/java/io/reactivex/subscribers/DefaultSubscriber.java
protected final void request(long n) {
        Subscription s = this.upstream;
        if (s != null) {
            s.request(n);
        }
    }
protected final void request(long n) {
        Subscription s = this.upstream;
        if (s != null) {
            s.request(n);
        }
    }
Requests from the upstream Subscription.
@param n the request amount, positive