[concurrency-interest] j.u.c.Flow.Subscription.request clarification and javadoc typos

Pavel Rappo pavel.rappo at gmail.com
Fri Sep 11 10:45:09 EDT 2015


Hi, I have two questions if I may.

1. Given the spec of j.u.c.Flow.Subscription.request method:

    /**
     * Adds the given number {@code n} of items to the current
     * unfulfilled demand for this subscription.  If {@code n} is
     * negative, the Subscriber will receive an {@code onError}
     * signal with an {@link IllegalArgumentException} argument.
     * Otherwise, the Subscriber will receive up to {@code n}
     * additional {@code onNext} invocations (or fewer if
     * terminated).
     *
     * @param n the increment of demand; a value of {@code
     * Long.MAX_VALUE} may be considered as effectively unbounded
     */
    public void request(long n);

I was wondering how flexible this is. It doesn't seem to allow stating the
demand in any other units than items (or number of onNext(T) invocations, which
I assume is the same).
One of the reviewers of WebSocket API has mentioned that some people "receive a
ByteBuffer, but backpressure on the number of bytes consumed" and that the
choice of units is actually "an implementation detail" [1]. Is that so?

I can understand the situation when one would have a function f(units) that
would map a number of back-pressure units to a number of onNext() calls (or
items). So one could always know how many onNext() calls to expect. But what if
this is not the case? For example an item is a ByteBuffer of unknown size?

2. A minor thing. In the javadoc to j.u.c.SubmissionPublisher:

    * {@link Flow.Subscriber#onNext onNext}, but exceptions in methods
    * {@link Flow.Subscriber#onSubscribe onSubscribe},
    * {@link Flow.Subscriber#onError #onError} and
    * {@link Flow.Subscriber#onComplete #onComplete} are not recorded or

I believe '#' characters are typos at the end of the third and the fourth lines.
Thanks.

-Pavel

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