Publisher behavior after cancellation of Subscription?

[Boereck]

Hello,

There seems to be no definition if a Publisher should notify a subscriber with onComplete or onError if the subscriber canceled the Subscribtion. Or should the Publisher silently accept the cancellation?
Did I overlook something or is there no defined behavior indeed?

Thanks,
Max

[Boereck]

I just found the set of rules in the master, especially rule 6 and 8 apply. So maybe I can refine the question: Do calls of Subscription::cancel represent a request for cancellation that has to be acknowledged by the Publisher, or does the Publisher have to regard a Subscription canceled as soon as Subscription::cancel is called? If there has to be an acknowledgment, the question would be via onError or onComplete? My intuition would be onError, since the Publisher did not complete regularly.

[ktoso]

Hi Max,
have a look at Rule 1.8 - after cancel() the Publisher should NOT signal onError nor onComplete, but this is not a "hard" requirement, because of the inherent race between signalling the cancelation and an in-flight OnComplete signal for example.

To answer your question directly - there is no need for the Publisher to "confirm that he got the cancellation", the Subscriber can start shutting down as soon as he's issued the cancelation. OnError and OnComplete are reserved for when the publisher terminates the Subscription.

[Boereck]

Hi Konrad,
Thanks for the clarification! I was just unsure what "canceled" meant in the context of rule 1.8. So if Subscription::cancel() is called the Subscriber is regarded as canceled, and calls to onError() or onComplete() should not be done (apart from concurrent signals already on the way).

Thanks again,
Max

[ktoso]

Glad I could help!

Somewhat related: In case you're working on an implementation, you may be interested in the soon-to-be-merged TCK: #91

[Boereck]

That will indeed be helpful. Thanks for pointing it out. I am working on a Publisher implementation only. I will run it against the relevant parts of the TCK, as soon as it is in the master.

[ktoso]

Great, looking forward to it! :-)