Specifically, the documentation of SubscriberApi.pull says "The client may cancel the request if it does not wish to wait any longer for the response." This is currently only possible if the api caller uses the ApiCallable, and calls cancel on the ClientCall. The other method forms still make reference to canceling though, even though it's not possible. Possibly the interface needs to be updated somehow, or also the documentation needs to be adjusted.
Specifically, the documentation of SubscriberApi.pull says "The client may cancel the request if it does not wish to wait any longer for the response." This is currently only possible if the api caller uses the ApiCallable, and calls cancel on the ClientCall. The other method forms still make reference to canceling though, even though it's not possible. Possibly the interface needs to be updated somehow, or also the documentation needs to be adjusted.