Triggers execution of the given callback, once the source terminates either
with a Cancel
or with a failure.
On Cancel, triggers Cancel on the given Promise.
On Cancel, triggers Continue on the given Promise.
Unsafe version of onComplete
that triggers execution synchronously
in case the source is already completed.
On Continue, triggers onComplete on the given Observer.
On Continue, triggers onComplete on the given Observer.
Internal extensions to Future[Ack] used in the implementation of Observable.