Hi guys, Is CompletableDeferred’s await method coo...

# coroutines

[Nemanja Scepanovic]

Hi guys,
Is CompletableDeferred’s await method cooperative, meaning if wrapping context gets CanellationException would this completable deferred’s job be automatically completed or not? If not, what is the best way of making it cooperative?
Thanks 🙂

[Daniele Segato]

a cancellation is propagated to children.

so when you cancel a parent of the scope used to create the deferred that is cancellated to.

your await() will receive a cancellation exception if that happens.

I'm not sure if I answered your question

[Nemanja Scepanovic]

Hmm, but the if onCompletion{} is set, why isn’t it being invoked after cancellation is propagated? Shouldn’t completableDeferred object’s state become COMPLETED when parent’s cancellation exception is propagated? Or i misinterpreted how onCompleted{} behaves?

[araqnid]

CompletableDeferred isn’t automatically linked to a Job.
A Deferred that is implemented by async{} will complete exceptionally if the async coroutine is cancelled, but a CompletableDeferred needs to be completed explicitly.
So when you say “wrapping context”, how is this being linked to the CompletableDeferred? Are you creating it with a parent explicitly?

[Nemanja Scepanovic]

By wrapping context I meant viewModelScope inside which completableDeferred logic is called (this is just a simplification but you get the point).

[Nemanja Scepanovic]

Ok, so only if completableDeferred is completed explicitly though complete or completeExceptionally will the invokeOnCompletion be called?

[araqnid]

I believe so, and I presume that if you link the CompletableDeferred to a parent Job (CompletableDeferred(parent=coroutineContext[Job]!!)), then the parent job being cancelled will automatically complete it with CancellationException

[Nemanja Scepanovic]

That might actually work. I guess I never though of it that way. Thanks man!

[araqnid]

https://pl.kotl.in/ZQIDostDh

[Nemanja Scepanovic]

Great success! 😄