Why is Akka Streams swallowing my exceptions?

Question

Why is the exception in

import akka.actor.ActorSystem
import akka.stream.ActorMaterializer
import akka.stream.scaladsl.Source

object TestExceptionHandling {
  d         


        

Answer 1

I had similar questions when I started using akk-streams. Supervision.Decider helps but not always.

Unfortunately it doesn't catch exceptions thrown in ActionPublisher. I see it handled, ActorPublisher.onError is called but it doesn't reach Supervision.Decider. It works with simple Stream provided in documentation.

Errors also don't reach actor if I use Sink.actorRef.

And for the sake of experiment I tried following sample

val stream = Source(0 to 5).map(100 / _)
stream.runWith(Sink.actorSubscriber(props))

In this case exception was caught by Decider but never reached actor subscriber.

Overall I think it's inconsistent behavior. I cannot use one mechanism for handling errors in Stream.

My original SO question: Custom Supervision.Decider doesn't catch exception produced by ActorPublisher

And here is akka issue where it's tracked: https://github.com/akka/akka/issues/18359