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I have some actors that kill themselves when idle or other system constraints require them to. The actors that have ActorRefs to them are watching for their Terminated(ref), but there is a race condition of messages meant for the actors being sent before the termination arrives and I'm trying to figure out a clean way to handle that.

I was considering subscribing to DeadLetter and using that to signal the sender that their ref is stale and that they need to get or spawn a new target ActorRef.

However, in Akka Typed, I cannot find any way to get to dead letters other than using the untyped co-existence path, so I figure I'm likely approaching this wrong.

Is there a better pattern for dealing dead downstream refs and re-directing messages to a new downstream refs, short of requiring some kind of ack hand-shake for every message?

Arne Claassen
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Consider dead letters as a debugging tool rather something to use to implement delivery guarantees with (true for both Akka typed and untyped).

If an actor needs to be certain that a message was delivered the message protocol will need to include an an ack. To do resending the actor will also need to keep a buffer for in-flight/not yet acknowledged messages to be able to resend.

We have some ideas on an abstraction for different levels of reliability for message delivery, we'll see if that fits in Akka 2.6 or happens later though, prototyped in: https://github.com/akka/akka/pull/25099

johanandren
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  • You're right. Shouldn't try to turn `DeadLetter` into a delivery guarantee tool and just explicitly go to an Ack pattern – Arne Claassen May 27 '19 at 16:39