CODEWITHSUNDEEP
akka
user2684301
user2684301

Reputation: 2620

Akka Terminate Dead Letters

I completed the first Akka assignment for the Coursera Reactive Programming Class (week five - binary trees).

My question is about Akka itself.

My app runs correctly, but I notice a lot of non-fatal dead letter warnings. Here is one:

[INFO] [01/16/2014 15:09:41.668] [PostponeSpec-akka.actor.default-dispatcher-23] [akka://PostponeSpec/user/$c/$b/$a/$b/$a/$a/$b/$b/$a/$a] Message [akka.dispatch.sysmsg.Terminate] from Actor[akka://PostponeSpec/user/$c/$b/$a/$b/$a/$a/$b/$b/$a/$a#570299303] to Actor[akka://PostponeSpec/user/$c/$b/$a/$b/$a/$a/$b/$b/$a/$a#570299303] was not delivered. [2] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.

I notice others have asked about this, and the official answer is that this isn't a problem, it's just verbose information that can be ignored and hidden by updating the logging settings.

I understand the advice to simply ignore this, but it still seems like a sloppy flaw on Akka's part. In this simple learning exercise, I am confident that my actors never get sent a message after they initiate a graceful shutdown. Akka should not be putting anything in the dead letter queue in these idealized circumstances. What is the justification for these dead letters? I also see it that the dead letter message isn't one that my app explicitly sends, but an internal message.

Upvotes: 1

Views: 1338

Answers (1)

Eyal Farago
Eyal Farago

Reputation: 63

As someone who took the course as well,and asked questions in the course feed I recall the following: the child actor may decide to stop itself,but its parent may decide to do the same thing. At this point there's an inherent race condition between the parent's termination and the delivery of the Terminate(child) message,if the parent managed to stop itself prior to receiving the message it will end in the dead letters queue.

Upvotes: 1

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