"message unhandled" logged when using Behaviors#transformMessages

Akka Actors
1

I would expect no “message unhandled” messages in the log when using akka.actor.typed.javadsl.Behaviors#transformMessages ?

2

Actual log message: 09:44:21,458 INFO [LocalActorRef] Message [MyMessage] from Actor[akka://sys@127.0.0.1:2552/deadLetters] to Actor[akka://sys#-2054150271] was unhandled. [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 think this is not really related to Behaviors#transformMessages because the log message appears only once, after starting the system. Subsequent message traffic does not generate “unhandled” log messages.

3

Which Akka version is that. I just verified with one of the tests we have that it is logged as unhandled dead letter.

4

Akka 2.6.3

5

That is strange. Then it would good if you can provide an example of how to reproduce it, because that is not what I’m seeing.

6

This is my utility method:

	public static <W, N extends W> Behavior<W> receiveOnly(
			Class<W> outerMsgClass,
			Class<N> innerMsgClass,
			Function<N, Behavior<N>> onMessage) {

		return transformMessages(outerMsgClass, receiveMessage(onMessage::apply), selector -> {
			return selector.match(innerMsgClass, m -> m);
		});
	}

Message class hierarchy:

class JobProgressUpdated implements JobProgressEvent

Behavior using transformMessages:

	Behavior<JobProgressEvent> jobActivityConfirmation(ActorRef<ConfirmJobActivity> target) {
		return receiveOnly(JobProgressEvent.class, JobProgressUpdated.class, event -> {
			target.tell(new ConfirmJobActivity(event.getJobId()));
			return same();
		});
	}

Equivalent behavior without using transformMessages:

	Behavior<JobProgressEvent> jobActivityConfirmation(ActorRef<ConfirmJobActivity> target) {
		return receive(JobProgressEvent.class)
				.onMessage(JobProgressUpdated.class, event -> {
					target.tell(new ConfirmJobActivity(event.getJobId()));
					return same();
				})
				.onAnyMessage(ev -> same())
				.build();
	}

Actor factory method (called from parent EventsourcedBehavior (see below)):

	ActorRef jobActivityConfirmer(ActorContext<JobExecutionCommand> ctx) {
		return toClassic(ctx.spawn(jobActivityConfirmation(ctx.getSelf().narrow()), "JobActivityConfirmer-" + anyString(5)));
	}

Creation of parent EventSourced behavior (JobExecution):

	Behavior<JobExecutionCommand> jobExecution(JMS jms) {
		return withTimers(scheduler -> {
			scheduler.startTimerWithFixedDelay(new ExpireOverrunningJobs(), overrunningJobsCheckoutInterval);

			return setup(ctx -> {
				jms.distributedPubSub().subscribe(ProgressTopicName, jobActivityConfirmer(ctx));
				return new JobExecution(jms, ctx);
			});
		});
	}

I can confirm that “message unhandled” is logged only if using Behaviors#transformMessages. It is only logged when I’m performing the initial test (after starting the system). Subsequent tests do not produce “message unhandled” log message.

7

Note that you can configure how many are logged: https://github.com/akka/akka/blob/master/akka-actor/src/main/resources/reference.conf#L56

I think it’s the same setting for unhanded.
You may also use https://github.com/akka/akka/blob/master/akka-actor/src/main/resources/reference.conf#L66

8

Thanks. I have applied log-dead-letters = on
and now the unhandled messages are logged every time I perform the test (with transformMessages).