Restarting Akka Actor with a new State

[Joe San]

I have a scenario where I have to restart a child Actor from within a parent actor. The restart should happen with the following rules:

1. The start should happen only after stop has been completed
2. Both the stop and start should happen asynchronously

I now have the following scenario:

In my parent Actor, I have a Monix Observable which is pushing events as below:

class ParentActor extends Actor {
  ...

    override def preStart(): Unit = {
    super.preStart()

    // Observable to stream events regarding PowerPlant's
    val powerPlantEventObservable =
    // For every config.database.refreshInterval in seconds
      Observable.interval(config.database.refreshInterval)
        // We ask the actor for the latest messages
        .map(_ => (dbServiceActor ? DBServiceActor.PowerPlantEvents).mapTo[PowerPlantEventsSeq])
        .concatMap(Observable.fromFuture(_))
        .concatMap(Observable.fromIterable(_))

    // Subscriber that pipes the messages to this Actor
    cancelable := powerPlantEventObservable.subscribe { update =>
      (self ? update).map(_ => Continue)
    }
  }
}

So what happens above is that, I'm asking another Actor called DBServiceActor for a List of events and when these events are available, I'm piping it to the ParentActor (self ? update). The receive method of the ParentActor looks like this and this is where I want to restart my child actor . asynchronously:

    override def receive: Receive = {

        case PowerPlantUpdateEvent(id, powerPlantCfg) =>
          log.info(s"Re-starting PowerPlant actor with id = $id and type ${powerPlantCfg.powerPlantType}")

          // I want to stop the actor first by finding it from the actor system
          // If it exists, do a context.stop on the Actor instance
          // Once it is stopped, I want to start it again by creating a new instance of this Actor
          // Once this new Actor instance is created, I want to signal my Monix Observer to send me the next event
      }

Any suggestions?

[Akka Team]

Hi Joe,

Watching the child actor before stopping it will give you a Terminated message which will let you know that the child terminated, so that you can start a new one. If the id and powerPlantCfg is needed when starting anew you can put that in the actor state, as a map for keyed by the child ActorRef for example, so that you can look it up when the Terminated message arrives.

--

Johan

Akka Team

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