CODEWITHSUNDEEP
scalaakkaactor
ademartini
ademartini

Reputation: 1441

Akka Ensure Poison Pill is Consumed

I would like to get a future that completes when an Akka actor has handled the PoisonPill.

I have tried:

someRef ? PoisonPill

but this never completes. I think you can only use '!' and not '?'. Any ideas?

Upvotes: 3

Views: 1022

Answers (1)

ale64bit
ale64bit

Reputation: 6242

If what you want is to monitor the life-cycle of some child actor, you can simply watch that actor and handle the Terminated message accordingly to your logic. For example:

class MyActor extends Actor {

  import context._ // to avoid writing context everywhere

  val child = actorOf(Props(new ChildActor)) // ChildActor is the type of the actor you are monitoring, the child
  watch(child) // subscribe to the Terminated message of the child

  override def receive: Receive = {
    case "kill" ⇒ child ! PoisonPill // kill the child. You could also use context.stop(child)
    case Terminated(`child`) ⇒ println("child died") // handle the termination of the child. Use back-ticks to make child a stable identifier
    case _ ⇒ println("meh") // who cares
  }
}

Now, if you want an explicit Future, the first thing that pops in my mind is passing a Promise to the actor you want to watch, and override postStop to complete the promise. It would look like this:

class MyActor(p: Promise[Unit]) extends Actor { // receive the Promise to complete

  override def receive: Receive = {
    case _ ⇒ println("meh") // who cares
  }

  override def postStop(): Unit = { // after stopped
    p.tryComplete(Success(())) // complete the promise
  }
}

object Main {
  def main(args: Array[String]) {
    val system = ActorSystem("test")
    val p = Promise[Unit]()
    val f = p.future // get the future from the promise
    val a = system.actorOf(Props(new MyActor(p))) // send the promise to the actor you want to watch

    f onSuccess { // register a callback when the future completes
      case _ ⇒ println("actor died")
    }

    a ! "foo"
    a ! PoisonPill
  }
}

Hope it helped. Cheers!

Upvotes: 1

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