How to wait actors stop in scala - scala

Question

class A extends Actor{
def act = {
//do something
}
}
val a = new A
a.join // How Can I implement it
I have read How can I join started Actor?
however I still don't know how to write the code.

Answer 1

The standard way to achieve this would be to use the Ask Pattern
It goes something like this:
class MyActor extends Actor {
def receive = {
case "Ping" => sender ! "Pong"
}
}
val future = actor ? "Ping"
val result = Await.result(future, 10 seconds) //blocks until the response has been received, or the timeout reached
This is assuming that you want to block on a message from the actor. If you want to tell when an actor has died, you need to use DeathWatch like this:
case object TellMeWhenActorDies
case object ActorDied
class Watcher extends Actor {
val child = context.actorOf(Props[Watched], "watched")
context.watch(child)
override def receive: Receive = {
case TellMeWhenActorDies => context.become(waitingForDeath(sender))
}
def waitingForDeath(client: ActorRef): Receive = {
case Terminated(name) => client ! ActorDied
}
}
class Watched extends Actor {
override def receive: Receive = {
case _ => //do nothing
}
}
val finishedFuture = supervisor ? TellMeWhenActorDies
system.actorSelection("/user/$a/watched").tell(PoisonPill, supervisor)
Await.result(finishedFuture, 10 seconds)

Answer 2

Simply use the gracefulStop pattern. This is example is directly from the Akka docs:
try {
val stopped: Future[Boolean] = gracefulStop(actorRef, 5 seconds, Manager.Shutdown)
Await.result(stopped, 6 seconds)
// the actor has been stopped
} catch {
// the actor wasn't stopped within 5 seconds
case e: akka.pattern.AskTimeoutException =>
}