In Akka, how do I know when an actor is ready to use after having been registered with actorOf()?

Question

If I create an actor using context().actorOf() in Akka, I get back a valid ActorRef. However, if I do the same but create an ActorRef using actorFor and the path I know that the actor will appear at, I do not reliably get a valid ActorRef back. How can I tell that an actor has been registered successfully?

In the description above, I could simply use the ActorRef returned from actorOf(). However, in my actual case I create an actor that itself registers a child actor and I need to resolve that, so the problem in general is "how can I wait / register to be informed of an actor having been registered at a known path?".

Answer 1

Since Akka 2.2.1 you can use ActorSelection.resolveOne to get an ActorRef from an actor selection:

implicit val timeout = Timeout(5, TimeUnit.SECONDS)
val selection = system.actorSelection("/user/myActor")
val actor = Await.result(selection.resolveOne(), timeout.duration)

From the docs http://doc.akka.io/api/akka/2.2.1/index.html#akka.actor.ActorSelection

Resolve the ActorRef matching this selection. The result is returned as a Future that is completed with the ActorRef if such an actor exists. It is completed with failure ActorNotFound if no such actor exists or the identification didn't complete within the supplied timeout.

Under the hood it talks to the actor to verify its existence and acquire its ActorRef.