我如何获得演员系统中的所有演员

Question

I have a actor system. I would like to log (for testing) all the actors (addresses/paths) in the system

I tried calling

ActorSelection actorSelection = context().actorSelection("akka://*");
System.out.println(Arrays.asList(actorSelection.path()));

inside one of the root actors. It prints

[akka:, ^\Q\E.*\Q\E$]

But for fact I know there are more actors in my system and working. Whats the proper way to get this list?

Answer 1

If it's for test purposes, I would create a dedicated RetrieveActors actor with this behavior (akka v2.4.17 syntax):

import akka.actor.*;
import akka.event.Logging;
import akka.event.LoggingAdapter;

public class RetrieveActors extends UntypedActor {
    private LoggingAdapter log = Logging.getLogger(getContext().system(), this);
    private String identifyId;

       public RetrieveActors(String identifyId) {
           this.identifyId = identifyId;
       }

       @Override
       public void preStart() {
           ActorSelection selection = getContext().actorSelection("/*");
           selection.tell(new Identify(identifyId), getSelf());
       }

       @Override
       public void onReceive(Object message) throws Throwable {
           if (message instanceof ActorIdentity) {
               ActorIdentity identity = (ActorIdentity) message;

               if (identity.correlationId().equals(identifyId)) {
                   ActorRef ref = identity.getRef();

                   if (ref != null) { // to avoid NullPointerExceptions
                       // Log or store the identity of the actor who replied
                       log.info("The actor " + ref.path().toString() + " exists and has replied!");

                       // We want to discover all children of the received actor (recursive traversal)
                       ActorSelection selection = getContext().actorSelection(ref.path().toString() + "/*");
                       selection.tell(new Identify(identifyId), getSelf());
                   }

               }

           }
       }
}

And then when you want to list all your actors created, just create a new instance of RetrieveActors :

// "1" is the identifyId to make your retrieval calls unique to this actor instance
system.actorOf(Props.create(RetrieveActors.class, "1"), "LookupActor1");

Note that some actors may be quite long to answer if they are busy since this pattern use normal messages and mailboxes. Also, the delivery may be not guaranteed. You will retrieve only the actors that have been already created. More info here .

If you need to get several times all actors in your akka system, I suggest you to modify the RetrieveActors behavior to perform actor retrieval in reaction of some custom message instead of doing it at initialization. This may avoid you to create several instances of the same Actor.

Hope it helps.

Answer 2

ActorSystem has opened printTree method, so use something similar to

   ActorSystem<Object> actors = ActorSystem.create(...);
   System.out.println(actors.printTree());