Package org.apache.pekko.actor

Class ActorRef

java.lang.Object
org.apache.pekko.actor.ActorRef
All Implemented Interfaces:
Serializable, Comparable<ActorRef>
Direct Known Subclasses:
Nobody$
public abstract class ActorRef extends Object implements Comparable<ActorRef>, Serializable
Immutable and serializable handle to an actor, which may or may not reside on the local host or inside the same pekko.actor.ActorSystem. An ActorRef can be obtained from an pekko.actor.ActorRefFactory, an interface which is implemented by ActorSystem and pekko.actor.ActorContext. This means actors can be created top-level in the ActorSystem or as children of an existing actor, but only from within that actor.

ActorRefs can be freely shared among actors by message passing. Message passing conversely is their only purpose, as demonstrated in the following examples:

Scala: 


 import org.apache.pekko.pattern.ask
 import scala.concurrent.Await

 class ExampleActor extends Actor {
   val other = context.actorOf(Props[OtherActor], "childName") // will be destroyed and re-created upon restart by default

   def receive {
     case Request1(msg) => other ! refine(msg)     // uses this actor as sender reference, reply goes to us
     case Request2(msg) => other.tell(msg, sender()) // forward sender reference, enabling direct reply
     case Request3(msg) =>
       implicit val timeout = Timeout(5.seconds)
       (other ? msg) pipeTo sender()
       // the ask call will get a future from other's reply
       // when the future is complete, send its value to the original sender
   }
 }

Java: 


 import static org.apache.pekko.pattern.Patterns.ask;
 import static org.apache.pekko.pattern.Patterns.pipe;

 public class ExampleActor extends AbstractActor {
   // this child will be destroyed and re-created upon restart by default
   final ActorRef other = getContext().actorOf(Props.create(OtherActor.class), "childName");
   @Override
   public Receive createReceive() {
     return receiveBuilder()
       .match(Request1.class, msg ->
         // uses this actor as sender reference, reply goes to us
         other.tell(msg, getSelf()))
       .match(Request2.class, msg ->
         // forward sender reference, enabling direct reply
         other.tell(msg, getSender()))
       .match(Request3.class, msg ->
         // the ask call will get a future from other's reply
         // when the future is complete, send its value to the original sender
         pipe(ask(other, msg, 5000), context().dispatcher()).to(getSender()))
       .build();
   }
 }

ActorRef does not have a method for terminating the actor it points to, use pekko.actor.ActorRefFactory.stop(ref), or send a pekko.actor.PoisonPill, for this purpose.

Two actor references are compared equal when they have the same path and point to the same actor incarnation. A reference pointing to a terminated actor doesn't compare equal to a reference pointing to another (re-created) actor with the same path.

If you need to keep track of actor references in a collection and do not care about the exact actor incarnation you can use the ActorPath as key because the unique id of the actor is not taken into account when comparing actor paths.

See Also:

  • Constructor Details

    • ActorRef

      public ActorRef()

  • Method Details

    • noSender

      public static final ActorRef noSender()
      Use this value as an argument to tell(java.lang.Object, org.apache.pekko.actor.ActorRef) if there is not actor to reply to (e.g. when sending from non-actor code).

    • path

      public abstract ActorPath path()
      Returns the path for this actor (from this actor up to the root actor).

    • compareTo

      public final int compareTo(ActorRef other)
      Comparison takes path and the unique id of the actor cell into account.
      Specified by:
      compareTo in interface Comparable<ActorRef>

    • tell

      public final void tell(Object msg, ActorRef sender)
      Sends the specified message to this ActorRef, i.e. fire-and-forget semantics, including the sender reference if possible.

      Pass pekko.actor.ActorRef noSender or null as sender if there is nobody to reply to

    • $bang

      public abstract void $bang(Object message, ActorRef sender)
      Scala API: Sends a one-way asynchronous message. E.g. fire-and-forget semantics.

      If invoked from within an actor then the actor reference is implicitly passed on as the implicit 'sender' argument.

      This actor 'sender' reference is then available in the receiving actor in the 'sender()' member variable, if invoked from within an Actor. If not then no sender is available. 

         actor ! message

    • forward

      public void forward(Object message, ActorContext context)
      Forwards the message and passes the original sender actor as the sender.

      Works, no matter whether originally sent with tell/'!' or ask/'?'.

    • hashCode

      public final int hashCode()
      Overrides:
      hashCode in class Object

    • equals

      public final boolean equals(Object that)
      Equals takes path and the unique id of the actor cell into account.
      Overrides:
      equals in class Object

    • toString

      public String toString()
      Overrides:
      toString in class Object

    • $bang$default$2

      public ActorRef $bang$default$2(Object message)