Package akka.actor

Class ActorRef

  • All Implemented Interfaces:
    java.io.Serializable, java.lang.Comparable<ActorRef>, scala.Serializable
    Direct Known Subclasses:
    InternalActorRef

    public abstract class ActorRef
    extends java.lang.Object
    implements java.lang.Comparable<ActorRef>, scala.Serializable
    Immutable and serializable handle to an actor, which may or may not reside on the local host or inside the same ActorSystem. An ActorRef can be obtained from an ActorRefFactory, an interface which is implemented by ActorSystem and 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 akka.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 akka.pattern.Patterns.ask;
     import static akka.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 ActorRefFactory.stop(ref), or send a 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:
    Serialized Form
    • Constructor Detail

      • ActorRef

        public ActorRef()
    • Method Detail

      • path

        public abstract ActorPath path()
        Returns the path for this actor (from this actor up to the root actor).
        Returns:
        (undocumented)
      • 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 java.lang.Comparable<ActorRef>
        Parameters:
        other - (undocumented)
        Returns:
        (undocumented)
      • tell

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

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

        Parameters:
        msg - (undocumented)
        sender - (undocumented)
      • forward

        public void forward​(java.lang.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/'?'.

        Parameters:
        message - (undocumented)
        context - (undocumented)
      • isTerminated

        public abstract boolean isTerminated()
        Deprecated.
        Use context.watch(actor) and receive Terminated(actor). Since 2.2.
        INTERNAL API Is the actor shut down? The contract is that if this method returns true, then it will never be false again. But you cannot rely on that it is alive if it returns false, since this by nature is a racy method.
        Returns:
        (undocumented)
      • hashCode

        public final int hashCode()
        Overrides:
        hashCode in class java.lang.Object
      • equals

        public final boolean equals​(java.lang.Object that)
        Equals takes path and the unique id of the actor cell into account.
        Overrides:
        equals in class java.lang.Object
        Parameters:
        that - (undocumented)
        Returns:
        (undocumented)
      • toString

        public java.lang.String toString()
        Overrides:
        toString in class java.lang.Object