code: package io.ray.runtime.actor;
  
  import io.ray.api.ActorHandle;
  import io.ray.api.id.ActorId;
  import io.ray.api.id.ObjectId;
  import java.io.Externalizable;
  import java.io.IOException;
  import java.io.ObjectInput;
  import java.io.ObjectOutput;
  import java.util.concurrent.atomic.AtomicReference;
  
  /** Implementation of actor handle for local mode. */
  public class LocalModeActorHandle implements ActorHandle, Externalizable {
  
    private ActorId actorId;
  
    private AtomicReference<ObjectId> previousActorTaskDummyObjectId = new AtomicReference<>();
  
    public LocalModeActorHandle(ActorId actorId, ObjectId previousActorTaskDummyObjectId) {
      this.actorId = actorId;
      this.previousActorTaskDummyObjectId.set(previousActorTaskDummyObjectId);
    }
  
    /** Required by FST. */
    public LocalModeActorHandle() {}
  
    @Override
    public ActorId getId() {
      return actorId;
    }
  
    public ObjectId exchangePreviousActorTaskDummyObjectId(ObjectId previousActorTaskDummyObjectId) {
      return this.previousActorTaskDummyObjectId.getAndSet(previousActorTaskDummyObjectId);
    }
  
    public LocalModeActorHandle copy() {
      return new LocalModeActorHandle(this.actorId, this.previousActorTaskDummyObjectId.get());
    }
  
    @Override
    public synchronized void writeExternal(ObjectOutput out) throws IOException {
      out.writeObject(actorId);
      out.writeObject(previousActorTaskDummyObjectId.get());
    }
  
    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
      actorId = (ActorId) in.readObject();
      previousActorTaskDummyObjectId.set((ObjectId) in.readObject());
    }
  }
  