将简单的Scala远程参与者示例移植到Akka参与者

Question

我尝试移植从Scala角色向Akka角色发送"Ping“和"Pong”的this simple actor example，但我一直收到错误，我想知道这只是一个简单的错误还是一些根本的错误。

考虑下面的代码：

import akka.actor.Actor._
import akka.actor.Actor

case class Message(text: String)

class PingPongActor(name: String) extends Actor {

  def receive = {
      case Message(msg) =>
        println("received: " + msg)
        Thread.sleep(1000)
        self.reply(Message("Ping"))
      case None => println("ping: timed out!")
  }
}

object Ping extends App {
  remote.start("localhost", 2552)
        .register("ping-service", actorOf(new PingPongActor("pong")))

  val actor = remote.actorFor("ping-service", "localhost", 2552)

  actor ! (Message("Ping"))
}

object Pong extends App {
  remote.start("localhost", 2553)
        .register("pong-service", actorOf(new PingPongActor("ping")))

  val actor = remote.actorFor("pong-service", "localhost", 2553)

  actor ! (Message("Pong"))
}

我一直收到这个错误：

received: Ping
[GENERIC] [07.10.11 23:18] [RemoteServerStarted(akka.remote.netty.NettyRemoteSupport@3ff2cea2)]
[ERROR]   [07.10.11 23:18] [akka:event-driven:dispatcher:global-2] [LocalActorRef] 
   No sender in scope, can't reply.
   You have probably:
      1. Sent a message to an Actor from an instance that is NOT an Actor.
      2. Invoked a method on an TypedActor from an instance NOT an TypedActor.
   You may want to have a look at safe_! for a variant returning a Boolean
akka.actor.IllegalActorStateException: 
   No sender in scope, can't reply.
   You have probably:
      1. Sent a message to an Actor from an instance that is NOT an Actor.
      2. Invoked a method on an TypedActor from an instance NOT an TypedActor.
   You may want to have a look at safe_! for a variant returning a Boolean
[laptop_e3263500-f129-11e0-a78d-001636ff8076]
    at akka.actor.NullChannel$.$bang(Channel.scala:177)
    at akka.actor.ActorRef$class.reply(ActorRef.scala:398)
    at akka.actor.LocalActorRef.reply(ActorRef.scala:605)
    at PingPongActor$$anonfun$receive$1.apply(RemoteActor.scala:21)
    at PingPongActor$$anonfun$receive$1.apply(RemoteActor.scala:15)
    at akka.actor.Actor$class.apply(Actor.scala:545)
    at PingPongActor.apply(RemoteActor.scala:13)

我的想法是启动两个应用程序，Ping和Pong，这两个应用程序尝试每秒发送一条消息并在终端上打印(如果两秒钟内没有收到消息，则打印一条错误消息)。

Answer 1

您的代码最大的基本问题是，您从参与者外部发送消息，因此响应无处可去。您会注意到，在原始示例中，初始Message("ping")是从Ping执行元的act()循环中发送的。但实际上你有几个问题，最好从头开始，稍微重组一下代码。下面是一个有效的示例，但它依赖于以特定的顺序启动客户端。当然，您可以重写此代码，以保持从PingActor重试连接。

sealed trait Message
case class Ping extends Message
case class Pong extends Message

class PingActor extends Actor {

  override def preStart = {
    val pong = remote.actorFor("pong-service", "localhost", 2553)
    pong ! Ping
  }

  def receive = {
    case Pong => {
      println("Received pong")
      Thread.sleep(1000)
      self.reply(Ping)
    }
  }
}

class PongActor extends Actor {
  def receive = {
    case Ping => {
      println("Received ping")
      Thread.sleep(1000)
      self.reply(Pong)
    }
  }
}

object pingApp extends App {
  val actor = actorOf(new PingActor)
  remote.start("localhost", 2552)
        .register("ping-service", actor)
}

object pongApp extends App {
  val actor = actorOf(new PongActor)
  remote.start("localhost", 2553)
        .register("pong-service", actor)
}