akka远程处理中的死信(scala)

Question

当我试图在我的本地主机上使用远程akka角色运行一个简单的示例时，我遇到了死信。

这是我的远程项目的build.sbt文件。

name := "HelloRemote"

version := "1.0"

scalaVersion := "2.11.2"

resolvers += "Typesafe Repository" at "http://repo.typesafe.com/typesafe/releases/"

libraryDependencies ++= Seq(
  "com.typesafe.akka" %% "akka-actor" % "2.3.6",
  "com.typesafe.akka" %% "akka-remote" % "2.3.6"
)

这是我用于远程系统的application.conf文件。

akka {
  actor {
    provider = "akka.remote.RemoteActorRefProvider"
   }
   remote {
     enabled-transports = ["akka.remote.netty.tcp"]
     netty.tcp {
       hostname = "127.0.0.1"
       port = 5100
     }
   }
}

这是我的远程系统的HelloRemote.scala文件。

package remote

import akka.actor._

object HelloRemote extends App  {
  val system = ActorSystem("HelloRemoteSystem")
  val remoteActor = system.actorOf(Props[RemoteActor], name = "RemoteActor")
  remoteActor ! "The RemoteActor is alive"
}

class RemoteActor extends Actor {
  def receive = {
    case msg: String =>
        println(s"RemoteActor received message '$msg'")
        sender ! "Hello from the RemoteActor"
  }
}

对于我的本地系统，build.sbt文件如下所示。

name := "HelloLocal"

version := "1.0"

scalaVersion := "2.11.2"

resolvers += "Typesafe Repository" at "http://repo.typesafe.com/typesafe/releases/"

libraryDependencies ++= Seq(
  "com.typesafe.akka" %% "akka-actor" % "2.3.6",
  "com.typesafe.akka" %% "akka-remote" % "2.3.6"
)

我的本地系统的application.conf文件是

akka {
  actor {
    provider = "akka.remote.RemoteActorRefProvider"
  }
  remote {
    enabled-transports = ["akka.remote.netty.tcp"]
    netty.tcp {
      hostname = "127.0.0.1"
      port = 0
    }
  }
}

我的本地系统的HelloLocal.scala文件是

package local

import akka.actor._

object Local extends App {

  val system = ActorSystem("LocalSystem")
  val localActor = system.actorOf(Props[LocalActor], name = "LocalActor")  // the local actor
  localActor ! "START"                                                     // start the action

}

class LocalActor extends Actor {

  // create the remote actor
  val remote = context.actorSelection("akka.tcp://HelloRemoteSystem@127.0.0.1:5100/user/RemoteActor")
  var counter = 0

  def receive = {
    case "START" =>
        remote ! "Hello from the LocalActor"
    case msg: String =>
        println(s"LocalActor received message: '$msg'")
        if (counter < 5) {
            sender ! "Hello back to you"
            counter += 1
        }
  }
}

当我第一次运行HelloRemote.scala时，The RemoteActor is alive按照预期打印出来，然后立即得到错误信息

[INFO] [09/16/2014 10:52:47.585] [HelloRemoteSystem-akka.actor.default-dispatche
r-4] [akka://HelloRemoteSystem/deadLetters] Message [java.lang.String] from Acto
r[akka://HelloRemoteSystem/user/RemoteActor#1051175275] to Actor[akka://HelloRem
oteSystem/deadLetters] was not delivered. [1] dead letters encountered. This log
ging can be turned off or adjusted with configuration settings 'akka.log-dead-le
tters' and 'akka.log-dead-letters-during-shutdown'.

当我运行本地系统HelloLocal.scala时，我得到了一个类似的错误，然后什么也没有发生。我是不是做错了什么？

Answer 1

当您从参与者外部发送消息时，Akka会以发送者的身份填写死信邮箱。当HelloRemote.scala中的RemoteActor回复时，它是在回复死信邮箱，因为它收到的消息是从参与者外部发送的。

目前，HelloRemote.scala甚至不涉及远程处理，因为您只部署了一个本地参与者。

当您运行HelloLocal.scala时，我怀疑您的HelloRemote参与者系统正在终止，因为没有任何东西可以让它继续运行。

Answer 2

我以前也遇到过同样的问题，我使用val config = ConfigFactory.parsingString("---Configuration---")而不是配置文件解决了这个问题。希望它能为你工作。

Answer 3

我在做同样的例子时也遇到了这个问题。我遗漏的部分是将application.conf放在src/main/resources目录中。

如果在启动服务器时它位于正确的位置，您应该会看到这样的信息消息：

[INFO] [03/02/2016 19:06:10.365] [main] [akka.remote.Remoting] Starting remoting
[INFO] [03/02/2016 19:06:10.497] [main] [akka.remote.Remoting] Remoting started; listening on addresses : akka.tcp://HelloRemoteSystem@127.0.0.1:5100]
[INFO] [03/02/2016 19:06:10.499] [main] [akka.remote.Remoting] Remoting now listens on addresses: [akka.tcp://HelloRemoteSystem@127.0.0.1:5100]

我使用的blog post的目录结构如下：

HelloRemote/
|-- build.sbt
|-- src
    |-- main
    │   |-- java
    │   |-- resources
    │   │   +-- application.conf <--------------------------
    │   +-- scala
    │       +-- remote
    │           +-- HelloRemote.scala
    +-- test
        |-- java
        |-- resources
        +-- scala

正如Ryan已经提到的，死信错误是字符串消息"The RemoteActor is alive“不是参与者的副作用，因此它不能接收回消息"Hello from the RemoteActor”。这是示例中的一个小错误，但不会导致远程参与者和本地参与者无法相互交谈的失败。