Question

考虑下面的代码示例（版本1）。这里父actor（ActorA）向子actor（ActorB）发送消息然后停止self。由于父母演员的自我停止，在高负荷下，儿童演员甚至在从邮箱挑选消息之前就死了，因此消息变成了“死信”。（参见下面的示例输出1）。

出于某种原因，我无法修改应用程序设计以删除父actor的自动停止。

版本1

import akka.actor.Actor
import akka.actor.OneForOneStrategy
import akka.actor.SupervisorStrategy.Stop
import akka.actor.Props
import akka.actor.ActorSystem

object AkkaTest extends App {

  val system = ActorSystem("AkkaTest")

  for (i <- 1 to 5) {
    system.actorOf(Props[ActorA]) ! i  
  }

}

class ActorA extends Actor {

  def receive = {
    case i: Int => { 
      context.actorOf(Props[ActorB]) ! i
      context.stop(self)
    }
  }

  override def postStop = println("ActorA - stopped")

}

class ActorB extends Actor {

  def receive = {
    case i: Int => {
      println("ActorB - processing msg - " + i)
    }
  }

  override def postStop = println("ActorB - stopped")

}

示例输出1

ActorB - processing msg - 2
ActorB - processing msg - 1
ActorB - stopped
ActorB - stopped
ActorB - stopped
ActorB - stopped
ActorB - processing msg - 3
ActorB - stopped
ActorA - stopped
ActorA - stopped
[INFO] [09/09/2014 08:26:56.101] [AkkaTest-akka.actor.default-dispatcher-6] [akka://AkkaTest/user/$e/$a] Message [java.lang.Integer] from Actor[akka://AkkaTest/user/$e#-289783076] to Actor[akka://AkkaTest/user/$e/$a#-86921027] was not delivered. [1] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
[INFO] [09/09/2014 08:26:56.101] [AkkaTest-akka.actor.default-dispatcher-3] [akka://AkkaTest/user/$d/$a] Message [java.lang.Integer] from Actor[akka://AkkaTest/user/$d#-1255514179] to Actor[akka://AkkaTest/user/$d/$a#402128903] was not delivered. [2] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
ActorA - stopped
ActorA - stopped
ActorA - stopped

现在考虑以下代码修改（版本2）。通过从儿童演员向父演员引入消息确认，然后在收到此确认后自动停止父演员，摆脱死信（参见示例输出2）。

第2版

import akka.actor.Actor
import akka.actor.OneForOneStrategy
import akka.actor.SupervisorStrategy.Stop
import akka.actor.Props
import akka.actor.ActorSystem

object AkkaTest extends App {

  val system = ActorSystem("AkkaTest")

  for (i <- 1 to 5) {
    system.actorOf(Props[ActorA]) ! i  
  }

}

class ActorA extends Actor {

  def receive = {
    case i: Int => context.actorOf(Props[ActorB]) ! i
    case m: MsgAck => context.stop(self) 
  }

  override def postStop = println("ActorA - stopped")

}

class ActorB extends Actor {

  def receive = {
    case i: Int => {
      sender ! MsgAck()
      println("ActorB - processing msg - " + i)
    }
  }

  override def postStop = println("ActorB - stopped")

}

case class MsgAck()

样本输出2

ActorB - processing msg - 4
ActorB - processing msg - 2
ActorB - processing msg - 5
ActorB - processing msg - 3
ActorB - processing msg - 1
ActorB - stopped
ActorB - stopped
ActorB - stopped
ActorB - stopped
ActorB - stopped
ActorA - stopped
ActorA - stopped
ActorA - stopped
ActorA - stopped
ActorA - stopped

现在我的问题是，还有其他方法可以达到同样的目的吗？我的意思是摆脱死信。

Answer 1

当父母停止时，其所有孩子都将被停止。这导致死信。确保没有死信的唯一方法是确保父母活着，直到孩子收到消息。除了ack消息之外，我无法想到任何其他方式。

父母在发送消息后停止时，从父母演员到儿童演员的消息上的死信

1 个答案: