Akka：我怎樣才能在另一個（非孩子）演員中捕捉到一個演員的失敗？

Question

我有兩個演員：

處理系統中某些進程的ProcessManager （例如，用戶注冊，購買等）

通知程序 - 如果ProcessManager中發生了某些錯誤，則應通知用戶。 我需要捕獲ProcessManager actor的失敗（它失敗並因任何原因而停止，例如，因為ActorInitializationException或達到最大重啟時間並且進程管理器actor被停止）。

   class ProcessManager extends Actor {
      override def receive: Receive = {
        ...
      }
    }

    class Notifier extends Actor {
      override def receive: Receive = {
        PROCESS MANAGER ACTOR FAILED AND STOPPED =>
          // Here I need to catch failure of ProcessManager actor
          // (it was failed and stopped for what ever
          // reason, for example, because of ActorInitializationException
          // or max restart time reached and Process manager actor was stopped).
          //
          // Then do some stuff, for example, send message to the client via web socket.
      }
    }


    class MyController @Inject() (cc: ControllerComponents, actorSystem: ActorSystem)
      (implicit exec: ExecutionContext) extends AbstractController(cc)  {


      // I need to catch failure of processManager in this actor.
      val notifier = actorSystem.actorOf(Props(classOf[Notifier]))

      def registerUser = Action.async {         

          // Actor may be stopped because of ActorInitializationException here
          val processManager = actorSystem.actorOf(Props(classOf[ProcessManager]))
              ...

         // OR it may be stopped here for any reason.
         processManager ! "some message which will fail and stop pm actor"

         Future.successfull(Ok("Thanks."))   
       }
   }

如何在Notifier actor中捕獲ProcessManager actor的終止（因為失敗）？

編輯讓我解釋一下我的問題的背景。

我正在Play控制器中創建PM演員並將消息發送給它（Tell），我立即向用戶返回Ok響應。 PM actor創建另一個子actor，在創建過程中拋出ActorInitializationException。 我需要通知用戶（通過Web套接字，使用Notifier actor），出現問題。

Answer 1

當ProcessManager actor永久停止時，您可以使用DeathWatch注冊Notifier actor以接收Terminated消息。 Notifier將需要對DeathWatch的ProcessManager actor的DeathWatch ，並且一種方法是將對ProcessManager的引用作為消息發送（這是安全的，因為ActorRef是不可變的和可序列化的）。

class Notifier extends Actor {
  var processManager: Option[ActorRef] = None

  def receive: Receive = {
    case aRef: ActorRef =>
      if (processManager.isEmpty) {
        processManager = Some(aRef)
        context.watch(aRef) // register to "watch" the process manager
      }
    case Terminated =>
      // process manager was permanently stopped
    case ...
  }
}

object Demo extends App {
  val actorSystem = ActorSystem("my-actor-system")

  val notifier = actorSystem.actorOf(Props(classOf[Notifier]))
  val processManager = actorSystem.actorOf(Props(classOf[ProcessManager]))

  notifier ! processManager // send processManager's ref to the notifier
  ...
  processManager ! "some message which will fail and stop pm actor"
  ...
}

需要注意的是：在嘗試創建ProcessManager時拋出ActorInitializationException之前，可能無法執行DeathWatch注冊。

---

如果您需要在ProcessManager的子ProcessManager拋出異常時向Notifier發送消息，則在ProcessManager覆蓋Supervisor策略並將此消息作為策略的一部分發送。 就像是：

class ProcessManager extends Actor {
  import akka.actor.OneForOneStrategy
  import akka.actor.SupervisorStrategy._
  import scala.concurrent.duration._

  override val supervisorStrategy =
    OneForOneStrategy(maxNrOfRetries = 10, withinTimeRange = 1 minute) {
      case _: ActorInitializationException =>
        val notifier = context.actorSelection("/path/to/notifier")
        notifier ! CustomErrorMessage
        Stop
      case _: Exception => Escalate
   }

   def receive: Receive = {
     ...
   }
}