处理Akka演员中的错误 [英] Handling Faults in Akka actors

问题描述

我有一个非常简单的示例，其中有一个Actor（ SimpleActor ）通过向自身发送消息来执行定期任务。该消息已在参与者的构造函数中安排。在正常情况下（即无故障），一切正常。

I've a very simple example where I've an Actor (SimpleActor) that perform a periodic task by sending a message to itself. The message is scheduled in the constructor for the actor. In the normal case (i.e., without faults) everything works fine.

但是，如果Actor必须处理错误，该怎么办。我有另一个演员（ SimpleActorWithFault ）。这个演员可能有毛病。在这种情况下，我通过抛出异常来生成自己。发生故障时（即 SimpleActorWithFault 引发异常），它将自动重新启动。但是，此重新启动使Actor内部的调度程序混乱，该调度程序不再具有例外功能。而且，如果故障发生得足够快，它将产生更多的意外行为。

But what if the Actor has to deal with faults. I've another Actor (SimpleActorWithFault). This actor could have faults. In this case, I'm generating one myself by throwing an exception. When a fault happens (i.e., SimpleActorWithFault throws an exception) it is automatically restarted. However, this restart messes up the scheduler inside the Actor which no longer functions as excepted. And if the faults happens rapidly enough it generates more unexpected behavior.

我的问题是在这种情况下处理错误的首选方法是什么？我知道我可以使用 Try 块来处理异常。但是，如果我要扩展另一个演员，使我无法在超类中进行尝试，或者在某些情况下出现例外故障，该演员会发生这种情况。

My question is what's the preferred way to dealing with faults in such cases? I know I can use Try blocks to handle exceptions. But what if I'm extending another actor where I cannot put a Try in the super class or some case when I'm an excepted fault happens in the actor.

import akka.actor.{Props, ActorLogging}
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.duration._
import akka.actor.Actor

case object MessageA

case object MessageToSelf


class SimpleActor extends Actor with ActorLogging {

  //schedule a message to self every second
  context.system.scheduler.schedule(0 seconds, 1 seconds, self, MessageToSelf)

  //keeps track of some internal state
  var count: Int = 0

  def receive: Receive = {
    case MessageA => {
      log.info("[SimpleActor] Got MessageA at %d".format(count))
    }
    case MessageToSelf => {
      //update state and tell the world about its current state 
      count = count + 1
      log.info("[SimpleActor] Got scheduled message at %d".format(count))

    }
  }

}


class SimpleActorWithFault extends Actor with ActorLogging {

  //schedule a message to self every second
  context.system.scheduler.schedule(0 seconds, 1 seconds, self, MessageToSelf)

  var count: Int = 0

  def receive: Receive = {
    case MessageA => {
      log.info("[SimpleActorWithFault] Got MessageA at %d".format(count))
    }
    case MessageToSelf => {
      count = count + 1
      log.info("[SimpleActorWithFault] Got scheduled message at %d".format(count))

      //at some point generate a fault
      if (count > 5) {
        log.info("[SimpleActorWithFault] Going to throw an exception now %d".format(count))
        throw new Exception("Excepttttttiooooooon")
      }
    }
  }

}


object MainApp extends App {
  implicit val akkaSystem = akka.actor.ActorSystem()
  //Run the Actor without any faults or exceptions 
  akkaSystem.actorOf(Props(classOf[SimpleActor]))

  //comment the above line and uncomment the following to run the actor with faults  
  //akkaSystem.actorOf(Props(classOf[SimpleActorWithFault]))

}

推荐答案

为避免弄乱调度程序，

class SimpleActor extends Actor with ActorLogging {

  private var cancellable: Option[Cancellable] = None

  override def preStart() = {
    //schedule a message to self every second
    cancellable = Option(context.system.scheduler.schedule(0 seconds, 1 seconds, self, MessageToSelf))
  }

  override def postStop() = {
    cancellable.foreach(_.cancel())
    cancellable = None
  }
...

正确处理异常（ akka.actor.Status.Failure用于在发件人使用询问模式的情况下正确回答询问）：

To correctly handle exceptions (akka.actor.Status.Failure is for correct answer to an ask in case of Ask pattern usage by sender):

...
def receive: Receive = {
    case MessageA => {
      try {
        log.info("[SimpleActor] Got MessageA at %d".format(count))
      } catch {
        case e: Exception =>
          sender ! akka.actor.Status.Failure(e)
          log.error(e.getMessage, e)
      }
    }
...

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