scala - 处理 Akka actor 中的错误

Question

我有一个非常简单的例子，我有一个 Actor ( SimpleActor )，它通过向自身发送消息来执行周期性任务。该消息在actor 的构造函数中被调度。在正常情况下(即没有故障)，一切正常。

但是如果 Actor 必须处理错误呢？我有另一个 Actor ( SimpleActorWithFault )。这个 Actor 可能有缺点。在这种情况下，我自己通过抛出异常来生成一个。当发生故障(即 SimpleActorWithFault 抛出异常)时，它会自动重新启动。但是，这种重新启动会弄乱 Actor 内的调度程序，该程序不再作为异常(exception)运行。如果故障发生得足够快，它会产生更多意想不到的行为。

我的问题是在这种情况下处理故障的首选方法是什么？ 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无法在父类(super class)中放置 Try 的角色，或者某些情况下我是 Actor 中发生的异常错误，该怎么办。

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]))

}

Answer 1

为了避免搞乱调度程序:

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 用于在发送者使用 Ask 模式的情况下正确回答问题):

...
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)
      }
    }
...