由 BackoffSupervisor 监督的 Actor 在重启后丢失隐藏的消息

Question

我有一个 stash 使用的演员。有时，当它崩溃时，它会丢失所有隐藏的消息。我发现这取决于我使用什么监督逻辑。

我写了一个简单的例子。

藏匿的演员：

case object WrongMessage
case object TestMessage
case object InitialMessage

class TestActor extends Actor with Stash {
  override def receive: Receive = uninitializedReceive

  def uninitializedReceive: Receive = {
    case TestMessage =>
      println(s"stash test message")
      stash()

    case WrongMessage =>
      println(s"wrong message")
      throw new Throwable("wrong message")

    case InitialMessage =>
      println(s"initial message")
      context.become(initializedReceive)
      unstashAll()
  }

  def initializedReceive: Receive = {
    case TestMessage =>
      println(s"test message")
  }
}

在下面的代码中，TestActor never 收到隐藏的 TestMessage:

object Test1 extends App {
  implicit val system: ActorSystem = ActorSystem()
  val actorRef = system.actorOf(BackoffSupervisor.props(Backoff.onFailure(
      Props[TestActor], "TestActor", 1 seconds, 1 seconds, 0
  ).withSupervisorStrategy(OneForOneStrategy()({
    case _ => SupervisorStrategy.Restart
  }))))
  actorRef ! TestMessage
  Thread.sleep(5000L)
  actorRef ! WrongMessage
  Thread.sleep(5000L)
  actorRef ! InitialMessage
}

但是这段代码运行良好：

class SupervisionActor extends Actor {
  val testActorRef: ActorRef = context.actorOf(Props[TestActor])

  override def supervisorStrategy: SupervisorStrategy = OneForOneStrategy()({
    case _ => SupervisorStrategy.Restart
  })

  override def receive: Receive = {
    case message => testActorRef forward message
  }
}

object Test2 extends App {
  implicit val system: ActorSystem = ActorSystem()
  val actorRef = system.actorOf(Props(classOf[SupervisionActor]))
  actorRef ! TestMessage
  Thread.sleep(5000L)
  actorRef ! WrongMessage
  Thread.sleep(5000L)
  actorRef ! InitialMessage
}

我调查了资料，发现演员监督使用 LocalActorRef.restart method which backed by system dispatcher logic, but BackoffSupervisor simply creates a new actor after termination of the old one。有什么办法可以解决这个问题吗？

Answer 1

我不确定是否可以在 BackoffSupervisor 下使 restart 正确发送隐藏消息而无需一些自定义重新实现工作。

正如您已经指出的，BackoffSupervisor 有自己的 restart 绕过标准 actor 生命周期。事实上，BackoffOnRestartSupervisor 源代码中明确指出：

Whatever the final Directive is, we will translate all Restarts to our own Restarts, which involves stopping the child.

如果你还没有读过这篇文章reported issue, it has a relevant discussion re: problem with Backoff.onFailure。

Backoff.onStop 也会提供想要的 BackoffSupervisor 功能，但不幸的是它有自己的用例，不会被异常触发。

由 BackoffSupervisor 监督的 Actor 在重启后丢失隐藏的消息

Actor supervised by BackoffSupervisor loses stashed messages after restart

scala

actor

akka

akka-supervision