akka：未收到终止回调

Question

我有一个 actorsystem，我在其中注册了一些关于 actorsystem 终止的代码。代码如下-

object ChildActor {
  class Msg
}

class ChildActor extends Actor {
  val log = Logging(context.system, this)

  override def receive: Receive = {
    case a : String => log.info(s"received $a")
    case _ : Msg => throw new OutOfMemoryError("error")
  }
}

class ParentActor extends Actor {
  override val supervisorStrategy = OneForOneStrategy() {
    case _: OutOfMemoryError => {
      Stop
    }
    case _: Exception => Stop
  }
  val child = context.actorOf(Props[ChildActor], "child")
  override def receive: Receive = {
    case a: String => child ! a
    case msg : Msg => child ! msg
  }
}

object Test extends App {

  val customConf = ConfigFactory.parseString("""
  akka {
    jvm-exit-on-fatal-error = false
  }
  """)


  val actorSystem = ActorSystem("OOMException", ConfigFactory.load(customConf))

  actorSystem.registerOnTermination(println("going off"))

  val actor = actorSystem.actorOf(Props[ParentActor], "parentActor")

  actor ! new Msg

}

我注意到的奇怪行为是我的回调。当我正常运行应用程序时，我永远不会收到我注册代码的回调。

但是，当我在调试模式下运行并在 terminate() 方法中等待几秒钟时，该行会被打印出来。我不确定为什么这几秒钟的等待是为了确保所有注册的回调都被触发，而在正常运行模式下它没有发生..有人知道吗？？

P.S : 我知道 OOM 是致命的，但我只是对手头的问题感到好奇，OOM 只是一种情况。

当我在最后进行线程转储时，我看到始终存在以下两个线程 -

"OOMException-akka.actor.default-dispatcher-2" #12 prio=5 os_prio=0 tid=0x000000001e8dd800 nid=0x1029c waiting on condition [0x0000000020eff000]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x0000000770700c90> (a akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinPool)
    at akka.dispatch.forkjoin.ForkJoinPool.scan(ForkJoinPool.java:2075)
    at akka.dispatch.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
    at akka.dispatch.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)

"OOMException-scheduler-1" #11 prio=5 os_prio=0 tid=0x000000001e5d8800 nid=0xfba4 waiting on condition [0x000000001f35e000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
    at java.lang.Thread.sleep(Native Method)
    at akka.actor.LightArrayRevolverScheduler.waitNanos(LightArrayRevolverScheduler.scala:85)
    at akka.actor.LightArrayRevolverScheduler$$anon$4.nextTick(LightArrayRevolverScheduler.scala:265)
    at akka.actor.LightArrayRevolverScheduler$$anon$4.run(LightArrayRevolverScheduler.scala:235)
    at java.lang.Thread.run(Thread.java:748)

调度程序应该已经完成​​，因为actor系统终止了..不确定为什么它处于定时等待状态..

Answer 1

App 在这里可能很棘手，可能在执行回调之前 JVM 已终止（因为剩下的所有线程都是守护线程）。

我首先建议将您的应用代码放入 def main(...) 方法中。

使用类似这样的东西而不是println:

val promise = Promise.empty[Unit]
actorSystem.registerOnTermination(promise.success(()))
val actor = actorSystem.actorOf(Props[ParentActor], "parentActor")
actor ! new Msg
Await.ready(promise.future, Duration.INF)
println("going off")