Question

在一个简单的测试中，我期待流程生成并打印一秒钟的数字。我想测试处理背压的流操作，并且需要一个不支持背压的Source。

... with FreeSpec ... {

  implicit val system = ActorSystem(this.getClass.getSimpleName)
  private val matSettings: ActorMaterializerSettings =
ActorMaterializerSettings(system).withDebugLogging(true).withFuzzing(true)
  implicit val mat = ActorMaterializer(matSettings.withInputBuffer(1, 1))

"must print numbers for a second" in {

  val source: Source[Double, ActorRef] =
    Source.actorRef(100, OverflowStrategy.fail).map(_ => Random.nextDouble())

  val sink: Sink[Double, Future[Done]] = Sink.foreach(println)

  val actorRef: ActorRef = Flow[Double].to(sink).runWith(source)

  system.scheduler.schedule(0.micro, 1.milli, actorRef, "tick")(system.dispatcher)

  Thread.sleep(1000)
  println("done")
}

然而，演员似乎在流程实现后立即停止，没有一条消息被传递，只发送了两封。我在哪里误解了这里发生的事情，我如何得到预期的结果？日志：

08:24:07.077 DEBUG a.a.LocalActorRefProvider$SystemGuardian - now supervising Actor[akka://BuffersAndTicksSpec/system/UnhandledMessageForwarder#1836419858]
08:24:07.078 DEBUG akka.event.EventStream - subscribing Actor[akka://BuffersAndTicksSpec/system/UnhandledMessageForwarder#1836419858] to channel class akka.actor.UnhandledMessage
08:24:07.079 DEBUG akka.event.EventStream - Default Loggers started
08:24:07.079 DEBUG a.e.LoggingBus$$anonfun$startDefaultLoggers$2$$anon$3 - started (akka.event.LoggingBus$$anonfun$startDefaultLoggers$2$$anon$3@26bf15e8)
08:24:07.079 DEBUG akka.event.EventStream - unsubscribing StandardOutLogger from all channels
08:24:07.080 DEBUG a.a.LocalActorRefProvider$SystemGuardian - now supervising Actor[akka://BuffersAndTicksSpec/system/deadLetterListener#-876496689]
08:24:07.080 DEBUG akka.event.EventStream - subscribing Actor[akka://BuffersAndTicksSpec/system/deadLetterListener#-876496689] to channel class akka.actor.DeadLetter
08:24:07.080 DEBUG akka.event.DeadLetterListener - started (akka.event.DeadLetterListener@691f7305)
08:24:07.081 DEBUG a.a.LocalActorRefProvider$SystemGuardian - now supervising Actor[akka://BuffersAndTicksSpec/system/eventStreamUnsubscriber-1#722751434]
08:24:07.081 DEBUG akka.event.EventStreamUnsubscriber - registering unsubscriber with akka.event.EventStream@a27e5b9
08:24:07.081 DEBUG akka.event.EventStream - initialized unsubscriber to: Actor[akka://BuffersAndTicksSpec/system/eventStreamUnsubscriber-1#722751434], registering 3 initial subscribers with it
08:24:07.082 DEBUG akka.event.EventStreamUnsubscriber - started (akka.event.EventStreamUnsubscriber@75843fb6)
08:24:07.082 DEBUG akka.event.EventStreamUnsubscriber - watching Actor[akka://BuffersAndTicksSpec/system/log1-Slf4jLogger#28712451] in order to unsubscribe from EventStream when it terminates
08:24:07.082 DEBUG akka.event.EventStreamUnsubscriber - watching Actor[akka://BuffersAndTicksSpec/system/UnhandledMessageForwarder#1836419858] in order to unsubscribe from EventStream when it terminates
08:24:07.082 DEBUG akka.event.slf4j.Slf4jLogger - now watched by Actor[akka://BuffersAndTicksSpec/system/eventStreamUnsubscriber-1#722751434]
08:24:07.083 DEBUG a.e.LoggingBus$$anonfun$startDefaultLoggers$2$$anon$3 - now watched by Actor[akka://BuffersAndTicksSpec/system/eventStreamUnsubscriber-1#722751434]
08:24:07.083 DEBUG akka.event.EventStreamUnsubscriber - watching Actor[akka://BuffersAndTicksSpec/system/deadLetterListener#-876496689] in order to unsubscribe from EventStream when it terminates
08:24:07.083 DEBUG akka.event.DeadLetterListener - now watched by Actor[akka://BuffersAndTicksSpec/system/eventStreamUnsubscriber-1#722751434]
08:24:07.164 DEBUG a.a.LocalActorRefProvider$Guardian - now supervising Actor[akka://BuffersAndTicksSpec/user/StreamSupervisor-0#-544371192]
08:24:07.164 DEBUG akka.stream.impl.StreamSupervisor - started (akka.stream.impl.StreamSupervisor@6fd27b4e)
08:24:07.173 WARN  a.stream.impl.ActorMaterializerImpl - Fuzzing mode is enabled on this system. If you see this warning on your production system then set akka.stream.materializer.debug.fuzzing-mode to off.
08:24:07.270 DEBUG akka.stream.impl.StreamSupervisor - now supervising Actor[akka://BuffersAndTicksSpec/user/StreamSupervisor-0/flow-0-0-unknown-operation#478879902]
08:24:07.276 DEBUG a.s.i.fusing.ActorGraphInterpreter - started (akka.stream.impl.fusing.ActorGraphInterpreter@42111ea7)
08:24:07.276 DEBUG akka.stream.impl.StreamSupervisor - now supervising Actor[akka://BuffersAndTicksSpec/user/StreamSupervisor-0/flow-0-1-actorRefSource#1199332529]
08:24:07.283 DEBUG akka.stream.impl.ActorRefSourceActor - started (akka.stream.impl.ActorRefSourceActor@6dbd251e)
08:24:07.289 INFO  akka.actor.RepointableActorRef - Message [java.lang.String] from Actor[akka://BuffersAndTicksSpec/deadLetters] to Actor[akka://BuffersAndTicksSpec/user/StreamSupervisor-0/flow-0-1-actorRefSource#1199332529] was not delivered. [1] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
08:24:07.290 DEBUG akka.stream.impl.ActorRefSourceActor - stopped
08:24:07.291 DEBUG a.s.i.fusing.ActorGraphInterpreter - stopped
08:24:07.297 INFO  akka.actor.RepointableActorRef - Message [java.lang.String] from Actor[akka://BuffersAndTicksSpec/deadLetters] to Actor[akka://BuffersAndTicksSpec/user/StreamSupervisor-0/flow-0-1-actorRefSource#1199332529] was not delivered. [2] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
done

Answer 1

此处的问题与您Source.actorRef的类型有关。即使演员可以接收Any类型的消息，当你将其包裹在Source中时，你需要给它一个类型（以实现Akka Streams强类型）。

示例：

val source: Source[Int, ActorRef] = Source.actorRef[Int](100, OverflowStrategy.fail)

幕后发生的事情是，Source会尝试将每封传入的讯息投放到Int。

在您的情况下，Source.actorRef未显式输入，因此编译器会推断Nothing。（这是因为您正在连接map阶段，其中所有内容都变为Double）。所有传入的“刻度”消息都会转换为Nothing，从而导致ClassCastException。

解决方案是输入您的Source.actorRef阶段

val source: Source[Double, ActorRef] =
      Source.actorRef[String](100, OverflowStrategy.fail).map(_ => Random.nextDouble())

为什么流会立即停止以及如何防止它

1 个答案: