监控封闭图 Akka Stream

Question

如果我在 Akka Stream 中创建了RunningGraph，我怎么知道（从外部）

1. 何时所有节点因完成而被取消？
2. 所有节点何时因错误而停止？

Answer 1

我认为没有办法对任意图执行此操作，但如果您控制了您的图，您只需将监控接收器附加到每个可能失败或完成的节点的输出（这些是具有至少一个输出的节点），例如：

import akka.actor.Status

// obtain graph parts (this can be done inside the graph building as well)
val source: Source[Int, NotUsed] = ...
val flow: Flow[Int, String, NotUsed] = ...
val sink: Sink[String, NotUsed] = ...

// create monitoring actors
val aggregate = actorSystem.actorOf(Props[Aggregate])
val sourceMonitorActor = actorSystem.actorOf(Props(new Monitor("source", aggregate)))
val flowMonitorActor = actorSystem.actorOf(Props(new Monitor("flow", aggregate)))

// create the graph
val graph = GraphDSL.create() { implicit b =>
   import GraphDSL._

   val sourceMonitor = b.add(Sink.actorRef(sourceMonitorActor, Status.Success(()))),
   val flowMonitor = b.add(Sink.actorRef(flowMonitorActor, Status.Success(())))

   val bc1 = b.add(Broadcast[Int](2))
   val bc2 = b.add(Broadcast[String](2))

   // main flow
   source ~> bc1 ~> flow ~> bc2 ~> sink

   // monitoring branches
   bc1 ~> sourceMonitor
   bc2 ~> flowMonitor

   ClosedShape
}

// run the graph
RunnableGraph.fromGraph(graph).run()

class Monitor(name: String, aggregate: ActorRef) extends Actor {
  override def receive: Receive = {
    case Status.Success(_) => aggregate ! s"$name completed successfully"
    case Status.Failure(e) => aggregate ! s"$name completed with failure: ${e.getMessage}"
    case _ =>
  }
}

class Aggregate extends Actor {
  override def receive: Receive = {
    case s: String => println(s)
  }
}

也可以只创建一个监控参与者并在所有监控接收器中使用它，但在这种情况下，您将无法轻松区分失败的流。

还有一个关于源和流的watchTermination() 方法，它允许实现一个在此时与流一起终止的未来。我认为GraphDSL 可能很难使用，但使用常规流方法可能看起来像这样：

import akka.Done
import akka.actor.Status
import akka.pattern.pipe

val monitor = actorSystem.actorOf(Props[Monitor])
source
  .watchTermination()((f, _) => f pipeTo monitor) 
  .via(flow).watchTermination((f, _) => f pipeTo monitor)
  .to(sink)
  .run()

class Monitor extends Actor {
  override def receive: Receive = {
    case Done => println("stream completed")
    case Status.Failure(e) => println(s"stream failed: ${e.getMessage}")
  }
}

您可以在将未来的值传递给参与者以区分流之前对其进行转换。