Question

下面是简化的代码段，其中GraphStateLogic实现作为构造函数参数传递给GraphStage：-

package akka.shapes.examples.notworking

import akka.actor.ActorSystem
import akka.stream._
import akka.stream.scaladsl.{GraphDSL, RunnableGraph, Sink, Source}
import akka.stream.stage.{GraphStage, GraphStageLogic, InHandler}

//This is base graph stage, where GraphStageLogic and SinkShape are passed in constructor parameter
class BaseGraphStage[T](val shape: SinkShape[T], graphStageLogic: GraphStageLogic) extends GraphStage[ SinkShape[T] ] {

  override def createLogic(inheritedAttributes: Attributes): GraphStageLogic = graphStageLogic
}

//this is a sample stateful extension of GraphStageLogic, that accepts first ten elements only
class CountLogic(sinkShape: SinkShape[Int], maxValue: Int) extends GraphStageLogic(sinkShape) {
  var counter: Long = 0

  override def preStart(): Unit = {
    pull(sinkShape.in)
  }

  setHandler(sinkShape.in, new InHandler {
    override def onPush(): Unit = {
      val e = grab(sinkShape.in)
      println("conditional sink : " + e)
      counter = counter + 1
      counter == maxValue match {
        case true => completeStage()
        case false => pull(sinkShape.in)
      }
    }
  })
}


object SampleSinkNotWorking {

  def main(args: Array[String]): Unit = {
    implicit val actorSystem = ActorSystem("NotWroking")
    implicit val actorMaterializer = ActorMaterializer()

    val inlet = Inlet[Int](name = "sampleInlet")
    val sinkShape = SinkShape( inlet )
    val countGraphStateLogic = new CountLogic(sinkShape, 10)

    val sinkGraphStage = new BaseGraphStage[Int](sinkShape, countGraphStateLogic)
    val sink = Sink.fromGraph( sinkGraphStage )

    val graph = GraphDSL.create() { implicit builder =>

      import GraphDSL.Implicits._

      Source(1 to 100) ~> sink

      ClosedShape
    }

    val runnableGraph = RunnableGraph.fromGraph(graph)

    runnableGraph.run()
  }
}

运行上述代码将给ArrayIndexOutOfBoundsException：-

线程“主”中的异常java.lang.ArrayIndexOutOfBoundsException： -1在akka.stream.stage.GraphStageLogic.setHandler（GraphStage.scala：439）在 akka.shapes.examples.notworking.CountLogic。（SampleSinkNotWorking.scala：24）在 akka.shapes.examples.notworking.SampleSinkNotWorking $ .main（SampleSinkNotWorking.scala：46）在 akka.shapes.examples.notworking.SampleSinkNotWorking.main（SampleSinkNotWorking.scala）

我尝试调试，但看起来InLet id为-1，并且没有重置。

但是，当将GraphStateLogic作为构造函数参数传递给GraphState时，为什么不重置它呢？

Answer 1

我有点重构了代码，问题消失了，看看：


class BaseGraphStage(maxValue: Int) extends GraphStage[SinkShape[Int]] {

  val inlet = Inlet[Int](name = "sampleInlet")

  override def createLogic(inheritedAttributes: Attributes): GraphStageLogic =
    new GraphStageLogic(shape) with StageLogging {
      var counter: Int = 0

      setHandler(inlet, new InHandler {
        override def onPush(): Unit = {
          val e = grab(inlet)
          log.info(s"$e is consumed")
          counter += 1
          if (counter == maxValue) {
            completeStage()
          } else {
            pull(inlet)
          }
        }
      })

      override def preStart(): Unit =
        pull(inlet)

      override def postStop(): Unit =
        counter = 0
    }

  override def shape: SinkShape[Int] = SinkShape(inlet)
}

object SampleSinkNotWorking {

  def main(args: Array[String]): Unit = {
    implicit val actorSystem = ActorSystem("NotWorking")
    implicit val actorMaterializer = ActorMaterializer()


    val sink = Sink.fromGraph(new BaseGraphStage(10))

    Source(1 to 100).runWith(sink)
  }
}

不能完全回答您的最后一个问题，但是我认为所有技巧都是关于在图阶段的上下文中创建入口，而不是在入口之外，并使用前后处理程序。希望有帮助。

尝试提取GraphStageLogic以进行自定义有状态实现，然后将其作为参数传递给GraphStage给出了异常

1 个答案: