斯卡拉 – Akka Streams的工人池

def balancer[In,Out](worker: Flow[In,Out,NotUsed],workerCount: Int): Flow[In,NotUsed] = {
    import GraphDSL.Implicits._

    Flow.fromGraph(GraphDSL.create() { implicit b =>
      val balancer = b.add(Balance[In](workerCount))
      val merge = b.add(Merge[Out](workerCount))

      for (_ <- 1 to workerCount) {
        balancer ~> worker ~> merge
      }
      FlowShape(balancer.in,merge.out)
    })
  }

然后我用这个函数并行运行一个流程：

def main(args: Array[String]) {
    val system = ActorSystem()
    implicit val mat = ActorMaterializer.create(system)

    val flow = Flow[Int].map(e => {
      println(e)
      Thread.sleep(1000) // 1 second
      e
    })

    Source(Range.apply(1,10).toList)
      .via(balancer(flow,3))
      .runForeach(e => {})
  }

我得到预期的输出1,2,3,4,5,6,7,8,9,但数字以每秒1的速率出现(没有并行性).我做错了什么？