CODEWITHSUNDEEP
scalaakkaakka-stream
ryo
ryo

Reputation: 2167

Broadcast and Concat don't work in Akka Stream

I want to create a graph with a Broadcast and a Concat in Akka Stream, but the following code doesn't work. I want to know why it doesn't work.

  val src = Source(1 to 3)
  val sink = Sink.foreach(println)
  RunnableGraph.fromGraph(GraphDSL.create() { implicit b =>
    import GraphDSL.Implicits._
    val bcast = b.add(Broadcast[Int](2))
    val concat = b.add(Concat[Int](2))

    src  ~> bcast ~> concat ~> sink
            bcast ~> concat

    ClosedShape
  }).run()

My expected output is 

1
2
3
1
2
3

But, actually, nothing is outputted. I would like you to tell why my code doesn't work.

Upvotes: 0

Views: 393

Answers (1)

Viktor Klang
Viktor Klang

Reputation: 26589

Broadcast can only work if its downstreams all have demand, and concat only demands from one upstream at a time (otherwise you'd want to have merge etc), and thus broadcast cannot broadcast anything.

Upvotes: 2

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