Hi,
I'm trying to implements a way to control a flow (start/stop), nothing was
implemented yet in the core of akka-stream
My current implementation looks like this.
trait ValveSwitch {
def open: Unit
def close: Unit
}
class Valve[A](mode: ValveMode = ValveMode.Open) extends
GraphStageWithMaterializedValue[FlowShape[A, A], ValveSwitch] {
override val shape = FlowShape(Inlet[A]("valve.in"),
Outlet[A]("valve.out"))
override def createLogicAndMaterializedValue(inheritedAttributes:
Attributes): (GraphStageLogic, ValveSwitch) = {
val logic = new ValveGraphStageLogic(shape, mode)
(logic, logic.switch)
}
private class ValveGraphStageLogic(shape: Shape, var mode: ValveMode)
extends GraphStageLogic(shape){
import shape._
var bufferedElement = List.empty[A]
val switch = new ValveSwitch {
override def open: Unit = {
mode = ValveMode.Open
println(s"pushing $bufferedElement, out is available ?
${isAvailable(out)}")
bufferedElement.foreach(push(out, _))
bufferedElement = List.empty
}
override def close: Unit = {
mode = ValveMode.Closed
}
}
setHandler(in, new InHandler {
override def onPush(): Unit = {
val element = grab(in) //acquires the element that has been
received during an onPush
println(s"${mode} on push called with $element")
if (mode == ValveMode.Open) {
push(out, element) //push directly the element on the out port
} else {
bufferedElement = bufferedElement :+ element
}
}
})
setHandler(out, new OutHandler {
override def onPull(): Unit = {
println("on pull called")
pull(in) //request the next element on in port
}
})
}
}
trait ValveMode
object ValveMode {
case object Open extends ValveMode
case object Closed extends ValveMode
}
====
My current unit test is failing. due to the fact when i open the valve, i
never received the previous message.
It seems even if i push the element through ( valve.open ) the sink never
receive the element
class ValveSpec extends FlatSpec {
implicit val system = ActorSystem()
implicit val materializer = ActorMaterializer()
implicit val executionContext = materializer.executionContext
"A closed valve" should "emit only 3 elements after it has been open" in {
val (valve, probe) = Source(1 to 3)
.viaMat(new Valve(ValveMode.Closed))(Keep.right)
.toMat(TestSink.probe[Int])(Keep.both)
.run()
probe.request(1)
probe.expectNoMsg()
valve.open
probe.expectNext(1)
probe.request(2)
probe.expectNext(2, 3)
probe.expectComplete()
}
}
Here the gist
https://gist.github.com/regis-leray/013dfe030159bcd890ca0d5cd440c938
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