Please read this:
- http://blog.akka.io/integrations/2016/08/29/connecting-existing-apis
- and this:
http://doc.akka.io/docs/akka/2.4/scala/stream/stream-customize.html

Specifically, your trigger should be implemented as async-callback, as it
comes from the outside but should "wake up" the stage to be able to push
data again.
In your current setup it never "wakes up" since all pulls/pushes have been
processed - the stage has no idea it should do something once you called
open.

On Fri, Oct 14, 2016 at 12:13 AM, regis leray <regis.le...@gmail.com> wrote:

> Hi,
>
> Im currently trying to implement a valve Graph to manage pause/resume. We
> can control the behavior of the graph by using the MaterializeValue
>
> trait ValveSwitch {
>   def open: Unit
>   def close: Unit
> }
>
>
> Current implementation of the valve
>
> 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)
>   }
>
> }
>
>
> The current implementation is pretty simple, each time we are receiving a
> onPull demand we are requesting by doing pull(in).
> When a onPush demand is received we are checking the current state
> - if Open we are doing the default behavior by doing push(out,element)
> - if Close we are putting the element into a queue
>
> 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
>     }
>   })
> }
>
>
> When we are resuming the valve my using the switch.open, we are pushing
> the element
>
> override def open: Unit = {
>
>   mode = ValveMode.Open
>   println(s"pushing $bufferedElement, out is available ? ${isAvailable(out)}")
>
>   bufferedElement.foreach(push(out, _))
>   bufferedElement = List.empty
> }
>
>
> The Current test is failing
>
> "A closed valve" should "emit only 3 elements after it has been open" in {
>
>     val (valve, probe) = Source(1 to 5)
>     .viaMat(new Valve(ValveMode.Closed))(Keep.right) //the current valve by 
> default is closed, dont push any message
>     .toMat(TestSink.probe[Int])(Keep.both)
>     .run()
>
>   probe.request(2)
>   probe.expectNoMsg()
>
>   valve.open //open the valve should emit the previous
>
>
>   probe.expectNext shouldEqual 1 //we never receive the element
>   probe.expectNext shouldEqual 2
>
>   probe.request(3)
>   probe.expectNext shouldEqual 3
>   probe.expectNext shouldEqual 4
>   probe.expectNext shouldEqual 5
>
>   probe.expectComplete()
> }
>
>
> Here the console log
>
> on pull called
> Closed on push called with 1
> pushing Some(1), out is available ? true
>
> Expected OnNext(_), yet no element signaled during 3 seconds
> java.lang.AssertionError: Expected OnNext(_), yet no element signaled during 
> 3 seconds
> at 
> akka.stream.testkit.TestSubscriber$ManualProbe.expectNext(StreamTestKit.scala:268)
> at 
> akka.stream.testkit.TestSubscriber$ManualProbe.expectNext(StreamTestKit.scala:259)
> at 
> com.omsignal.omrun.orchestration.rest.ValveSpec$$anonfun$1.apply(ValveSpec.scala:44)
> at 
> com.omsignal.omrun.orchestration.rest.ValveSpec$$anonfun$1.apply(ValveSpec.scala:34)
>
>
> I'm suspecting the current code to have an issue when we are resuming the
> valve, it doesnt seems the push really works
>
> 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 = Option.empty
>     }
>
>     override def close: Unit = {
>       mode = ValveMode.Closed
>     }
>   }
>
>
> There is definitively something i dont catch up, if anyone could help me
> to see some light....
>
> Here the gist
> https://gist.github.com/regis-leray/013dfe030159bcd890ca0d5cd440c938
>
> Any help would be appreciated
>
> --
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-- 
Cheers,
Konrad 'ktoso' Malawski
Akka <http://akka.io/> @ Typesafe <http://typesafe.com/>

-- 
>>>>>>>>>>      Read the docs: http://akka.io/docs/
>>>>>>>>>>      Check the FAQ: 
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