如何从类内部使递归akka流“可切换”

Question

I have a class with endless stream that defined as follows:

abstract class StreamWrapper() {

  def doStuff: Future[Unit] = ???

  def recursiveStream(): Unit =
    events.mapAsync(parallelism)(doStuff)
      .runWith(Sink.fold(???))
      .onComplete( 
        actorSystem.scheduler.scheduleOnce(delay)(recursiveStream())
                                               // ^-- recursion --^
      )

}

I wan't to be able to turn off/on this stream from doStuff function (in my case I have a circuit breaker inside, so I want to turn on/off recursiveStream via it's callbacks).

Easiest way to solve this to introduce atomic boolean, check it in recursiveStream method and toggle it inside doStuff :

abstract class StreamWrapper() {

  private val enabled = new AtomicBoolean(true)

  def doStuff: Future[Unit] = ??? // toggle enabled here

  def recursiveStream(): Unit = 
    if (enabled)
      events.mapAsync(parallelism)(doStuff)
        .runWith(Sink.fold(???))
        .onComplete( 
          actorSystem.scheduler.scheduleOnce(delay)(recursiveStream())
        )
    else log.info("Stream is currently offline...")

}

But it feels like there are may be more idiomatic solution to do it using Scala and/or Akka features. Can you suggest another method to solve this problem?

Answer 1

Use Valve from the Akka Streams Contrib project :

Materializes into a Future of ValveSwitch which provides a the method flip that stops or restarts the flow of elements passing through the stage. As long as the valve is closed it will backpressure.

Examples of its use are found in ValveSpec .