longshorej · April 4, 2024 22:44 · longshorej · Apr 4, 2024
diff --git a/akka-streams-expand.scala b/akka-streams-expand.scala
 // suppose that isEnabled is expensive, so we want to call it only once, but otherwise reuse the results
 // of the previous call. we can use Akka Streams expand operator to effectively repeat the previous
 // value, and Source.tick to ensure we call only once per second

 import akka.actor.ActorSystem
 import akka.stream.scaladsl.{Sink, Source}

 import scala.concurrent.duration._
 import java.util.concurrent.ThreadLocalRandom

 class Test {
  implicit val system: ActorSystem = ActorSystem("test")

  Source
    .repeat(1)
    .throttle(4, 1.second)
    .scan(0)(_ + _)
    .zip(
      Source
        .tick(0.seconds, 5.second, ())
        .map(_ => isEnabled())
        .expand(Iterator.continually(_))
    )
    .takeWithin(20.seconds)
    .runWith(Sink.foreach(println))


  // an expensive function - only want to call it once per second
  private def isEnabled(): Boolean = {
    val result = ThreadLocalRandom.current().nextBoolean()
    println(s"calculated isEnabled=$result")
    result
  }
 }
	// suppose that isEnabled is expensive, so we want to call it only once, but otherwise reuse the results
	// of the previous call. we can use Akka Streams expand operator to effectively repeat the previous
	// value, and Source.tick to ensure we call only once per second

	import akka.actor.ActorSystem
	import akka.stream.scaladsl.{Sink, Source}

	import scala.concurrent.duration._
	import java.util.concurrent.ThreadLocalRandom

	class Test {
	implicit val system: ActorSystem = ActorSystem("test")

	Source
	.repeat(1)
	.throttle(4, 1.second)
	.scan(0)(_ + _)
	.zip(
	Source
	.tick(0.seconds, 5.second, ())
	.map(_ => isEnabled())
	.expand(Iterator.continually(_))
	)
	.takeWithin(20.seconds)
	.runWith(Sink.foreach(println))


	// an expensive function - only want to call it once per second
	private def isEnabled(): Boolean = {
	val result = ThreadLocalRandom.current().nextBoolean()
	println(s"calculated isEnabled=$result")
	result
	}
	}