Adds mapAsync(Unordered) operator samples (#29600)

akka-docs/src/test/scala/docs/stream/operators/sourceorflow/MapAsyncs.scala

@@ -0,0 +1,116 @@
+/*
+ * Copyright (C) 2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.sourceorflow
+
+import akka.NotUsed
+import akka.actor.ActorSystem
+import akka.stream.scaladsl.Sink
+import akka.stream.scaladsl.Source
+import akka.util.Timeout
+
+import scala.concurrent.ExecutionContextExecutor
+import scala.concurrent.Future
+import scala.concurrent.duration._
+import scala.util.Random
+
+/**
+ *
+ */
+object CommonMapAsync {
+  case class Event(sequenceNumber: Int)
+
+  implicit val sys: ActorSystem = ActorSystem("mapAsync-stream")
+  implicit val exCtx: ExecutionContextExecutor = sys.dispatcher
+  implicit val timeout: Timeout = 3.seconds
+
+  // #mapasync-strict-order
+  // #mapasync-concurrent
+  // #mapasyncunordered
+
+  val events: Source[Event, NotUsed] = //...
+    // #mapasync-strict-order
+    // #mapasync-concurrent
+    // #mapasyncunordered
+    Source.fromIterator(() => Iterator.from(1)).throttle(1, 50.millis).map { in =>
+      Event(in)
+    }
+
+  // #mapasync-strict-order
+  // #mapasync-concurrent
+  // #mapasyncunordered
+
+  def eventHandler(event: Event): Future[Int] = {
+    println(s"Processing event $event...")
+    //...
+    // #mapasync-strict-order
+    // #mapasync-concurrent
+    // #mapasyncunordered
+    val result =
+      if (Random.nextInt(5) == 0) {
+        akka.pattern.after(500.millis)(Future.successful(event.sequenceNumber))
+      } else {
+        Future.successful(event.sequenceNumber)
+      }
+    result.map { x =>
+      println(s"Completed processing $x")
+      x
+    }
+    // #mapasync-strict-order
+    // #mapasync-concurrent
+    // #mapasyncunordered
+  }
+  // #mapasync-strict-order
+  // #mapasync-concurrent
+  // #mapasyncunordered
+
+}
+
+object MapAsyncStrictOrder extends App {
+  import CommonMapAsync._
+  // #mapasync-strict-order
+
+  events
+    .mapAsync(1) { in =>
+      eventHandler(in)
+    }
+    .map { in =>
+      println(s"`mapAsync` emitted event number: $in")
+    }
+    // #mapasync-strict-order
+    .runWith(Sink.ignore)
+
+}
+
+object MapAsync extends App {
+  import CommonMapAsync._
+  // #mapasync-concurrent
+
+  events
+    .mapAsync(3) { in =>
+      eventHandler(in)
+    }
+    .map { in =>
+      println(s"`mapAsync` emitted event number: $in")
+    }
+    // #mapasync-concurrent
+    .runWith(Sink.ignore)
+
+}
+
+object MapAsyncUnordered extends App {
+  import CommonMapAsync._
+  // #mapasyncunordered
+
+  events
+    .mapAsyncUnordered(3) { in =>
+      eventHandler(in)
+    }
+    .map { in =>
+      println(s"`mapAsyncUnordered` emitted event number: $in")
+    }
+    // #mapasyncunordered
+    .runWith(Sink.ignore)
+
+}