+doc #19429 initial merge of docs-dev and docs

akka-docs/rst/scala/code/docs/stream/cookbook/RecipeWorkerPool.scala

@@ -0,0 +1,48 @@
+package docs.stream.cookbook
+
+import akka.stream.FlowShape
+import akka.stream.scaladsl._
+import akka.testkit.TestProbe
+
+import scala.concurrent.Await
+import scala.concurrent.duration._
+
+class RecipeWorkerPool extends RecipeSpec {
+
+  "Recipe for a pool of workers" must {
+
+    "work" in {
+      val myJobs = Source(List("1", "2", "3", "4", "5"))
+      type Result = String
+
+      val worker = Flow[String].map(_ + " done")
+
+      //#worker-pool
+      def balancer[In, Out](worker: Flow[In, Out, Any], workerCount: Int): Flow[In, Out, Unit] = {
+        import GraphDSL.Implicits._
+
+        Flow.fromGraph(GraphDSL.create() { implicit b =>
+          val balancer = b.add(Balance[In](workerCount, waitForAllDownstreams = true))
+          val merge = b.add(Merge[Out](workerCount))
+
+          for (_ <- 1 to workerCount) {
+            // for each worker, add an edge from the balancer to the worker, then wire
+            // it to the merge element
+            balancer ~> worker ~> merge
+          }
+
+          FlowShape(balancer.in, merge.out)
+        })
+      }
+
+      val processedJobs: Source[Result, Unit] = myJobs.via(balancer(worker, 3))
+      //#worker-pool
+
+      Await.result(processedJobs.grouped(10).runWith(Sink.head), 3.seconds).toSet should be(Set(
+        "1 done", "2 done", "3 done", "4 done", "5 done"))
+
+    }
+
+  }
+
+}