Merge pull request #29356 from ignasi35/monitor-operator-sample-code

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

@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.stream.operators.sourceorflow
+
+import akka.NotUsed
+import akka.actor.ActorSystem
+import akka.stream.FlowMonitor
+import akka.stream.FlowMonitorState
+import akka.stream.scaladsl.Keep
+import akka.stream.scaladsl.Sink
+import akka.stream.scaladsl.Source
+
+import scala.concurrent.ExecutionContextExecutor
+import scala.concurrent.duration._
+
+class Monitor {
+
+  implicit val system = ActorSystem("monitor-sample-sys2")
+  implicit val executionContext: ExecutionContextExecutor = system.dispatcher
+
+  // #monitor
+  val source: Source[Int, NotUsed] =
+    Source.fromIterator(() => Iterator.from(0))
+
+  def printMonitorState(flowMonitor: FlowMonitor[Int]) =
+    flowMonitor.state match {
+      case FlowMonitorState.Initialized =>
+        println("Stream is initialized but hasn't processed any element")
+      case FlowMonitorState.Received(msg) =>
+        println(s"Last element processed: $msg")
+      case FlowMonitorState.Failed(cause) =>
+        println(s"Stream failed with cause $cause")
+      case FlowMonitorState.Finished => println(s"Stream completed already")
+    }
+
+  val monitoredSource: Source[Int, FlowMonitor[Int]] = source.take(6).throttle(5, 1.second).monitorMat(Keep.right)
+  val (flowMonitor, futureDone) =
+    monitoredSource.toMat(Sink.foreach(println))(Keep.both).run()
+
+  // If we peek in the monitor too early, it's possible it was not initialized yet.
+  printMonitorState(flowMonitor)
+
+  // Periodically check the monitor
+  Source.tick(200.millis, 400.millis, "").runForeach(_ => printMonitorState(flowMonitor))
+
+  // #monitor
+  futureDone.onComplete(_ => system.terminate())
+
+}