Merge pull request #18441 from akka/wip-18245-registerOnMemberRemoved-example-patriknw

=clu #18245 Improve registerOnMemberRemoved example

akka-cluster/src/main/scala/akka/cluster/Cluster.scala

@@ -339,7 +339,7 @@ class Cluster(val system: ExtendedActorSystem) extends Extension {
 
   /**
    * The supplied thunk will be run, once, when current cluster member is `Removed`.
-   * and if the cluster have been shutdown,that thunk will run on the caller thread immediately.
+   * If the cluster has already been shutdown the thunk will run on the caller thread immediately.
    * Typically used together `cluster.leave(cluster.selfAddress)` and then `system.shutdown()`.
    */
   def registerOnMemberRemoved[T](code: ⇒ T): Unit =
@@ -347,7 +347,7 @@ class Cluster(val system: ExtendedActorSystem) extends Extension {
 
   /**
    * Java API: The supplied thunk will be run, once, when current cluster member is `Removed`.
-   * and if the cluster have been shutdown,that thunk will run on the caller thread immediately.
+   * If the cluster has already been shutdown the thunk will run on the caller thread immediately.
    * Typically used together `cluster.leave(cluster.selfAddress)` and then `system.shutdown()`.
    */
   def registerOnMemberRemoved(callback: Runnable): Unit = {

akka-docs/rst/java/cluster-usage.rst

@@ -333,8 +333,7 @@ How To Cleanup when Member is Removed
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 You can do some clean up in a ``registerOnMemberRemoved`` callback, which will
-be invoked when the current member status is changed to 'Removed' or the cluster have been shutdown,i.e.
-terminate the actor system.
+be invoked when the current member status is changed to 'Removed' or the cluster have been shutdown.
 
 For example, this is how to shut down the ``ActorSystem`` and thereafter exit the JVM:
 

akka-docs/rst/scala/cluster-usage.rst

@@ -327,8 +327,7 @@ How To Cleanup when Member is Removed
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 You can do some clean up in a ``registerOnMemberRemoved`` callback, which will
-be invoked when the current member status is changed to 'Removed' or the cluster have been shutdown,i.e.
-terminate the actor system.
+be invoked when the current member status is changed to 'Removed' or the cluster have been shutdown.
 
 For example, this is how to shut down the ``ActorSystem`` and thereafter exit the JVM:
 

akka-samples/akka-sample-cluster-java/src/main/java/sample/cluster/factorial/FactorialFrontendMain.java

@@ -1,8 +1,10 @@
 package sample.cluster.factorial;
 
-import java.util.concurrent.TimeUnit;
 
-import scala.concurrent.duration.FiniteDuration;
+import java.util.concurrent.TimeoutException;
+import java.util.concurrent.TimeUnit;
+import scala.concurrent.Await;
+import scala.concurrent.duration.Duration;
 import com.typesafe.config.Config;
 import com.typesafe.config.ConfigFactory;
 
@@ -38,18 +40,29 @@ public class FactorialFrontendMain {
       public void run() {
         // exit JVM when ActorSystem has been terminated
         final Runnable exit = new Runnable() {
-          @Override
-          public void run() {
-            System.exit(-1);
+          @Override public void run() {
+            System.exit(0);
           }
         };
         system.registerOnTermination(exit);
-        // in case ActorSystem shutdown takes longer than 10 seconds, 
-        // exit the JVM forcefully anyway
-        system.scheduler().scheduleOnce(FiniteDuration.create(10, TimeUnit.SECONDS), 
-            exit, system.dispatcher());
+
         // shut down ActorSystem
         system.terminate();
+
+        // In case ActorSystem shutdown takes longer than 10 seconds,
+        // exit the JVM forcefully anyway.
+        // We must spawn a separate thread to not block current thread,
+        // since that would have blocked the shutdown of the ActorSystem.
+        new Thread() {
+          @Override public void run(){
+            try {
+              Await.ready(system.whenTerminated(), Duration.create(10, TimeUnit.SECONDS));
+            } catch (Exception e) {
+              System.exit(-1);
+            }
+
+          }
+        }.start();
       }
     });
     //#registerOnRemoved

akka-samples/akka-sample-cluster-scala/src/main/scala/sample/cluster/factorial/FactorialFrontend.scala

@@ -9,6 +9,8 @@ import akka.actor.Props
 import akka.cluster.Cluster
 import akka.routing.FromConfig
 import akka.actor.ReceiveTimeout
+import scala.util.Try
+import scala.concurrent.Await
 
 //#frontend
 class FactorialFrontend(upToN: Int, repeat: Boolean) extends Actor with ActorLogging {
@@ -61,12 +63,20 @@ object FactorialFrontend {
     //#registerOnRemoved
     Cluster(system).registerOnMemberRemoved {
       // exit JVM when ActorSystem has been terminated
-      system.registerOnTermination(System.exit(-1))
-      // in case ActorSystem shutdown takes longer than 10 seconds,
-      // exit the JVM forcefully anyway
-      system.scheduler.scheduleOnce(10.seconds)(System.exit(-1))(system.dispatcher)
+      system.registerOnTermination(System.exit(0))
       // shut down ActorSystem
       system.terminate()
+
+      // In case ActorSystem shutdown takes longer than 10 seconds,
+      // exit the JVM forcefully anyway.
+      // We must spawn a separate thread to not block current thread,
+      // since that would have blocked the shutdown of the ActorSystem.
+      new Thread {
+        override def run(): Unit = {
+          if (Try(Await.ready(system.whenTerminated, 10.seconds)).isFailure)
+            System.exit(-1)
+        }
+      }.start()
     }
     //#registerOnRemoved