!clu #3617 API improvements related to CurrentClusterState

* Getter for CurrentClusterState in Cluster extension, updated via
  ClusterReadView
* Remove lazy init of readView. Otherwise the cluster.state will be
  empty on first access, wich is probably surprising
* Subscribe to several cluster event types at once, to ensure *one*
  CurrentClusterEvent followed by change events
* Deprecate publishCurrentClusterState, was a bad idea, use sendCurrentClusterState
  instead
* Possibility to subscribe with InitialStateAsEvents to receive events corresponding
  to CurrentClusterState
* CurrentClusterState not a ClusterDomainEvent, ticket #3614

akka-samples/akka-sample-cluster-java/src/main/java/sample/cluster/simple/SimpleClusterListener.java

@@ -2,8 +2,8 @@ package sample.cluster.simple;
 
 import akka.actor.UntypedActor;
 import akka.cluster.Cluster;
-import akka.cluster.ClusterEvent.ClusterDomainEvent;
-import akka.cluster.ClusterEvent.CurrentClusterState;
+import akka.cluster.ClusterEvent;
+import akka.cluster.ClusterEvent.MemberEvent;
 import akka.cluster.ClusterEvent.MemberUp;
 import akka.cluster.ClusterEvent.MemberRemoved;
 import akka.cluster.ClusterEvent.UnreachableMember;
@@ -14,10 +14,13 @@ public class SimpleClusterListener extends UntypedActor {
   LoggingAdapter log = Logging.getLogger(getContext().system(), this);
   Cluster cluster = Cluster.get(getContext().system());
 
-  //subscribe to cluster changes, MemberUp
+  //subscribe to cluster changes
   @Override
   public void preStart() {
-    cluster.subscribe(getSelf(), ClusterDomainEvent.class);
+    //#subscribe
+    cluster.subscribe(getSelf(), ClusterEvent.initialStateAsEvents(), 
+        MemberEvent.class, UnreachableMember.class);
+    //#subscribe
   }
 
   //re-subscribe when restart
@@ -28,11 +31,7 @@ public class SimpleClusterListener extends UntypedActor {
 
   @Override
   public void onReceive(Object message) {
-    if (message instanceof CurrentClusterState) {
-      CurrentClusterState state = (CurrentClusterState) message;
-      log.info("Current members: {}", state.members());
-
-    } else if (message instanceof MemberUp) {
+    if (message instanceof MemberUp) {
       MemberUp mUp = (MemberUp) message;
       log.info("Member is Up: {}", mUp.member());
 
@@ -44,7 +43,7 @@ public class SimpleClusterListener extends UntypedActor {
       MemberRemoved mRemoved = (MemberRemoved) message;
       log.info("Member is Removed: {}", mRemoved.member());
 
-    } else if (message instanceof ClusterDomainEvent) {
+    } else if (message instanceof MemberEvent) {
       // ignore
 
     } else {

akka-samples/akka-sample-cluster-java/src/main/java/sample/cluster/simple/SimpleClusterListener2.java

@@ -0,0 +1,57 @@
+package sample.cluster.simple;
+
+import akka.actor.UntypedActor;
+import akka.cluster.Cluster;
+import akka.cluster.ClusterEvent.CurrentClusterState;
+import akka.cluster.ClusterEvent.MemberEvent;
+import akka.cluster.ClusterEvent.MemberUp;
+import akka.cluster.ClusterEvent.MemberRemoved;
+import akka.cluster.ClusterEvent.UnreachableMember;
+import akka.event.Logging;
+import akka.event.LoggingAdapter;
+
+public class SimpleClusterListener2 extends UntypedActor {
+  LoggingAdapter log = Logging.getLogger(getContext().system(), this);
+  Cluster cluster = Cluster.get(getContext().system());
+
+  //subscribe to cluster changes
+  @Override
+  public void preStart() {
+    //#subscribe
+    cluster.subscribe(getSelf(), MemberEvent.class, UnreachableMember.class);
+    //#subscribe
+  }
+
+  //re-subscribe when restart
+  @Override
+  public void postStop() {
+    cluster.unsubscribe(getSelf());
+  }
+
+  @Override
+  public void onReceive(Object message) {
+    if (message instanceof CurrentClusterState) {
+      CurrentClusterState state = (CurrentClusterState) message;
+      log.info("Current members: {}", state.members());
+
+    } else if (message instanceof MemberUp) {
+      MemberUp mUp = (MemberUp) message;
+      log.info("Member is Up: {}", mUp.member());
+
+    } else if (message instanceof UnreachableMember) {
+      UnreachableMember mUnreachable = (UnreachableMember) message;
+      log.info("Member detected as unreachable: {}", mUnreachable.member());
+
+    } else if (message instanceof MemberRemoved) {
+      MemberRemoved mRemoved = (MemberRemoved) message;
+      log.info("Member is Removed: {}", mRemoved.member());
+
+    } else if (message instanceof MemberEvent) {
+      // ignore
+
+    } else {
+      unhandled(message);
+    }
+
+  }
+}

akka-samples/akka-sample-cluster-java/src/main/java/sample/cluster/stats/StatsSampleClient.java

@@ -17,9 +17,12 @@ import akka.actor.Address;
 import akka.actor.Cancellable;
 import akka.actor.UntypedActor;
 import akka.cluster.Cluster;
+import akka.cluster.ClusterEvent.UnreachableMember;
+import akka.cluster.ClusterEvent.ReachableMember;
 import akka.cluster.ClusterEvent.CurrentClusterState;
 import akka.cluster.ClusterEvent.MemberEvent;
 import akka.cluster.ClusterEvent.MemberUp;
+import akka.cluster.ClusterEvent.ReachabilityEvent;
 import akka.cluster.Member;
 import akka.cluster.MemberStatus;
 
@@ -44,7 +47,7 @@ public class StatsSampleClient extends UntypedActor {
   //subscribe to cluster changes, MemberEvent
   @Override
   public void preStart() {
-    cluster.subscribe(getSelf(), MemberEvent.class);
+    cluster.subscribe(getSelf(), MemberEvent.class, ReachabilityEvent.class);
   }
 
   //re-subscribe when restart
@@ -91,6 +94,15 @@ public class StatsSampleClient extends UntypedActor {
       MemberEvent other = (MemberEvent) message;
       nodes.remove(other.member().address());
 
+    } else if (message instanceof UnreachableMember) {
+      UnreachableMember unreachable = (UnreachableMember) message;
+      nodes.remove(unreachable.member().address());
+
+    } else if (message instanceof ReachableMember) {
+      ReachableMember reachable = (ReachableMember) message;
+      if (reachable.member().hasRole("compute"))
+        nodes.add(reachable.member().address());
+
     } else {
       unhandled(message);
     }