Cluster member age, and usage in singleton, see #3195

* Assign internal upNumber when member is moved to Up
* Public API Member.isOlder
* Change cluster singleton to use oldest member instead of leader
* Update samples and docs

akka-contrib/src/test/java/akka/contrib/pattern/ClusterSingletonManagerTest.java

@@ -0,0 +1,119 @@
+/**
+ *  Copyright (C) 2009-2013 Typesafe Inc. <http://www.typesafe.com>
+ */
+
+package akka.contrib.pattern;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+import java.util.SortedSet;
+import java.util.TreeSet;
+
+import akka.actor.ActorSystem;
+import akka.actor.ActorRef;
+import akka.actor.ActorSelection;
+import akka.actor.Props;
+import akka.actor.UntypedActor;
+import akka.cluster.Cluster;
+import akka.cluster.Member;
+import akka.cluster.ClusterEvent.CurrentClusterState;
+import akka.cluster.ClusterEvent.MemberEvent;
+import akka.cluster.ClusterEvent.MemberUp;
+import akka.cluster.ClusterEvent.MemberRemoved;
+
+public class ClusterSingletonManagerTest {
+
+  public void demo() {
+    final ActorSystem system = null;
+    final ActorRef queue = null;
+    final ActorRef testActor = null;
+
+    //#create-singleton-manager
+    system.actorOf(
+      ClusterSingletonManager.defaultProps("consumer", new End(), "worker",
+        new ClusterSingletonPropsFactory() {
+          @Override
+          public Props create(Object handOverData) {
+            return Props.create(Consumer.class, handOverData, queue, testActor);
+          }
+        }), "singleton");
+    //#create-singleton-manager
+  }
+
+  static//documentation of how to keep track of the oldest member in user land
+  //#singleton-proxy
+  public class ConsumerProxy extends UntypedActor {
+
+    final Cluster cluster = Cluster.get(getContext().system());
+
+    final Comparator<Member> ageComparator = new Comparator<Member>() {
+      public int compare(Member a, Member b) {
+        if (a.isOlderThan(b))
+          return -1;
+        else if (b.isOlderThan(a))
+          return 1;
+        else
+          return 0;
+      }
+    };
+    final SortedSet<Member> membersByAge = new TreeSet<Member>(ageComparator);
+
+    final String role = "worker";
+
+    //subscribe to cluster changes
+    @Override
+    public void preStart() {
+      cluster.subscribe(getSelf(), MemberEvent.class);
+    }
+
+    //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;
+        List<Member> members = new ArrayList<Member>();
+        for (Member m : state.getMembers()) {
+          if (m.hasRole(role))
+            members.add(m);
+        }
+        membersByAge.clear();
+        membersByAge.addAll(members);
+
+      } else if (message instanceof MemberUp) {
+        Member m = ((MemberUp) message).member();
+        if (m.hasRole(role))
+          membersByAge.add(m);
+
+      } else if (message instanceof MemberRemoved) {
+        Member m = ((MemberUp) message).member();
+        if (m.hasRole(role))
+          membersByAge.remove(m);
+
+      } else if (message instanceof MemberEvent) {
+        // not interesting
+
+      } else if (!membersByAge.isEmpty()) {
+        currentMaster().tell(message, getSender());
+
+      }
+    }
+
+    ActorSelection currentMaster() {
+      return getContext().actorSelection(membersByAge.first().address() +
+          "/user/singleton/statsService");
+    }
+
+  }
+  //#singleton-proxy
+
+
+  public static class End {}
+
+  public static class Consumer {}
+}