Fix potential race conditions in HazelcastLeadershipService

Change-Id: Iac232652155830c8e054760ea371ffb5639cf464

@@ -166,8 +166,8 @@ public class HazelcastLeadershipService implements LeadershipService,
         checkArgument(path != null);
         Topic topic = topics.get(path);
         if (topic != null) {
-            topic.stop();
             topics.remove(path, topic);
+            topic.stop();
         }
     }
 
@@ -213,6 +213,7 @@ public class HazelcastLeadershipService implements LeadershipService,
             topic = new Topic(topicName);
             Topic oldTopic = topics.putIfAbsent(topicName, topic);
             if (oldTopic == null) {
+                // encountered new topic, start periodic processing
                 topic.start();
             } else {
                 topic = oldTopic;
@@ -285,7 +286,11 @@ public class HazelcastLeadershipService implements LeadershipService,
         /**
          * Starts operation.
          */
-        private void start() {
+        private synchronized void start() {
+            if (!isShutdown) {
+                // already running
+                return;
+            }
             isShutdown = false;
             String threadPoolName = "onos-leader-election-" + topicName + "-%d";
             leaderElectionExecutor = Executors.newScheduledThreadPool(2,
@@ -303,13 +308,14 @@ public class HazelcastLeadershipService implements LeadershipService,
         /**
          * Runs for leadership.
          */
-        private void runForLeadership() {
+        private synchronized void runForLeadership() {
             if (isRunningForLeadership) {
                 return;         // Nothing to do: already running
             }
             if (isShutdown) {
                 start();
             }
+            isRunningForLeadership = true;
             String lockHzId = "LeadershipService/" + topicName + "/lock";
             String termHzId = "LeadershipService/" + topicName + "/term";
             leaderLock = storeService.getHazelcastInstance().getLock(lockHzId);
@@ -326,7 +332,7 @@ public class HazelcastLeadershipService implements LeadershipService,
         /**
          * Stops leadership election for the topic.
          */
-        private void stop() {
+        private synchronized void stop() {
             isShutdown = true;
             isRunningForLeadership = false;
             // getLockFuture.cancel(true);
@@ -454,6 +460,7 @@ public class HazelcastLeadershipService implements LeadershipService,
                     continue;
                 }
 
+                try {
                     synchronized (this) {
                         //
                         // This instance is now the leader
@@ -469,7 +476,6 @@ public class HazelcastLeadershipService implements LeadershipService,
                         leaderTopic.publish(SERIALIZER.encode(leadershipEvent));
                     }
 
-                try {
                     // Sleep forever until interrupted
                     Thread.sleep(Long.MAX_VALUE);
                 } catch (InterruptedException e) {
@@ -479,8 +485,8 @@ public class HazelcastLeadershipService implements LeadershipService,
                     //
                     log.debug("Leader Interrupted for topic {}",
                               topicName);
-                }
 
+                } finally {
                     synchronized (this) {
                         // If we reach here, we should release the leadership
                         log.debug("Leader Lock Released for topic {}", topicName);
@@ -495,7 +501,8 @@ public class HazelcastLeadershipService implements LeadershipService,
                         leaderLock.unlock();
                     }
                 }
-
+            }
+            isRunningForLeadership = false;
         }
 
         // Globally guarded by the leadership lock for this term