Add thread-safety support to the Hazelcast-based notification framework.

Change-Id: I606f6ccb417c733903b7d8305d8d23b434417c2e
diff --git a/src/main/java/net/onrc/onos/datagrid/HazelcastDatagrid.java b/src/main/java/net/onrc/onos/datagrid/HazelcastDatagrid.java
index b240299..8d797e7 100755
--- a/src/main/java/net/onrc/onos/datagrid/HazelcastDatagrid.java
+++ b/src/main/java/net/onrc/onos/datagrid/HazelcastDatagrid.java
@@ -762,8 +762,9 @@
      * @param typeV the type of the Value in the Key-Value store.
      * @return the event channel for the channel name.
      */
-    private <K, V> IEventChannel<K, V> createChannelImpl(String channelName,
-					     Class<K> typeK, Class<V> typeV) {
+    private synchronized <K, V> IEventChannel<K, V> createChannelImpl(
+					String channelName,
+					Class<K> typeK, Class<V> typeV) {
 	IEventChannel<K, V> castedEventChannel;
 	IEventChannel<?, ?> genericEventChannel =
 	    eventChannels.get(channelName);