@Override
        public Object call() throws Exception {
          getController().createHostComponents(requests, true);
          return null;
        }
When config groups are created using Blueprints these are created when
hosts join a hostgroup and are added to the corresponding config group.
Since hosts join in parallel there might be a race condition in creating
the config group a host is to be added to. Thus we need to synchronize
the creation of config groups with the same name.
ambari-server/src/main/java/org/apache/ambari/server/topology/AmbariContext.java