synchronized private void safelyLoadClustersAndHosts() {
    if (clustersByName == null || clustersById == null ||
        hostsByName == null || hostsById == null ||
        hostClustersMap == null || clusterHostsMap1 == null) {
      loadClustersAndHosts();
    }
  }
Safely initializes all of the in-memory state collections that this class.
<p>
This method is synchronized so that the data can be loaded only if needed.  If most than one of
the relevant get methods are concurrently invoked, this method should ensure that {@link #loadClustersAndHosts()}
will be entered once.  Subsequent calls will bypass {@link #loadClustersAndHosts()} since the
relevant variables will no longer be null.

@see #getClustersByName()
@see #getClustersById()
@see #getHostsByName()
@see #getHostsById()
@see #getClusterHostsMap()
@see #getHostClustersMap()
ambari-server/src/main/java/org/apache/ambari/server/state/cluster/ClustersImpl.java