private ConcurrentHashMap<String, Set<Host>> getClusterHostsMap() {
    if (clusterHostsMap1 == null) {
      safelyLoadClustersAndHosts();
    }
    return clusterHostsMap1;
  }
Gets the internal cluster/hosts map, ensuring that the relevant data has been previously initialized.

@return a map of the requested data
ambari-server/src/main/java/org/apache/ambari/server/state/cluster/ClustersImpl.java