docs: private DirectoryLookupService getLookupService(){
          if(lookupService == null){
              synchronized(this){
                  if(lookupService == null){
                      boolean cacheEnabled = Configurations.getBoolean(SD_API_CACHE_ENABLED_PROPERTY,
                              SD_API_CACHE_ENABLED_DEFAULT);
                      if(cacheEnabled){
                          CachedDirectoryLookupService service = new CachedDirectoryLookupService(directoryServiceClientManager);
                          service.start();
                          lookupService = service;
                          LOGGER.info("Created the CachedDirectoryLookupService in LookupManager");
                      } else {
                          lookupService = new DirectoryLookupService(directoryServiceClientManager);
                          LOGGER.info("Created the DirectoryLookupService in LookupManager");
                      }
                  }
              }
          }
          return lookupService;
      }