code: @Override
      public void prepare(Map storm_conf) {
          int timeout = Utils.getInt(storm_conf.get(Config.STORM_GROUP_MAPPING_SERVICE_CACHE_DURATION_SECS));
          cachedGroups = new TimeCacheMap<String, Set<String>>(timeout);
      }
docs: Invoked once immediately after construction
  
  @param storm_conf Storm configuration