public VisibilityLabelService getVisibilityLabelService() {
    // By the time this method is called, the singleton instance of visibilityLabelService should
    // have been created. And it will be created as getVisibilityLabelService(Configuration conf)
    // is called from VC#start() and that will be the 1st thing core code do with any CP.
    if (this.visibilityLabelService == null) {
      throw new IllegalStateException("VisibilityLabelService not yet instantiated");
    }
    return this.visibilityLabelService;
  }
@return singleton instance of {@link VisibilityLabelService}.
@throws IllegalStateException if this called before initialization of singleton instance.
hbase-server/src/main/java/org/apache/hadoop/hbase/security/visibility/VisibilityLabelServiceManager.java