@Override
  public int getLabelOrdinal(String label) {
    Integer ordinal = null;
    this.lock.readLock().lock();
    try {
      ordinal = labels.get(label);
    } finally {
      this.lock.readLock().unlock();
    }
    if (ordinal != null) {
      return ordinal.intValue();
    }
    // 0 denotes not available
    return VisibilityConstants.NON_EXIST_LABEL_ORDINAL;
  }
@param label Not null label string
@return The ordinal for the label. The ordinal starts from 1. Returns 0 when passed a non
        existing label.
hbase-server/src/main/java/org/apache/hadoop/hbase/security/visibility/VisibilityLabelsCache.java