private void checkGroupName(String groupName) throws ConstraintException {
    if (!groupName.matches("[a-zA-Z0-9_]+")) {
      throw new ConstraintException("RSGroup name should only contain alphanumeric characters");
    }
  }
Update cache of rsgroups. Caller must be synchronized on 'this'.
@param currentGroups Current list of Groups.
hbase-server/src/main/java/org/apache/hadoop/hbase/rsgroup/RSGroupInfoManagerImpl.java