code: @Override
      public void close() throws IOException {
          try {
              if (_ds != null && _ds.isClosed() == false) {
                  _ds.close();
              }
          } finally {
              if (_dsm != null && _dsm.isClosed() == false) {
                  _dsm.close();
              }
          }
      }
docs: Close the underline data source