/** Shut down this instance of the datanode. Returns only after shutdown is complete. */
 public void shutdown() {
   shouldRun = false;
   try {
     if (infoServer != null) infoServer.stop();
   } catch (Exception e) {
     LOG.warn("Exception shutting down SecondaryNameNode", e);
   }
   try {
     if (checkpointImage != null) checkpointImage.close();
   } catch (IOException e) {
     LOG.warn(StringUtils.stringifyException(e));
   }
 }