code: public void shutdown()
    {
      log.info("Shutting down...");
      isShutdownRequested = true;
  
      try
      {
        mainThread.join();
      }
      catch (InterruptedException e)
      {
        log.error(
          "Interrupted which waiting on main daemon thread to complete.");
      }
    }
docs: shutdown the AnnisService - ensure that current work load finishes