docs: @Override
      public void shutdown() {
  
          // prevent reentrant invocation
          if(isShutdown())
              return;
  
          // perform shutdown login in base
          super.shutdown();
  
          try {
              // if a monitor is running, then shut it down now
              if (monitor != null) {
                  // shutdown monitoring thread
                  monitor.shutdown();
                  monitor = null;
              }
          } catch (Exception e) {
              throw new RuntimeException(e);
          }
      }