code: public static void shutdown() throws SundialSchedulerException {
  
      logger.debug("shutdown() called.");
  
      try {
        getScheduler().shutdown();
        scheduler = null;
      } catch (Exception e) {
        throw new SundialSchedulerException("COULD NOT SHUTDOWN SCHEDULER!!!", e);
      }
    }
docs: Halts the Scheduler's firing of Triggers, and cleans up all resources associated with the
  Scheduler.