code: public synchronized void shutdown() {
      if (!isActive) {
        return;
      }
      log.info("Shutting down the default async job executor [{}].", getClass().getName());
      
      if (timerJobRunnable != null) {
        timerJobRunnable.stop();
      }
      if (asyncJobsDueRunnable != null) {
        asyncJobsDueRunnable.stop();
      }
      if (resetExpiredJobsRunnable != null) {
        resetExpiredJobsRunnable.stop();
      }
      
      stopResetExpiredJobsThread();
      stopTimerAcquisitionThread();
      stopJobAcquisitionThread();
      stopExecutingAsyncJobs();
  
      timerJobRunnable = null;
      asyncJobsDueRunnable = null;
      resetExpiredJobsRunnable = null;
      
      isActive = false;
    }
docs: Shuts down the whole job executor