code: public ThreadGroup getSchedulerThreadGroup() {
  
      if (threadGroup == null) {
        threadGroup = new ThreadGroup("QuartzScheduler");
        if (quartzSchedulerResources.getMakeSchedulerThreadDaemon()) {
          threadGroup.setDaemon(true);
        }
      }
  
      return threadGroup;
    }
docs: Returns the name of the thread group for Quartz's main threads.