docs: public Scheduler start() {
  		synchronized (lock) {
  			if (this.started) {
  				throw new CronException("Schedule is started!");
  			}
  
  			// 无界线程池，确保每一个需要执行的线程都可以及时运行，同时复用已有现成避免线程重复创建
  			this.threadExecutor = ExecutorBuilder.create().useSynchronousQueue().setThreadFactory(//
  					ThreadFactoryBuilder.create().setNamePrefix("hutool-cron-").setDaemon(this.daemon).build()//
  			).build();
  			this.taskLauncherManager = new TaskLauncherManager(this);
  			this.taskExecutorManager = new TaskExecutorManager(this);
  
  			// Start CronTimer
  			timer = new CronTimer(this);
  			timer.setDaemon(this.daemon);
  			timer.start();
  			this.started = true;
  		}
  		return this;
  	}