tornado 在启动时候，启动1个线程，实现crontab的功能

from tornado import web, ioloop
import datetime
period = 5 * 1000   # every 5 s
class MainHandler(web.RequestHandler):
    def get(self):
        self.write('Hello Tornado')
def like_cron():
    print datetime.datetime.now()
def xiaorui():
    print 'xiaorui 2s'
def lee():
    print '  wansuilee 3s'
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
if __name__ == '__main__':
    application = web.Application([
        (r'/', MainHandler),
        ])
    application.listen(80)
    ioloop.PeriodicCallback(like_cron, period).start()  # start scheduler
    ioloop.PeriodicCallback(xiaorui, 1000).start()  # start scheduler
    ioloop.PeriodicCallback(lee, 3000).start()  # start scheduler
    ioloop.IOLoop.instance().start()