code: def start(io_loop=None, check_time=500):
      """Begins watching source files for changes.
  
      .. versionchanged:: 4.1
         The ``io_loop`` argument is deprecated.
      """
      io_loop = io_loop or ioloop.IOLoop.current()
      if io_loop in _io_loops:
          return
      _io_loops[io_loop] = True
      if len(_io_loops) > 1:
          gen_log.warning(
              "tornado.autoreload started more than once in the same process"
          )
      modify_times = {}
      callback = functools.partial(_reload_on_update, modify_times)
      scheduler = ioloop.PeriodicCallback(
          callback, check_time, io_loop=io_loop
      )
      scheduler.start()
  
imports: from __future__ import absolute_import, division, print_function
  import os
  import sys
  import functools
  import logging
  import os
  import pkgutil
  import sys
  import traceback
  import types
  import subprocess
  import weakref
  from tornado import ioloop
  from tornado.log import gen_log
  from tornado import process
  from tornado.util import exec_in
label_desc: Use image node_id 1 for calling a global function with example usage: start(io_loop, check_time) without return types