title: Error happen python3.6 while using tornado in multi threading
body: <p>I just simply use the tornado application together with threading as the following code:</p>
  
  <pre><code>def MakeApp():
      return tornado.web.Application([(r"/websocket", EchoWebSocket), ])
  
  def run_tornado_websocket():
      app = MakeApp()
      http_server = tornado.httpserver.HTTPServer(app, ssl_options={
          "certfile": os.path.join(os.path.abspath("."), "server.crt"),
          "keyfile": os.path.join(os.path.abspath("."), "server_no_passwd.key"),
          })
  
      http_server.listen(options.port)
      tornado.ioloop.IOLoop.current().start()
  
  if __name__ == '__main__':
      threads = []
      t = threading.Thread(target=run_tornado_websocket, args=())
      threads.append(t)
      for t in threads:
          t.start()
  </code></pre>
  
  <p>It works fine on python3.5.But it fails on python3.6 and the lasted tornado.It gets the error:</p>
  
  <pre><code>Exception in thread Thread-1:
  Traceback (most recent call last):
    File "D:\python3\lib\threading.py", line 916, in _bootstrap_inner
      self.run()
    File "D:\python3\lib\threading.py", line 864, in run
      self._target(*self._args, **self._kwargs)
    File "D:\ssl\ws_server.py", line 49, in run_tornado_websocket
      http_server.listen(options.port)
    File "D:\python3\lib\site-packages\tornado\tcpserver.py", line 145, in listen
      self.add_sockets(sockets)
    File "D:\python3\lib\site-packages\tornado\tcpserver.py", line 159, in add_sockets
      sock, self._handle_connection)
    File "D:\python3\lib\site-packages\tornado\netutil.py", line 219, in add_accept_handler
      io_loop = IOLoop.current()
    File "D:\python3\lib\site-packages\tornado\ioloop.py", line 282, in current
      loop = asyncio.get_event_loop()
    File "D:\python3\lib\asyncio\events.py", line 694, in get_event_loop
      return get_event_loop_policy().get_event_loop()
    File "D:\python3\lib\asyncio\events.py", line 602, in get_event_loop
  % threading.current_thread().name)
  RuntimeError: There is no current event loop in thread 'Thread-1'.
  </code></pre>
  
  <p>I think there are some changes in IOLOOP in python3.6.But I don't know how to fix this and really want to know the reason. </p>