How to stop the tornado web server with ctrl+c? - python-2.7

Question

I am new to tornado web server. When I start the tornado web server using python main_tornado.py It is working. Please see the below code.
import tornado.ioloop
import tornado.web
class MainHandler(tornado.web.RequestHandler):
def get(self):
self.write("Hello, world")
application = tornado.web.Application([
(r"/", MainHandler),
])
if __name__ == "__main__":
application.listen(8888)
tornado.ioloop.IOLoop.instance().start()
When I stop the server using CTRL+C it gave the following error.
^CTraceback (most recent call last):
File "main_tornado.py", line 19, in <module>
tornado.ioloop.IOLoop.instance().start()
File "/home/nyros/Desktop/NewWeb/venv/lib/python3.2/site-packages/tornado/ioloop.py", line 301, in start
event_pairs = self._impl.poll(poll_timeout)
KeyboardInterrupt
Please solve my problem. Thanks..

Answer 1

You can stop Tornado main loop with tornado.ioloop.IOLoop.instance().stop(). To have this method called after passing signal with Ctrl+C you can periodically check global flag to test if main loop should end and register handler for SIGINT signal which will change value of this flag:
#!/usr/bin/python
# -*- coding: utf-8 -*-
import signal
import logging
import tornado.ioloop
import tornado.web
import tornado.options
class MainHandler(tornado.web.RequestHandler):
def get(self):
self.write("Hello, world")
class MyApplication(tornado.web.Application):
is_closing = False
def signal_handler(self, signum, frame):
logging.info('exiting...')
self.is_closing = True
def try_exit(self):
if self.is_closing:
# clean up here
tornado.ioloop.IOLoop.instance().stop()
logging.info('exit success')
application = MyApplication([
(r"/", MainHandler),
])
if __name__ == "__main__":
tornado.options.parse_command_line()
signal.signal(signal.SIGINT, application.signal_handler)
application.listen(8888)
tornado.ioloop.PeriodicCallback(application.try_exit, 100).start()
tornado.ioloop.IOLoop.instance().start()
Output:
$ python test.py
[I 181209 22:13:43 web:2162] 200 GET / (127.0.0.1) 0.92ms
^C[I 181209 22:13:45 test:21] exiting...
[I 181209 22:13:45 test:28] exit success
UPDATE
I've just saw in question Tornado long polling requests this simple solution:
try:
tornado.ioloop.IOLoop.instance().start()
except KeyboardInterrupt:
tornado.ioloop.IOLoop.instance().stop()
Obviously, this is a less safe way.
UPDATE
Edited the code to remove use of global.

Answer 2

You can simply stop the Tornado ioloop from a signal handler. It should be safe thanks to add_callback_from_signal() method, the event loop will exit nicely, finishing any eventually concurrently running task.
import tornado.ioloop
import tornado.web
import signal
class MainHandler(tornado.web.RequestHandler):
def get(self):
self.write("Hello, world")
application = tornado.web.Application([
(r"/", MainHandler),
])
def sig_exit(signum, frame):
tornado.ioloop.IOLoop.instance().add_callback_from_signal(do_stop)
def do_stop(signum, frame):
tornado.ioloop.IOLoop.instance().stop()
if __name__ == "__main__":
application.listen(8888)
signal.signal(signal.SIGINT, sig_exit)
tornado.ioloop.IOLoop.instance().start()

Answer 3

The code is OK. The CTRL+C generates KeyboardInterrupt. To stop the server you can use CTRL+Pause Break(on windows) instead of CTRL+C. On linux CTRL+C also generates the KeyboardInterrupt also. If you will use CTRL+Z program will stop but port gets busy.

Answer 4

I'd say the cleanest, safest and most portable solution would be to put all closing and clean-up calls in a finally block instead of relying on KeyboardInterrupt exception:
import tornado.ioloop
import tornado.web
class MainHandler(tornado.web.RequestHandler):
def get(self):
self.write("Hello, world")
application = tornado.web.Application([
(r"/", MainHandler),
])
# .instance() is deprecated in Tornado 5
loop = tornado.ioloop.IOLoop.current()
if __name__ == "__main__":
try:
print("Starting server")
application.listen(8888)
loop.start()
except KeyboardInterrupt:
pass
finally:
loop.stop() # might be redundant, the loop has already stopped
loop.close(True) # needed to close all open sockets
print("Server shut down, exiting...")