asyncio loop's add_signal_handler() in Windows

Question

I'm currently porting a Python project from Linux to Windows (using Anaconda Python 3.6). Everything works perfectly, I just cannot get a graceful exit of the asyncio loop working.

In Linux I'm doing the following:

class GracefulExit(SystemExit):
    code = 1

def raise_graceful_exit():
    raise GracefulExit()

loop = asyncio.get_event_loop()
loop.add_signal_handler(signal.SIGINT, raise_graceful_exit)
loop.add_signal_handler(signal.SIGTERM, raise_graceful_exit)

try:
    loop.run_forever()
except GracefulExit:
    pass

shutdown()

In Windows, unfortunately I get a NotImplementedError on add_signal_handler. Without this, of course I never get a chance for a clean shutdown of the program.

Any ideas on how to solve this? Thanks.

Answer 1

Actually you can implement kind of a cross-platform python signal handler in your python script that works on both Unix/Linux and Windows, python has a standard signal library, so you can do something like this

import asyncio
import signal


class GracefulExit(SystemExit):
    code = 1


def raise_graceful_exit(*args):
    loop.stop()
    print("Gracefully shutdown")
    raise GracefulExit()


def do_something():
    while True:
        pass


loop = asyncio.get_event_loop()
signal.signal(signal.SIGINT, raise_graceful_exit)
signal.signal(signal.SIGTERM, raise_graceful_exit)

try:
    loop.run_forever(do_something())
except GracefulExit:
    pass
finally:
    loop.close()

It does not behave exactly the same on Windows and Linux due to the aforementioned platform differences, but for most cases it works okay on both platforms.