Why does the asyncio's event loop suppress the KeyboardInterrupt on Windows?

Question

I have this really small test program which does nothing apart from a executing an asyncio event loop:

import asyncio
asyncio.get_event_loop().run_forever()

When I run this program on Linux and press Ctrl+C, the program will terminate correctly with a KeyboardInterrupt exception. On Windows pressing Ctrl+C does nothing (tested with Python 3.4.2). A simple inifinite loop with time.sleep() raises the KeyboardInterrupt correctly even on Windows:

import time
while True:
    time.sleep(3600)

Why does the asyncio's event loop suppress the KeyboardInterrupt on Windows?

Answer 1

This is a bug, sure.

See issue on python bug-tracker for the problem solving progress.

Answer 2

There is workaround for Windows. Run another corouting which wake up loop every second and allow loop to react on keyboard interrupt

Example with Echo server from asyncio doc

async def wakeup():
    while True:
        await asyncio.sleep(1)

loop = asyncio.get_event_loop()
coro = loop.create_server(EchoServerClientProtocol, '127.0.0.1', 8888)
server = loop.run_until_complete(coro)

# add wakeup HACK
loop.create_task(wakeup())

try:
    loop.run_forever()
except KeyboardInterrupt:
    pass

Answer 3

If you just want to exit the program and don't need to catch the KeyboardInterrupt, the signal module provides a simpler (and more efficient) workaround:

# This restores the default Ctrl+C signal handler, which just kills the process
import signal
signal.signal(signal.SIGINT, signal.SIG_DFL)

# Now the event loop is interruptable
import asyncio
asyncio.get_event_loop().run_forever()