Why does this Python async script never finish? -


i created mcve example of larger code base working on, things funky way of doing things, minimal versions, not makes sense far why doing way. know work-arounds, , @ point curious why seeing behaviour.

i have following script has async function waits future. script intercepts signal set future result:

import asyncio import time import signal  f = asyncio.future() loop = asyncio.get_event_loop()  async def wait_till_signal():     await f  def send_stop():     print('stopping', time.time())     f.set_result(true)     print('sent')     print(f.result())  def handle_signal(s, a):     print('sending stop', time.time())     send_stop()  signal.signal(signal.sigint, handle_signal)  loop.run_until_complete(wait_till_signal())

this script correctly gets interrupt, , appears set future correctly, reason script never terminates.

to reproduce you, run script, hit ctrl+c. reason never stops.

now here gets weird. if add following top of script (after defining loop), script stops fine.

async def do_nothing_useful():      in range(30):          await asyncio.sleep(1)  loop.create_task(do_nothing_useful())

why coroutine not getting future in first case, gets correctly in second case?

also, weird thing if set send_stop function async, , add task, never gets called. (this follows same behaviour above. if do_nothing_useful() function on loop, works fine, without it, doesnt)

here version send_stop never called:

import asyncio import time import signal  f = asyncio.future()  async def wait_till_signal():     await f  async def send_stop():     # async because trying try out crazy things     print('stopping', time.time())     f.set_result(true)     print('sent')     print(f.result())   def handle_signal(s, a):     print('sending stop', time.time())     loop.create_task(send_stop())   signal.signal(signal.sigint, handle_signal)  loop = asyncio.get_event_loop() loop.run_until_complete(wait_till_signal()) print('done')

and script never prints stopping.

i have tried on python 3.5.3 , 3.6 on linux

the correct method add signal handler wakes loop using loop.add_signal_handler. make sure select() wakes handle signal.


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