"Frank Millman" wrote in message news:n96kjr$mvl$1...@ger.gmane.org...
"Marko Rauhamaa" wrote in message
news:8737t5shhp....@elektro.pacujo.net...
> Actually, cancellation is specially supported in asyncio (<URL:
> https://docs.python.org/3/library/asyncio-task.html#asyncio.Task.cancel>)
> so this should do:
>
> async def background_task():
> while True:
> await perform_task()
> await asyncio.sleep(10)
>
That's exactly what I needed - thanks, Marko
async def background_task()
try:
while True:
await perform_task()
await asyncio.sleep(10)
except asyncio.CancelledError:
await perform_cleanup()
At startup -
task = asyncio.ensure_future(background_task())
At shutdown -
task.cancel()
await asyncio.wait([task])
Works perfectly - thanks again.
Alas, I spoke too soon.
I tried to simulate what would happen if the background task was busy with a
task when it was cancelled -
async def background_task()
try:
while True:
print('start')
time.sleep(2)
print('done')
await asyncio.sleep(10)
except asyncio.CancelledError:
print('cleanup')
print('DONE')
If I cancel after a pair of 'start/done' appear, the background task is in
the 'asyncio.sleep' stage. The words 'cleanup' and 'DONE' appear instantly,
and the program halts.
If I cancel after 'start', but before 'done', the background task is
executing a task. There is a delay of up to 2 seconds, then the words
'done', 'cleanup', and 'DONE' appear, but the program hangs. If I press
Ctrl+C, I get a traceback from the threading module -
line 1288, in _shutdown
t.join()
line 1054, in join
self._wait_for_tstate_lock()
line 1070, in _wait_for_tstate_lock
KeyboardInterrupt
So it is waiting for join() to complete. I will continue investigating, but
will report it here to see if anyone can come up with an
explanation/solution.
Thanks
Frank
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