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Cannot cleanly kill a subprocess using high-level asyncio APIs #88050Description
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assignee = None
closed_at = None
created_at = <Date 2021-04-19.02:47:38.245>
labels = ['3.11', 'type-bug', 'expert-asyncio']
title = 'Cannot cleanly kill a subprocess using high-level asyncio APIs'
updated_at = <Date 2022-03-23.09:08:45.631>
user = 'https://bugs.python.org/rabraham' bugs.python.org fields:
activity = <Date 2022-03-23.09:08:45.631>
actor = 'kumaraditya'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['asyncio']
creation = <Date 2021-04-19.02:47:38.245>
creator = 'rabraham'
dependencies = []
files = ['49965']
hgrepos = []
issue_num = 43884
keywords = ['patch']
message_count = 6.0
messages = ['391349', '391350', '391369', '391379', '399937', '415859']
nosy_count = 6.0
nosy_names = ['asvetlov', 'yselivanov', 'rabraham', 'Dennis Sweeney', 'kumaraditya', 'skeggse']
pr_nums = ['31611', '32073']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue43884'
versions = ['Python 3.11'] Activityrabraham commented on Apr 19, 2021 MannequinAuthor More actions There doesn't appear to be a way to prematurely kill a subprocess using the high-level asyncio subprocess APIs (https://docs.python.org/3.9/library/asyncio-subprocess.html) without getting a traceback on exit.
On exit, the attached program writes the following to stderr:
$ python3.9 kill_subprocess.py Exception ignored in: <function BaseSubprocessTransport.__del__ at 0x1065f0dc0>
Traceback (most recent call last):
...
raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closedIf I uncomment # process._transport.close() or comment asyncio.sleep(1), the walkback disappears. (I get the same behavior in python 3.8. I haven't tried other python versions.) rabraham commented on Apr 19, 2021 MannequinAuthor More actions Reproducing the program here:
import asyncio
async def test():
process = await asyncio.create_subprocess_shell(
"sleep 2 && echo done",
stdout=asyncio.subprocess.PIPE,
)
await asyncio.sleep(1)
process.kill()
await process.wait()
# process._transport.close()
asyncio.run(test())Can I use the high-level API to kill a subprocess cleanly without having to access the protected member process._transport? Seems like an oversight perhaps? sweeneyde commented on Apr 19, 2021 Running kill_subprocess.py on Windows 10, I get these results:
Python 3.7.2 (tags/v3.7.2:9a3ffc0492)
- raises NotImplementedError in base_events.py, _make_subprocess_transport
Python 3.8.2 (tags/v3.8.2:7b3ab59)
- Success
Python 3.9.0 (tags/v3.9.0:9cf6752)
- Success
Python 3.10.0a6 (tags/v3.10.0a6:cc12888)
- Success
What is your OS? rabraham commented on Apr 19, 2021 MannequinAuthor More actions I see this on MacOS and Linux, but I suspect any Unix-like system would have the same behavior. skeggse commented on Aug 19, 2021 I'm also experiencing this, with virtually identical code, on macOS 10.15.7. The given fix (process._transport.close()) also works for me, so I'm just using that workaround for the time being. theo-brown commented on Feb 2, 2023 Is this meant to be fixed in 3.11+? gvanrossum commented on Feb 2, 2023 theo-brown commented on Feb 2, 2023 Which patch? Not in 3.11.0 as far as I can tell. gvanrossum commented on Feb 2, 2023 #32073 and a followup are present in 3.11.1. They may not be present in 3.11.0. gertvdijk commented on Apr 2, 2023 Hmm. I came here using Google while I'm on 3.11.2 already. This happens sometimes for me on a subprocess wrapped inside a task and stdin/stderr connected. It also only triggers when I am terminating a process myself, instead killing it or letting the loop killing it.
Found this when hitting random test failures on 3.11.2 and created the minimal reproducer below.
import asyncio
import logging
async def myfunc_inner() -> None:
subprocess_task = asyncio.create_task(
asyncio.create_subprocess_exec(
"sleep",
"10",
# seems to be relevant; unable to trigger without stdout/stderr connected
stdout=asyncio.subprocess.PIPE,
stderr=asyncio.subprocess.PIPE,
)
)
proc = await subprocess_task
try:
await asyncio.wait_for(proc.communicate(), timeout=0.02)
except (asyncio.TimeoutError, asyncio.CancelledError):
logging.info("Timeout on subprocess command, terminating.")
# unable to trigger with proc.kill() or without terminating it.
proc.terminate()
return
else:
logging.info(f"process exited with {proc.returncode}]")
# unable to trigger without nested task.
async def myfunc_outer() -> None:
await asyncio.wait_for(myfunc_inner(), timeout=1.0)
if __name__ == "__main__":
logging.basicConfig(level=logging.DEBUG)
loop = asyncio.get_event_loop_policy().new_event_loop()
loop.run_until_complete(myfunc_outer())
# This fixes it, but hides the underlying problem I think.
# loop.run_until_complete(asyncio.sleep(0.01))
loop.close()Running this in a shell loop 200 times, this gives ~ 1-10 failures per loop, looks random.
$ for i in `seq 1 200`; do python proctimeout.py; done
DEBUG:asyncio:Using selector: EpollSelector
Timeout on subprocess command, terminating.
DEBUG:asyncio:Using selector: EpollSelector
Timeout on subprocess command, terminating.
DEBUG:asyncio:Using selector: EpollSelector
Timeout on subprocess command, terminating.
Exception ignored in: <function BaseSubprocessTransport.__del__ at 0x7f5bff42a2a0>
Traceback (most recent call last):
File "/home/gert/.pyenv/versions/3.11.2/lib/python3.11/asyncio/base_subprocess.py", line 126, in __del__
self.close()
File "/home/gert/.pyenv/versions/3.11.2/lib/python3.11/asyncio/base_subprocess.py", line 104, in close
proto.pipe.close()
File "/home/gert/.pyenv/versions/3.11.2/lib/python3.11/asyncio/unix_events.py", line 558, in close
self._close(None)
File "/home/gert/.pyenv/versions/3.11.2/lib/python3.11/asyncio/unix_events.py", line 582, in _close
self._loop.call_soon(self._call_connection_lost, exc)
File "/home/gert/.pyenv/versions/3.11.2/lib/python3.11/asyncio/base_events.py", line 761, in call_soon
self._check_closed()
File "/home/gert/.pyenv/versions/3.11.2/lib/python3.11/asyncio/base_events.py", line 519, in _check_closed
raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed
DEBUG:asyncio:Using selector: EpollSelector
Timeout on subprocess command, terminating.
WARNING:asyncio:Loop <_UnixSelectorEventLoop running=False closed=True debug=False> that handles pid 419211 is closed
Exception ignored in: <function BaseSubprocessTransport.__del__ at 0x7f7dffc162a0>
Traceback (most recent call last):
File "/home/gert/.pyenv/versions/3.11.2/lib/python3.11/asyncio/base_subprocess.py", line 126, in __del__
self.close()
File "/home/gert/.pyenv/versions/3.11.2/lib/python3.11/asyncio/base_subprocess.py", line 104, in close
proto.pipe.close()
File "/home/gert/.pyenv/versions/3.11.2/lib/python3.11/asyncio/unix_events.py", line 558, in close
self._close(None)
File "/home/gert/.pyenv/versions/3.11.2/lib/python3.11/asyncio/unix_events.py", line 582, in _close
self._loop.call_soon(self._call_connection_lost, exc)
File "/home/gert/.pyenv/versions/3.11.2/lib/python3.11/asyncio/base_events.py", line 761, in call_soon
self._check_closed()
File "/home/gert/.pyenv/versions/3.11.2/lib/python3.11/asyncio/base_events.py", line 519, in _check_closed
raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed
DEBUG:asyncio:Using selector: EpollSelector
Timeout on subprocess command, terminating.
DEBUG:asyncio:Using selector: EpollSelector
Timeout on subprocess command, terminating.
DEBUG:asyncio:Using selector: EpollSelector
Timeout on subprocess command, terminating.
[...]Either removing proc.terminate() or replacing it with proc.kill() makes the traceback disappear. 🤷🏼
Also notice the (unrelated) error:
WARNING:asyncio:Loop <_UnixSelectorEventLoop running=False closed=True debug=False> that handles pid 419211 is closed
Further relevant system info: Python 3.11.2 (main, Mar 27 2023, 01:01:40) [GCC 12.2.1 20230201], built using Pyenv on Linux 6.2.9 (Arch, x86_64).
Am I doing something wrong here or hitting a corner case that's not tackled by this bugfix? Thanks! 🙏🏼 kumaraditya303 commented on Apr 3, 2023 You are missing await proc.wait() after terminating the process, adding that fixes it. Anyways this is not related to this fix so create a new issue if you still face the issue. gertvdijk commented on Apr 3, 2023
You are missing await proc.wait() after terminating the process, adding that fixes it.
Are you sure I should? It's also not included in Here’s an example of how asyncio can run a shell command and obtain its result, here: https://docs.python.org/3/library/asyncio-subprocess.html#
Note that I'm already awaiting the process result with communicate(). For wait() this comment (here) seems to indicate that as well I shouldn't:
Use the communicate() method when using pipes to avoid this condition.
Anyways this is not related to this fix so create a new issue if you still face the issue.
Sorry for the noise then, but to me it sounds exactly the same still. kumaraditya303 commented on Apr 3, 2023 You are wrapping proc.communicate() in wait_for so it gets cancelled before it had to chance to call self.wait(). See the source code. The docs are for directly awaiting the proc.communicate() which doesn't work in case of wait_for.
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