ResourceWarning: unclosed event loop about pytest-asyncio

[graingert]

@seifertm currently I'm trying to remove the policy system and get/set event loop in favour of loop_factory so this becomes a non-issue.

I think to fix this instead of using _provide_clean_event_loop you should call set_event_loop_policy(None) so asyncio.get_event_loop() returns to its original behaviour

[graingert]

full demo here kevin1024/vcrpy@d009336

more minimal reproducer here https://github.com/graingert/asyncio_unclosed_loop

[graingert]

I repeated this with e1415c1

[phillipuniverse]

I have the same issue in versions 0.22.0+, including 0.23.0a0.

I first spent a ton of time trying to hunt down a new ResourceWarning I seemingly randomly started getting in my tests (maybe due to the more tests I added and thus more time to fail with the resource warning, unsure):

>               warnings.warn(pytest.PytestUnraisableExceptionWarning(msg))
E               pytest.PytestUnraisableExceptionWarning: Exception ignored in: <socket.socket fd=-1, family=1, type=1, proto=0>
E               
E               Traceback (most recent call last):
E                 File "/Users/phillip/.pyenv/versions/3.11.6/lib/python3.11/json/decoder.py", line 353, in raw_decode
E                   obj, end = self.scan_once(s, idx)
E                              ^^^^^^^^^^^^^^^^^^^^^^
E               ResourceWarning: unclosed <socket.socket fd=13, family=1, type=1, proto=0>

I couldn't for the life of me figure out where I had an unclosed socket. So I finally admitted defeat and silenced the ResourceWarning, only to have this next error happen:

>               warnings.warn(pytest.PytestUnraisableExceptionWarning(msg))
E               pytest.PytestUnraisableExceptionWarning: Exception ignored in: <function BaseEventLoop.__del__ at 0x104bed760>
E               
E               Traceback (most recent call last):
E                 File "/Users/phillip/.pyenv/versions/3.11.6/lib/python3.11/asyncio/base_events.py", line 692, in __del__
E                   _warn(f"unclosed event loop {self!r}", ResourceWarning, source=self)
E               ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=False>

The results seemed to change depending on how many tests I was running in my test suite.

Downgrading to 0.21.1 fixed both problems.

[seifertm]

Thanks for the report! I can reproduce the issue with pytest-asyncio v0.23.2. I can also reproduce it with pytest-asyncio v0.21.1, though:

$ python -X dev -m pytest --setup-show
===== test session starts =====
platform linux -- Python 3.12.1, pytest-7.4.3, pluggy-1.3.0
rootdir: /tmp/tst
plugins: asyncio-0.21.1
asyncio: mode=Mode.STRICT
collected 2 items                                                                                                                   

test_a.py 
        SETUP    F event_loop
        SETUP    F demo (fixtures used: event_loop)
        test_a.py::test_aiohttp_test_client_json (fixtures used: demo, event_loop, request).
        TEARDOWN F demo
        TEARDOWN F event_loop
        test_a.py::test_redirect.

===== warnings summary =====test_a.py::test_redirect
  /usr/lib/python3.12/asyncio/base_events.py:723: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
    _warn(f"unclosed event loop {self!r}", ResourceWarning, source=self)
  Enable tracemalloc to get traceback where the object was allocated.
  See https://docs.pytest.org/en/stable/how-to/capture-warnings.html#resource-warnings for more info.

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
===== 2 passed, 1 warning in 0.02s =====

This means it's probably not directly related to the v0.23 release.

Based on the console output above, my current understanding is that pytest(-asyncio) runs the async test normally. When the event_loop fixture is torn down, a fixture finalizer creates a new event loop to prevent subsequent non-async tests from having to deal with a closed loop:

pytest-asyncio/pytest_asyncio/plugin.py

Lines 824 to 833 in b614c77

	def _provide_clean_event_loop() -> None:
	# At this point, the event loop for the current thread is closed.
	# When a user calls asyncio.get_event_loop(), they will get a closed loop.
	# In order to avoid this side effect from pytest-asyncio, we need to replace
	# the current loop with a fresh one.
	# Note that we cannot set the loop to None, because get_event_loop only creates
	# a new loop, when set_event_loop has not been called.
	policy = asyncio.get_event_loop_policy()
	new_loop = policy.new_event_loop()
	policy.set_event_loop(new_loop)

When the sync test calls asyncio.run, the loop created by the fixture finalizer is not closed by the asyncio Runner. I very recently encountered the same problem in a different issue.

@graingert I'm aware you're involved in upstream asyncio development. Do you think it's worth filing an enhancement issue for asyncio.run (or rather asyncio.Runner) to close any existing loop before setting a new loop?

@phillipuniverse If you don't use asyncio.run, it's possible that your issue has a separate cause. I can help more, if you provide a reproducer for you specific issue.