Windows - Python 3.8+ raises "RuntimeError: Event Loop is closed" on exit.

Checklist

[ x] The bug is reproducible against the latest release and/or master.
[ x] There are no similar issues or pull requests to fix it yet.

Describe the bug

I get the following traceback when running the attached code

404
Exception ignored in: <function _ProactorBasePipeTransport.__del__ at 0x0000017C63D5E310>
Traceback (most recent call last):
  File "C:\Python\Python38\lib\asyncio\proactor_events.py", line 116, in __del__
    self.close()
  File "C:\Python\Python38\lib\asyncio\proactor_events.py", line 108, in close
    self._loop.call_soon(self._call_connection_lost, None)
  File "C:\Python\Python38\lib\asyncio\base_events.py", line 715, in call_soon
    self._check_closed()
  File "C:\Python\Python38\lib\asyncio\base_events.py", line 508, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed

To reproduce

async def testing():
    client = httpx.AsyncClient()
    response = await client.get("https://www.google.com/")
    await client.aclose()
    print(response.status_code)

async def main():
   await testing()

asyncio.run(main())

Inserting time.sleep(0.1) at the end of main() fixes it. Possibly due to the same reasons in the issues linked below.

Environment

Windows 10 64bit
Python version: 3.8.1
HTTPX version 0.12.1

Possibly the same as this and this

I assume this is yet another strange issue with asyncio’s stream.close() - it schedules the closing of the socket but it’s not guaranteed to be done once client.aclose finishes, which means the socket is actually deleted upon garbage collection, and by then I suppose the event loop is already closed... The sleep() call fixed this because it allows asyncio to execute the close callback before proceeding to shutdown the async environment.

See also #825 for more discussion on a possibly related issue.

Have you tried running this on Python 3.8.2?

Also: May well be specific to Window's Proactor event loop.

Yes, definitely looks like a Windows specific issue to me - the linked issues are for Windows too.

@florimondmanca

@florimondmanca , yes upgraded to 3.8.2 to check, the result is the same.

Can confirm this is an issue with the latest PyPi version of aiohttp and Python 3.8.2 on Windows.

Okay, thank you.

I personally don’t have a Windows machine so help with investigation and possible fixes would help.

Would we need to consider black magic such as aio-libs/aiohttp#1925 (comment)? How about aio-libs/aiohttp#3733?

FYI this is likely to be something to address on the HTTPCore side, as connection management and networking is done there. Might then be helpful to first come up with a minimal repro example using HTTPCore only?

It'd also be helpful to try switching to using SelectorEventLoop and let us know what the behaviour is like then... https://docs.python.org/3/library/asyncio-eventloop.html#event-loop-implementations (Or to try with Python 3.7 or earlier)

Python only switched the default event loop to proactor from 3.8 onwards. https://docs.python.org/3/library/asyncio-policy.html#asyncio.DefaultEventLoopPolicy

not sure there's a link and can't remember why now but in uvicorn we force the SelectorEventLoop to be the default for windows Le ven. 1 mai 2020 à 10:23 AM, Tom Christie <notifications@github.com> a écrit :

…

It'd also be helpful to try switching to using SelectorEventLoop and let us know what the behaviour is like then... https://docs.python.org/3/library/asyncio-eventloop.html#event-loop-implementations (Or to try with Python 3.7 or earlier) Python only switched the default event loop to proactor from 3.8 onwards. https://docs.python.org/3/library/asyncio-policy.html#asyncio.DefaultEventLoopPolicy — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#914 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAINSPTJI3OZEDU6VKCF2KLRPKBHTANCNFSM4MVRF2GQ> .

The workaround is to use the selector event loop like this:

import sys
import asyncio

if sys.version_info[0] == 3 and sys.version_info[1] >= 8 and sys.platform.startswith('win'):
    asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())

The following from the documentation will not resolve this issue (for some reason):

import asyncio
import selectors

selector = selectors.SelectSelector()
loop = asyncio.SelectorEventLoop(selector)
asyncio.set_event_loop(loop)

@Baysul

Thanks @Baysul.

This bug report looks like it is tracking the same issue.

Same as with #825 - Haven't looked into how awkward it is to do, but really I think we'd want to monkeypatch asyncio's socket unwrapping behaviour, so that we can reliably call .wait_closed(...) without it potentially hanging.

Can anyone on Windows, running Python 3.8+ confirm what currently happens when running this?...

import httpx
import asyncio

async def main():
    async with httpx.AsyncClient() as client:
        r = await client.get("https://login.microsoftonline.com/")
        print(r)

asyncio.run(main(), debug=True)

Trying to verify if we're still exposed to this issue. (I guess we are but 🤷‍♂️)

Windows 10
Python 3.10.2
NOTE: Problem occured before and after i installed httpx and httpcore
httpcore 0.14.7
httpx 0.22.0

Code gets the required data from BSCSCAN and then i get the Runtime Error.
The time.sleep(1) command didnt work.

PYTHON
import asyncio
from bscscan import BscScan

YOUR_API_KEY = "REDACTED"
CON_ADDR = "0xa38898a4ae982cb0131104a6746f77fa0da57aaa"
WAL_ADDR = "0x411709fd0cdd5f06ff6ef45b48aa0cb9842f01fc"

async def main():
async with BscScan(YOUR_API_KEY) as bsc:
print(await bsc.get_bnb_balance(address="0xa38898a4ae982cb0131104a6746f77fa0da57aaa")

if name == "main":
asyncio.run(main())

OUTPUT

I'm having the same issue on Windows 10. It does not matter what library I'm using.
If the loop is an ProactorEventLoop, then it is guaranteed that it will cause an exception if
there have been any network requests made which use SSL or sessions.

@pprovart

Okay - could you show me that absolute simplest possible example that reproduces this.

@pprovart's example here is pretty good - does it still replicate if you simplify it even further?...

import asyncio
import httpx

async def main():
    async with httpx.Client() as client:
        r = await client.get("https://www.example.com")
        print(r)

if name == "main":
    asyncio.run(main())

Also, does it replicate with both http and https URLs?

@Mennaruuk - Ah yup. Just looked though this thread and reminded myself of the comment here.

This is a bug in Python's stdlib with Windows. See: https://bugs.python.org/issue39232

One option here might be to check if the ProactorEventLoop is the default, and warn if it is.

when using async with httpx.AsyncClient() as client the transport should be closed correctly by anyio and not trigger the __del__ so this looks like an anyio bug

@pprovart

@pprovart is using aiohttp and not httpx https://github.com/pcko1/bscscan-python/blob/fcfc30cb7d1a4ff2a4f2de30606f35698675cbc7/bscscan/core/async_client.py#L32

This bug in the Python stdlib appears to have been fixed now in 3.11 (and possibly backported to 3.10?)

python/cpython#83413

Are any windows users here able to attempt replicating the original issue on the latest patch versions of Python 3.9, 3.10 and 3.12?

This bug in the Python stdlib appears to have been fixed now in 3.11 (and possibly backported to 3.10?)

python/cpython#83413

Are any windows users here able to attempt replicating the original issue on the latest patch versions of Python 3.9, 3.10 and 3.12?

I can test later today.

This problem also occurs on linux.

Exception ignored in: <function BaseSubprocessTransport.__del__ at 0x7f85c758ce50>
Traceback (most recent call last):
  File "/usr/lib/python3.8/asyncio/base_subprocess.py", line 126, in __del__
    self.close()
  File "/usr/lib/python3.8/asyncio/base_subprocess.py", line 104, in close
    proto.pipe.close()
  File "/usr/lib/python3.8/asyncio/unix_events.py", line 536, in close
    self._close(None)
  File "/usr/lib/python3.8/asyncio/unix_events.py", line 560, in _close
    self._loop.call_soon(self._call_connection_lost, exc)
  File "/usr/lib/python3.8/asyncio/base_events.py", line 711, in call_soon
    self._check_closed()
  File "/usr/lib/python3.8/asyncio/base_events.py", line 504, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed

This problem also occurs on linux.

Have you considered switching to recent version of python?

fix(outlook): Попытка исправить ошибку «Asyncio Event Loop is Closed»

V-0.28.1 Windows The error is still there

ERROR Task exception was never retrieved
future: <Task finished name='Task-288' coro=<AsyncClient.aclose() done, defined at \.venv\Lib\site-packages\httpx\_client.py:1978> exception=RuntimeError('Event loop is closed')>
Traceback (most recent call last):
  File "\.venv\Lib\site-packages\httpx\_client.py", line 1985, in aclose
    await self._transport.aclose()
  File "\.venv\Lib\site-packages\httpx\_transports\default.py", line 406, in aclose
    await self._pool.aclose()
  File "\.venv\Lib\site-packages\httpcore\_async\connection_pool.py", line 353, in aclose
    await self._close_connections(closing_connections)
  File "\.venv\Lib\site-packages\httpcore\_async\connection_pool.py", line 345, in _close_connections
    await connection.aclose()
  File "\.venv\Lib\site-packages\httpcore\_async\connection.py", line 173, in aclose
    await self._connection.aclose()
  File "\.venv\Lib\site-packages\httpcore\_async\http11.py", line 258, in aclose
    await self._network_stream.aclose()
  File "\.venv\Lib\site-packages\httpcore\_backends\anyio.py", line 53, in aclose
    await self._stream.aclose()
  File "\.venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 1314, in aclose
    self._transport.close()
  File "C:\Users\<user>\AppData\Roaming\uv\python\cpython-3.12.10-windows-x86_64-none\Lib\asyncio\proactor_events.py", line 109, in close
    self._loop.call_soon(self._call_connection_lost, None)
  File "C:\Users\<user>\AppData\Roaming\uv\python\cpython-3.12.10-windows-x86_64-none\Lib\asyncio\base_events.py", line 799, in call_soon
    self._check_closed()
  File "C:\Users\<user>\AppData\Roaming\uv\python\cpython-3.12.10-windows-x86_64-none\Lib\asyncio\base_events.py", line 545, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed

Navigation Menu

Repository navigation

Windows - Python 3.8+ raises "RuntimeError: Event Loop is closed" on exit. #914

Checklist

Describe the bug

To reproduce

Environment

21 remaining items

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Windows - Python 3.8+ raises "RuntimeError: Event Loop is closed" on exit. #914

Description

Checklist

Describe the bug

To reproduce

Environment

Activity

florimondmanca commented on Apr 30, 2020

lovelydinosaur commented on Apr 30, 2020

florimondmanca commented on Apr 30, 2020

rmawatson commented on Apr 30, 2020

Baysul commented on May 1, 2020

florimondmanca commented on May 1, 2020

lovelydinosaur commented on May 1, 2020

euri10 commented on May 1, 2020

Baysul commented on May 1, 2020

rmawatson commented on May 2, 2020

lovelydinosaur commented on May 6, 2020

lovelydinosaur commented on Aug 20, 2020

21 remaining items

pprovart commented on Feb 10, 2022

aabmets commented on Feb 24, 2022

lovelydinosaur commented on Feb 25, 2022

lovelydinosaur commented on Feb 25, 2022

graingert commented on Jun 18, 2022

graingert commented on Jun 18, 2022

lovelydinosaur commented on Dec 11, 2022

mbwmbw1337 commented on Dec 11, 2022

FANGOD commented on Jan 18, 2023

kpostekk commented on Jan 18, 2023

piscesvivian commented on Aug 1, 2025

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions