ConnectionResetError on Python 3.8 for windows

[erezsh]

Using the simplest feature (prompt) fails with async exception.

After running the prompt, I kept pressing a,enter.

I'm using Windows 10, prompt_toolkit.__version__ = '2.0.10'

Python 3.8.0 (tags/v3.8.0:fa919fd, Oct 14 2019, 19:21:23) [MSC v.1916 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from prompt_toolkit import prompt
>>>
>>> while 1:
...     user_input = prompt('>')
...     print(user_input)
...
>a
a
>a
a
>a
a

Unhandled exception in event loop:
  File "C:\Python38\lib\asyncio\proactor_events.py", line 768, in _loop_self_reading
    f.result()  # may raise
  File "C:\Python38\lib\asyncio\windows_events.py", line 808, in _poll
    value = callback(transferred, key, ov)
  File "C:\Python38\lib\asyncio\windows_events.py", line 457, in finish_recv
    raise ConnectionResetError(*exc.args)

Exception [WinError 995] The I/O operation has been aborted because of either a thread exit or an application request
Press ENTER to continue...
>a
a
>a
a
>a
a
>a
a

Unhandled exception in event loop:
  File "C:\Python38\lib\asyncio\proactor_events.py", line 768, in _loop_self_reading
    f.result()  # may raise
  File "C:\Python38\lib\asyncio\windows_events.py", line 808, in _poll
    value = callback(transferred, key, ov)
  File "C:\Python38\lib\asyncio\windows_events.py", line 457, in finish_recv
    raise ConnectionResetError(*exc.args)

Exception [WinError 995] The I/O operation has been aborted because of either a thread exit or an application request
Press ENTER to continue...
>a
a
>a
a
>                                                                                                                       

[erezsh]

Note: This happens in both x32 and x64, but much less often in x64.

[jonathanslenders]

Thanks for reporting @erezsh!

I'm not sure what's going on, and wonder whether it's maybe even a bug in asyncio...

Can you see whether this is also the case for the SelectorEventLoop?

Run the following snippet before your code:

import asyncio
import selectors

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

[erezsh]

That seems to cure it!

What's going on here? Is it safe to use in my code?

[jonathanslenders]

Python 3.8 made the ProactorEventLoop the default on Windows. The code above tells Python to use a SelectorEventLoop instead, which is similar to Python 3.7 and before.

@vstinner: Could this be a bug in the ProactorEventLoop?

[vstinner]

I have no idea. If you think that it is a bug, write a producer and post it to bugs.python.org.

[jonathanslenders]

Issue opened at bugs.python.org: https://bugs.python.org/issue39010

[drskoolie]

Getting the same error when I run ijupyter in terminal.

Unhandled exception in event loop:
  File "c:\python38\lib\asyncio\proactor_events.py", line 768, in _loop_self_reading
    f.result()  # may raise
  File "c:\python38\lib\asyncio\windows_events.py", line 808, in _poll
    value = callback(transferred, key, ov)
  File "c:\python38\lib\asyncio\windows_events.py", line 457, in finish_recv
    raise ConnectionResetError(*exc.args)

Exception [WinError 995] The I/O operation has been aborted because of either a thread exit or an application request
Press ENTER to continue...

[musm]

Also getting this, do we have a workaround?

[jonathanslenders]

This was fixed in Python: python/cpython#22017
Best is to upgrade to a Python version that includes the fix, like Python 3.8.7.

Otherwise, the workaround is to make sure a SelectorEventLoop is used by asyncio. See for instance how it's done here: xonsh/xonsh#3430