We have embedded Python in our application and we deinitialize/initialize the interpreter at some point of time. If a simple script with a thread that sleeps with asyncio.sleep is loaded before and after the re-initialization, then we get the following assertion in the second run of the python module:

"Assertion failed: Py_IS_TYPE(rl, &PyRunningLoopHolder_Type), file D:\a\1\s\Modules_asynciomodule.c, line 261"

Example to reproduce this crash: https://github.com/benjamin-sch/asyncio_crash_in_second_run

I guess the fix requires switching C Extension types from static to heap for _asyncio module.
It is possible for sure but requires a non-trivial amount of work.

We need a champion for the issue.

> "Assertion failed: Py_IS_TYPE(rl, &PyRunningLoopHolder_Type), file D:\a\1\s\Modules_asynciomodule.c, line 261"

The _asyncio extension uses static types and doesn't implement the multiphase initialization API. It doesn't work well with your "deinitialize/initialize the interpreter" use case.

The _asyncio extension should use heap types and the multiphase init API.

We were hitting the same issue in kodi, which uses embedded sub-interpreters to run python addons, after one of the addons was switched to asyncio.

The immediate cause of the assertion failure is a use-after-free issue from the running loop holder cache:

When the running loop holder is deallocated (which happens eg on interpreter shutdown) cached_running_holder holds a dangling pointer.

A subsequent call to get_running_loop() may then pick that up and boom.

While probably not a full fix for this issue I think it would be good to fix the use-after-free problem - there could be other code paths that lead to this situation. I've created a github pull request for that

New changeset 392a89835371baa0fc4bf79ae479abb80661f57d by Matthias Reichl in branch 'main':
 bpo-45262, asyncio: Fix cache of the running loop holder (GH-28796)
https://github.com/python/cpython/commit/392a89835371baa0fc4bf79ae479abb80661f57d

New changeset 87f0156a229e4cda92ad8e50645c5a71030caf7c by Miss Islington (bot) in branch '3.9':
bpo-45262, asyncio: Fix cache of the running loop holder (GH-28796)
https://github.com/python/cpython/commit/87f0156a229e4cda92ad8e50645c5a71030caf7c

Is Matthias Reichl's fix enough to use asyncio in a subinterpreter?

New changeset 6846d6712a0894f8e1a91716c11dd79f42864216 by Miss Islington (bot) in branch '3.10':
bpo-45262, asyncio: Fix cache of the running loop holder (GH-28796) (GH-28816)
https://github.com/python/cpython/commit/6846d6712a0894f8e1a91716c11dd79f42864216