PYTHON-3745 Add support for multiphase initialization

[blink1073]

No description provided.

[blink1073]

I scheduled all of the mod_wsgi tests to exercise subinterpreters.

[ShaneHarvey]

Should we set https://docs.python.org/3/c-api/module.html#c.Py_MOD_MULTIPLE_INTERPRETERS_SUPPORTED on 3.12+? IIUC that's what we support. The new work would be to set Py_MOD_PER_INTERPRETER_GIL_SUPPORTED.

Without Py_MOD_MULTIPLE_INTERPRETERS_SUPPORTED I think this change could break some users.

[blink1073]

Without Py_MOD_MULTIPLE_INTERPRETERS_SUPPORTED I think this change could break some users.

Fixed

[blink1073]

mod_wsgi 4.x Python 3.7 Ubuntu 22.04 is failing intermittently, both with and without the Py_MOD_MULTIPLE_INTERPRETERS_SUPPORTED block. mod_wsgi is a bit of a black box, should we skip that particular configuration and wait until we can more directly test multiple interpreters?

[ShaneHarvey]

mod_wsgi 4.x Python 3.7 Ubuntu 22.04 is failing intermittently

Is it also failing on main or only after the multiphase changes?

[blink1073]

After the multiphase changes

[ShaneHarvey]

I suggest we open a mod_wsgi issue to ask if multiphase init modules are supported: https://github.com/GrahamDumpleton/mod_wsgi

[blink1073]

It's the interpreter itself that defines compat as I understand it, the feature should be usable from Python 3.5. I propose we close this PR and restart when we can test directly against subinterpreters to see if there is an actual bug.

[ShaneHarvey]

I think it could be a bug in mod_wsgi because it has custom code to create subinterpreters. We'll also still need to keep the mod_wsgi tests even once we can test subinterpreters directly so I think we should try investigating the mod_wsgi bug now to avoid delaying this change.

[blink1073]

I'm going to have to backlog this for now until I finish OIDC work.

[ShaneHarvey]

Closing in favor of #1499