GeezerVison

… Consistently (pythongh-109921)

The existence of background threads running on a subinterpreter was preventing interpreters from getting properly destroyed, as well as impacting the ability to run the interpreter again. It also affected how we wait for non-daemon threads to finish.

We add PyInterpreterState.threads.main, with some internal C-API functions.

(cherry-picked from commit 1dd9dee)

…ta (pythongh-109556)

This fixes some crashes in the _xxinterpchannels module, due to a race between interpreters.
(cherry picked from commit fd7e08a)

Co-authored-by: Eric Snow <[email protected]>

…-109994)

This change makes sure sys.path[0] is set properly for subinterpreters.  Before, it wasn't getting set at all.

This change does not address the broader concerns from pythongh-109853.

(cherry-picked from commit a040a32)

…eters, When Necessary (pythongh-110245)

In a few places we switch to another interpreter without knowing if it has a thread state associated with the current thread.  For the main interpreter there wasn't much of a problem, but for subinterpreters we were *mostly* okay re-using the tstate created with the interpreter (located via PyInterpreterState_ThreadHead()).  There was a good chance that tstate wasn't actually in use by another thread.

However, there are no guarantees of that.  Furthermore, re-using an already used tstate is currently fragile.  To address this, now we create a new thread state in each of those places and use it.

One consequence of this change is that PyInterpreterState_ThreadHead() may not return NULL (though that won't happen for the main interpreter).

(cherry-picked from commit f5198b0)