It isn't possible to temporarily resurrect objects safely in the Py3.15t limited API

Bug report

Bug description:

In Cython we do something like

Py_SET_REFCNT(o, Py_REFCNT(o) + 1);
// Run user implemented deallocation code
Py_SET_REFCNT(o, Py_REFCNT(o) - 1);

The reason for this is that we don't want any refcounting (e.g. of temps) within the user code to accidentally trigger a recursive call to dealloc (the user code really shouldn't resurrect the object and it's their own problem if they do, but it is reasonable for it to generate temporaries, which may well be out of their control anyway).

This turns out not to be thread-safe in the freethreaded build because it makes TryIncRef succeed. Outside the limited API it's possible to fix by manual access to the reference count, but obviously not inside the limited API.

It would be nice to have a way of to avoid this.

• Most convenient would be to properly access _PyObject_ResurrectStart and _PyObject_ResurrectEnd.
• The other thing that could work is some way to defer the deallocation until the next GC cycle (when I think any TryIncRefs would have fall out of scope anyway). I suspect I could manually arrange to do that, although it feels fragile, possibly relies on the GC being single-threaded, and which I haven't tested (so may not work...)

CPython versions tested on:

3.15

Operating systems tested on:

No response

Commencez par examiner la surface de la limited-API impliquée dans la résurrection du compteur de références et dans le comportement de TryIncRef en mode free-threaded décrit ici, puis comparez-la à _PyObject_ResurrectStart et _PyObject_ResurrectEnd ainsi qu’à l’issue #7769 de Cython. Le travail est considéré comme terminé lorsqu’un mécanisme défini et thread-safe de la limited-API évite une résurrection temporaire non sûre pendant le code de désallocation utilisateur.