Add a private API to defer automatic garbage collection

I would like to propose a private API that allows CPython internals to defer automatic garbage collection on the current thread without changing the interpreter-visible GC state.

Some CPython internals build large object graphs in a burst, where a collection triggered halfway through cannot reclaim anything from that operation and only traverses a half-built graph. Using PyGC_Disable() for this changes interpreter-wide state. Saving and restoring that state is racy in the free-threaded build, and it can also be observed or changed by user code in the GIL build.

What we want is something approximately like:

_PyGC_DeferAutomaticCollection(tstate);
/* Build a large object graph. */
_PyGC_ResumeAutomaticCollection(tstate);

This would be a private CPython API. It should be per-thread and nestable, keep allocation counters running, leave gc.isenabled() unchanged, and defer only automatic collection. Leaving the outermost scope would schedule a collection if one became due.

I think there are many possible cases in the stdlib and core that can benefit from this, and we currently do not have a safe tool for them. This can be implemented with a small nesting counter in _PyThreadStateImpl, checked by the allocation paths and _Py_RunGC(). This would allow these optimizations without changing user-visible GC state or introducing cross-thread races.

Linked PRs

• gh-154188

Commencez par examiner _PyThreadStateImpl, les chemins d’allocation et _Py_RunGC(), que la proposition identifie comme les points d’entrée pertinents. L’implémentation doit prendre en charge l’imbrication par thread, préserver les compteurs d’allocation et gc.isenabled(), différer uniquement la collecte automatique et planifier une collecte due lorsque la portée la plus externe reprend.