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gh-139716: Use the same StackRef flagging scheme for immortals on FT build as on GIL build #141675

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gh-139716: Use the same StackRef flagging scheme for immortals on FT build as on GIL build #141675

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df6ea14
Another flag on immortal
efimov-mikhail Nov 17, 2025
fbda208
Use _Py_IMMORTAL_FLAGS == Py_TAG_REFCNT check on all builds
efimov-mikhail Nov 17, 2025
7b87fac
Use _PyGC_BITS_DEFERRED for all immortal objects
efimov-mikhail Nov 19, 2025
50e0fe3
Address review: add comment
efimov-mikhail Nov 19, 2025
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23 changes: 14 additions & 9 deletions Include/internal/pycore_stackref.h
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,13 @@ extern "C" {

#define Py_TAGGED_SHIFT 2

/* References to immortal objects always have their tag bit set to Py_TAG_REFCNT
* as they can (must) have their reclamation deferred */

#if _Py_IMMORTAL_FLAGS != Py_TAG_REFCNT
# error "_Py_IMMORTAL_FLAGS != Py_TAG_REFCNT"
#endif

#if !defined(Py_GIL_DISABLED) && defined(Py_STACKREF_DEBUG)

PyAPI_FUNC(PyObject *) _Py_stackref_get_object(_PyStackRef ref);
Expand Down Expand Up @@ -502,7 +509,12 @@ _PyStackRef_FromPyObjectSteal(PyObject *obj)
assert(obj != NULL);
// Make sure we don't take an already tagged value.
assert(((uintptr_t)obj & Py_TAG_BITS) == 0);
return (_PyStackRef){ .bits = (uintptr_t)obj };
if (_Py_IsImmortal(obj)) {
return (_PyStackRef){ .bits = (uintptr_t)obj | Py_TAG_DEFERRED };
}
else {
return (_PyStackRef){ .bits = (uintptr_t)obj };
}
}
# define PyStackRef_FromPyObjectSteal(obj) _PyStackRef_FromPyObjectSteal(_PyObject_CAST(obj))

Expand Down Expand Up @@ -542,7 +554,7 @@ PyStackRef_FromPyObjectNew(PyObject *obj)
// Make sure we don't take an already tagged value.
assert(((uintptr_t)obj & Py_TAG_BITS) == 0);
assert(obj != NULL);
if (_PyObject_HasDeferredRefcount(obj)) {
if (_PyObject_HasDeferredRefcount(obj) || _Py_IsImmortal(obj)) {
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@Fidget-Spinner Fidget-Spinner Nov 17, 2025

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I think we should just set immortal objects as having deferred refcount too in _Py_SetImmortal, that way this iwll just be a single check. Though it's been some time since I worked on FT so I don't know the implications of that (I think there should be none?)

return (_PyStackRef){ .bits = (uintptr_t)obj | Py_TAG_DEFERRED };
}
else {
Expand Down Expand Up @@ -631,13 +643,6 @@ PyStackRef_AsStrongReference(_PyStackRef stackref)

// With GIL

/* References to immortal objects always have their tag bit set to Py_TAG_REFCNT
* as they can (must) have their reclamation deferred */

#if _Py_IMMORTAL_FLAGS != Py_TAG_REFCNT
# error "_Py_IMMORTAL_FLAGS != Py_TAG_REFCNT"
#endif

#define BITS_TO_PTR(REF) ((PyObject *)((REF).bits))
#define BITS_TO_PTR_MASKED(REF) ((PyObject *)(((REF).bits) & (~Py_TAG_REFCNT)))

Expand Down
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