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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 All @@ -511,7 +523,7 @@ PyStackRef_IsHeapSafe(_PyStackRef stackref)
{
if (PyStackRef_IsDeferred(stackref)) {
PyObject *obj = PyStackRef_AsPyObjectBorrow(stackref);
return obj == NULL || _Py_IsImmortal(obj) || _PyObject_HasDeferredRefcount(obj);
return obj == NULL || _PyObject_HasDeferredRefcount(obj);
}
return true;
}
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
7 changes: 6 additions & 1 deletion Objects/object.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2675,6 +2675,12 @@ _Py_SetImmortalUntracked(PyObject *op)
assert(PyUnicode_CHECK_INTERNED(op) == SSTATE_INTERNED_IMMORTAL
|| PyUnicode_CHECK_INTERNED(op) == SSTATE_INTERNED_IMMORTAL_STATIC);
}
#endif
#ifdef Py_GIL_DISABLED
// We set these bits for all immortals, even static one, to simplify
// further checks on hot path. In fact, if _Py_IsImmortal(op) == 1,
// then _PyObject_HasDeferredRefcount(op) == 1.
_Py_atomic_or_uint8(&op->ob_gc_bits, _PyGC_BITS_DEFERRED);
#endif
// Check if already immortal to avoid degrading from static immortal to plain immortal
if (_Py_IsImmortal(op)) {
Expand All @@ -2684,7 +2690,6 @@ _Py_SetImmortalUntracked(PyObject *op)
op->ob_tid = _Py_UNOWNED_TID;
op->ob_ref_local = _Py_IMMORTAL_REFCNT_LOCAL;
op->ob_ref_shared = 0;
_Py_atomic_or_uint8(&op->ob_gc_bits, _PyGC_BITS_DEFERRED);
#elif SIZEOF_VOID_P > 4
op->ob_flags = _Py_IMMORTAL_FLAGS;
op->ob_refcnt = _Py_IMMORTAL_INITIAL_REFCNT;
Expand Down
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