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gh-133931: Introduce _PyObject_XSetRefDelayed to replace Py_XSETREF #134377

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gh-133931: Introduce _PyObject_XSetRefDelayed to replace Py_XSETREF #134377

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09baa04
gh-133931: Introduce _PyObject_XSetRefDelayed to replace Py_XSETREF
corona10 May 20, 2025
1ee0825
fix
corona10 May 20, 2025
753df7a
Address code review
corona10 May 21, 2025
a168de0
fix
corona10 May 21, 2025
e7f6d01
fix issue
corona10 Jun 7, 2025
6287322
nit
corona10 Jun 7, 2025
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corona10 Jun 7, 2025
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12 changes: 12 additions & 0 deletions Include/internal/pycore_pymem.h
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Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,18 @@ static inline void _PyObject_XDecRefDelayed(PyObject *obj)
}
#endif

#ifdef Py_GIL_DISABLED
// This is the delayed-free equivalent of Py_XSETREF(), providing the same
// atomic reference assignment semantics but with deferred cleanup suitable
// for concurrent access patterns in free-threaded Python.
PyAPI_FUNC(void) _PyObject_XSetRefDelayed(PyObject **p_obj, PyObject *obj);
#else
static inline void _PyObject_XSetRefDelayed(PyObject **p_obj, PyObject *obj)
{
Py_XSETREF(*p_obj, obj);
}
#endif

// Periodically process delayed free requests.
extern void _PyMem_ProcessDelayed(PyThreadState *tstate);

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9 changes: 7 additions & 2 deletions Objects/genobject.c
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Expand Up @@ -10,6 +10,7 @@
#include "pycore_gc.h" // _PyGC_CLEAR_FINALIZED()
#include "pycore_genobject.h" // _PyGen_SetStopIterationValue()
#include "pycore_interpframe.h" // _PyFrame_GetCode()
#include "pycore_pymem.h" // _PyObject_XSetRefDelayed()
#include "pycore_modsupport.h" // _PyArg_CheckPositional()
#include "pycore_object.h" // _PyObject_GC_UNTRACK()
#include "pycore_opcode_utils.h" // RESUME_AFTER_YIELD_FROM
Expand Down Expand Up @@ -718,7 +719,9 @@ gen_set_name(PyObject *self, PyObject *value, void *Py_UNUSED(ignored))
"__name__ must be set to a string object");
return -1;
}
Py_XSETREF(op->gi_name, Py_NewRef(value));
Py_BEGIN_CRITICAL_SECTION(self);
_PyObject_XSetRefDelayed(&op->gi_name, Py_NewRef(value));
Py_END_CRITICAL_SECTION();
return 0;
}

Expand All @@ -740,7 +743,9 @@ gen_set_qualname(PyObject *self, PyObject *value, void *Py_UNUSED(ignored))
"__qualname__ must be set to a string object");
return -1;
}
Py_XSETREF(op->gi_qualname, Py_NewRef(value));
Py_BEGIN_CRITICAL_SECTION(self);
_PyObject_XSetRefDelayed(&op->gi_qualname, Py_NewRef(value));
Py_END_CRITICAL_SECTION();
return 0;
}

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18 changes: 18 additions & 0 deletions Objects/obmalloc.c
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Expand Up @@ -1231,6 +1231,24 @@ _PyObject_XDecRefDelayed(PyObject *ptr)
}
#endif

#ifdef Py_GIL_DISABLED
void
_PyObject_XSetRefDelayed(PyObject **ptr, PyObject *value)
{
PyObject *old = *ptr;
FT_ATOMIC_STORE_PTR_RELEASE(*ptr, value);
if (old == _Py_NULL) {
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Suggested change
if (old == _Py_NULL) {
if (old == NULL) {

_Py_NULL is only needed in headers

return;
}
if (!_Py_IsImmortal(old)) {
_PyObject_XDecRefDelayed(old);
}
else {
Py_DECREF(old);
}
}
#endif

static struct _mem_work_chunk *
work_queue_first(struct llist_node *head)
{
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8 changes: 1 addition & 7 deletions Objects/typeobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3967,13 +3967,7 @@ _PyObject_SetDict(PyObject *obj, PyObject *value)
return -1;
}
Py_BEGIN_CRITICAL_SECTION(obj);
PyObject *olddict = *dictptr;
FT_ATOMIC_STORE_PTR_RELEASE(*dictptr, Py_NewRef(value));
#ifdef Py_GIL_DISABLED
_PyObject_XDecRefDelayed(olddict);
#else
Py_XDECREF(olddict);
#endif
_PyObject_XSetRefDelayed(dictptr, Py_NewRef(value));
Py_END_CRITICAL_SECTION();
return 0;
}
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