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GeezerVison is showing github.com — gh-99574: Add Py_SETREF() to the limited C API by vstinner · Pull Request #99575 · python/cpython

gh-99574: Add Py_SETREF() to the limited C API #99575

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vstinner wants to merge 1 commit into python:main from vstinner:limited_setref

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gh-99574: Add Py_SETREF() to the limited C API #99575

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gh-99574: Add Py_SETREF() to the limited C API
vstinner Nov 18, 2022
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2 changes: 2 additions & 0 deletions 2 Doc/data/stable_abi.dat
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4 changes: 4 additions & 0 deletions 4 Doc/whatsnew/3.12.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -798,6 +798,10 @@ New Features
get a frame variable by its name.
(Contributed by Victor Stinner in :gh:`91248`.)

* Add :c:macro:`Py_SETREF` and :c:macro:`Py_XSETREF` macros to the limited C
API.
(Contributed by Victor Stinner in :gh:`99574`.)

Porting to Python 3.12
----------------------

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64 changes: 0 additions & 64 deletions 64 Include/cpython/object.h
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Original file line number Diff line number Diff line change
Expand Up @@ -305,70 +305,6 @@ _PyObject_GenericSetAttrWithDict(PyObject *, PyObject *,

PyAPI_FUNC(PyObject *) _PyObject_FunctionStr(PyObject *);

/* Safely decref `dst` and set `dst` to `src`.
*
* As in case of Py_CLEAR "the obvious" code can be deadly:
*
* Py_DECREF(dst);
* dst = src;
*
* The safe way is:
*
* Py_SETREF(dst, src);
*
* That arranges to set `dst` to `src` _before_ decref'ing, so that any code
* triggered as a side-effect of `dst` getting torn down no longer believes
* `dst` points to a valid object.
*
* Temporary variables are used to only evalutate macro arguments once and so
* avoid the duplication of side effects. _Py_TYPEOF() or memcpy() is used to
* avoid a miscompilation caused by type punning. See Py_CLEAR() comment for
* implementation details about type punning.
*
* The memcpy() implementation does not emit a compiler warning if 'src' has
* not the same type than 'src': any pointer type is accepted for 'src'.
*/
#ifdef _Py_TYPEOF
#define Py_SETREF(dst, src) \
do { \
_Py_TYPEOF(dst)* _tmp_dst_ptr = &(dst); \
_Py_TYPEOF(dst) _tmp_old_dst = (*_tmp_dst_ptr); \
*_tmp_dst_ptr = (src); \
Py_DECREF(_tmp_old_dst); \
} while (0)
#else
#define Py_SETREF(dst, src) \
do { \
PyObject **_tmp_dst_ptr = _Py_CAST(PyObject**, &(dst)); \
PyObject *_tmp_old_dst = (*_tmp_dst_ptr); \
PyObject *_tmp_src = _PyObject_CAST(src); \
memcpy(_tmp_dst_ptr, &_tmp_src, sizeof(PyObject*)); \
Py_DECREF(_tmp_old_dst); \
} while (0)
#endif

/* Py_XSETREF() is a variant of Py_SETREF() that uses Py_XDECREF() instead of
* Py_DECREF().
*/
#ifdef _Py_TYPEOF
#define Py_XSETREF(dst, src) \
do { \
_Py_TYPEOF(dst)* _tmp_dst_ptr = &(dst); \
_Py_TYPEOF(dst) _tmp_old_dst = (*_tmp_dst_ptr); \
*_tmp_dst_ptr = (src); \
Py_XDECREF(_tmp_old_dst); \
} while (0)
#else
#define Py_XSETREF(dst, src) \
do { \
PyObject **_tmp_dst_ptr = _Py_CAST(PyObject**, &(dst)); \
PyObject *_tmp_old_dst = (*_tmp_dst_ptr); \
PyObject *_tmp_src = _PyObject_CAST(src); \
memcpy(_tmp_dst_ptr, &_tmp_src, sizeof(PyObject*)); \
Py_XDECREF(_tmp_old_dst); \
} while (0)
#endif


PyAPI_DATA(PyTypeObject) _PyNone_Type;
PyAPI_DATA(PyTypeObject) _PyNotImplemented_Type;
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69 changes: 69 additions & 0 deletions 69 Include/object.h
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Original file line number Diff line number Diff line change
Expand Up @@ -637,6 +637,75 @@ static inline void Py_DECREF(PyObject *op)
#endif


#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x030C0000

/* Safely decref `dst` and set `dst` to `src`.
*
* As in case of Py_CLEAR "the obvious" code can be deadly:
*
* Py_DECREF(dst);
* dst = src;
*
* The safe way is:
*
* Py_SETREF(dst, src);
*
* That arranges to set `dst` to `src` _before_ decref'ing, so that any code
* triggered as a side-effect of `dst` getting torn down no longer believes
* `dst` points to a valid object.
*
* Temporary variables are used to only evalutate macro arguments once and so
* avoid the duplication of side effects. _Py_TYPEOF() or memcpy() is used to
* avoid a miscompilation caused by type punning. See Py_CLEAR() comment for
* implementation details about type punning.
*
* The memcpy() implementation does not emit a compiler warning if 'src' has
* not the same type than 'src': any pointer type is accepted for 'src'.
*/
#ifdef _Py_TYPEOF
#define Py_SETREF(dst, src) \
do { \
_Py_TYPEOF(dst)* _tmp_dst_ptr = &(dst); \
_Py_TYPEOF(dst) _tmp_old_dst = (*_tmp_dst_ptr); \
*_tmp_dst_ptr = (src); \
Py_DECREF(_tmp_old_dst); \
} while (0)
#else
#define Py_SETREF(dst, src) \
do { \
PyObject **_tmp_dst_ptr = _Py_CAST(PyObject**, &(dst)); \
PyObject *_tmp_old_dst = (*_tmp_dst_ptr); \
PyObject *_tmp_src = _PyObject_CAST(src); \
memcpy(_tmp_dst_ptr, &_tmp_src, sizeof(PyObject*)); \
Py_DECREF(_tmp_old_dst); \
} while (0)
#endif

/* Py_XSETREF() is a variant of Py_SETREF() that uses Py_XDECREF() instead of
* Py_DECREF().
*/
#ifdef _Py_TYPEOF
#define Py_XSETREF(dst, src) \
do { \
_Py_TYPEOF(dst)* _tmp_dst_ptr = &(dst); \
_Py_TYPEOF(dst) _tmp_old_dst = (*_tmp_dst_ptr); \
*_tmp_dst_ptr = (src); \
Py_XDECREF(_tmp_old_dst); \
} while (0)
#else
#define Py_XSETREF(dst, src) \
do { \
PyObject **_tmp_dst_ptr = _Py_CAST(PyObject**, &(dst)); \
PyObject *_tmp_old_dst = (*_tmp_dst_ptr); \
PyObject *_tmp_src = _PyObject_CAST(src); \
memcpy(_tmp_dst_ptr, &_tmp_src, sizeof(PyObject*)); \
Py_XDECREF(_tmp_old_dst); \
} while (0)
#endif

#endif // Py_LIMITED_API


/* Function to use in case the object pointer can be NULL: */
static inline void Py_XINCREF(PyObject *op)
{
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2 changes: 2 additions & 0 deletions 2 Misc/NEWS.d/next/C API/2022-11-18-13-22-31.gh-issue-99574.kmYSuk.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Add :c:macro:`Py_SETREF()` and :c:macro:`Py_XSETREF()` macros to the limited
C API. Patch by Victor Stinner.
5 changes: 5 additions & 0 deletions 5 Misc/stable_abi.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -2386,3 +2386,8 @@
added = '3.12' # Before 3.12, available in "structmember.h" w/o Py_ prefix
[const.Py_AUDIT_READ]
added = '3.12' # Before 3.12, available in "structmember.h"

[macro.Py_SETREF]
added = '3.12'
[macro.Py_XSETREF]
added = '3.12'
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