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gh-98724: Fix Py_CLEAR() macro side effects (#99100)

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The Py_CLEAR(), Py_SETREF() and Py_XSETREF() macros now only evaluate
their argument once. If an argument has side effects, these side
effects are no longer duplicated.

Add test_py_clear() and test_py_setref() unit tests to _testcapi.
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Victor Stinner 2022-11-09 14:06:36 +01:00 • committed by GitHub
parent 0124b5dd28
commit c03e05c2e7
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6 changed files with 175 additions and 29 deletions
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19
Include/object.h
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@ -598,16 +598,21 @@ static inline void Py_DECREF(PyObject *op)
* one of those can't cause problems -- but in part that relies on that
* Python integers aren't currently weakly referencable. Best practice is
* to use Py_CLEAR() even if you can't think of a reason for why you need to.
*
* gh-98724: Use the _py_tmp_ptr variable to evaluate the macro argument
* exactly once, to prevent the duplication of side effects in this macro.
*/
#define Py_CLEAR(op) \
do { \
PyObject *_py_tmp = _PyObject_CAST(op); \
if (_py_tmp != NULL) { \
(op) = NULL; \
Py_DECREF(_py_tmp); \
} \
#define Py_CLEAR(op) \
do { \
PyObject **_py_tmp_ptr = _Py_CAST(PyObject**, &(op)); \
if (*_py_tmp_ptr != NULL) { \
PyObject* _py_tmp = (*_py_tmp_ptr); \
*_py_tmp_ptr = NULL; \
Py_DECREF(_py_tmp); \
} \
} while (0)
/* Function to use in case the object pointer can be NULL: */
static inline void Py_XINCREF(PyObject *op)
{