8000 gh-128100: Atomic dict load in _PyObject_GenericGetAttrWithDict by wrongnull · Pull Request #128297 · python/cpython · GitHub
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gh-128100: Atomic dict load in _PyObject_GenericGetAttrWithDict #128297

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Merged
merged 4 commits into from
Dec 30, 2024
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gh-128100: Atomic dict load in _PyObject_GenericGetAttrWithDict #128297

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c8ccd02
Implement atomic load and critical section in C code
wrongnull Dec 26, 2024
3d0d584
Add tests
wrongnull Dec 26, 2024
7227e3e
Address the review
wrongnull Dec 27, 2024
b92759a
Remove test case.
colesbury Dec 30, 2024
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Implement atomic load and critical section in C code
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@wrongnull
wrongnull committed Dec 26, 2024
commit c8ccd02bbcec0ae12409efcd7beececaa436281a
6 changes: 6 additions & 0 deletions Objects/object.c
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Expand Up @@ -1715,10 +1715,16 @@ _PyObject_GenericGetAttrWithDict(PyObject *obj, PyObject *name,
dict = (PyObject *)_PyObject_GetManagedDict(obj);
}
else {
Py_BEGIN_CRITICAL_SECTION(obj);
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@ZeroIntensity ZeroIntensity Dec 27, 2024

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In general, we don't need to lock something if we're going to use one of the _Py_atomic APIs, and vice versa.

PyObject **dictptr = _PyObject_ComputedDictPointer(obj);
if (dictptr) {
#ifdef DISABLE_GIL
dict = (PyObject *)_Py_atomic_load_ptr(dictptr);
#else
dict = *dictptr;
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Here is where the atomic load should be. (And, as Sam said in the issue, we want _Py_atomic_load_ptr_acquire instead of plain old _Py_atomic_load_ptr.)

#endif
}
Py_END_CRITICAL_SECTION();
}
}
if (dict != NULL) {
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