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gh-118789: Add PyUnstable_Object_ClearWeakRefsNoCallbacks #118807

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Merged
merged 6 commits into from
Jun 18, 2024
Merged

gh-118789: Add PyUnstable_Object_ClearWeakRefsNoCallbacks #118807

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f1fc2bc
gh-118789: Add `PyUnstable_Weakref_ClearWeakRefsExceptCallbacks`
colesbury May 8, 2024
9330f51
Adjust name and check _PyType_SUPPORTS_WEAKREFS
colesbury May 9, 2024
dc28627
Rename to PyUnstable_Object_ClearWeakRefsNoCallbacks
colesbury Jun 6, 2024
652c1c1
Add test for PyUnstable_Object_ClearWeakRefsNoCallbacks
encukou Jun 7, 2024
519a347
Add more context for when to use PyUnstable_Object_ClearWeakRefsNoCal…
colesbury Jun 17, 2024
29582a9
Merge branch 'main' into gh-118789-PyUnstable_Weakref_ClearWeakRefsEx…
colesbury Jun 17, 2024
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gh-118789: Add PyUnstable_Weakref_ClearWeakRefsExceptCallbacks 
This exposes `_PyWeakref_ClearWeakRefsExceptCallbacks` as an unstable
C-API function to provide a thread-safe mechanism for clearing weakrefs
without executing callbacks.

Some C-API extensions need to clear weakrefs without calling callbacks,
such as after running finalizers like we do in subtype_dealloc.
Previously they could use `_PyWeakref_ClearRef` on each weakref, but
that's not thread-safe in the free-threaded build.
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@colesbury
colesbury committed May 8, 2024
commit f1fc2bc0cb2db4d00e53eead73ffc5c72e2576af
7 changes: 7 additions & 0 deletions 7 Doc/c-api/weakref.rst
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Expand Up @@ -96,3 +96,10 @@ as much as it can.
This iterates through the weak references for *object* and calls callbacks
for those references which have one. It returns when all callbacks have
been attempted.


.. c:function:: void PyUnstable_Weakref_ClearWeakRefsExceptCallbacks(PyObject *object)

Clears the weakrefs for *object* without calling the callbacks.
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.. versionadded:: 3.13
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IMO it's too late for 3.13, we're past beta1.

Suggested change
.. versionadded:: 3.13
.. versionadded:: 3.14

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@Yhg1s - is it okay to make this function public in 3.13? From our discussion on Discord in May, it sounded like you were okay with this before the RC, but I'd like to make sure.

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Yes, considering the circumstances, this is reasonable to add in beta 3.

3 changes: 3 additions & 0 deletions 3 Include/cpython/weakrefobject.h
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Expand Up @@ -59,3 +59,6 @@ Py_DEPRECATED(3.13) static inline PyObject* PyWeakref_GET_OBJECT(PyObject *ref_o
return Py_None;
}
#define PyWeakref_GET_OBJECT(ref) PyWeakref_GET_OBJECT(_PyObject_CAST(ref))

// Clear weakrefs but do not call callbacks
PyAPI_FUNC(void) PyUnstable_Weakref_ClearWeakRefsExceptCallbacks(PyObject *obj);
2 changes: 2 additions & 0 deletions 2 Misc/NEWS.d/next/C API/2024-05-08-21-57-50.gh-issue-118789.Ni4UQx.rst
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@@ -0,0 +1,2 @@
Add :c:func:`PyUnstable_Weakref_ClearWeakRefsExceptCallbacks`, which clears
weakrefs without calling their callbacks.
6 changes: 6 additions & 0 deletions 6 Objects/weakrefobject.c
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Expand Up @@ -1090,6 +1090,12 @@ _PyWeakref_ClearWeakRefsExceptCallbacks(PyObject *obj)
UNLOCK_WEAKREFS(obj);
}

void
PyUnstable_Weakref_ClearWeakRefsExceptCallbacks(PyObject *obj)
{
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I suggest to check if _PyType_SUPPORTS_WEAKREFS(Py_TYPE(op)) and do nothing (return) if it's not the case.

_PyWeakref_ClearWeakRefsExceptCallbacks(obj);
}

int
_PyWeakref_IsDead(PyObject *weakref)
{
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