From e8752d7b80775ec2a348cd4bf38cbe26a4a07615 Mon Sep 17 00:00:00 2001 From: Sam Gross Date: Tue, 18 Jun 2024 09:57:23 -0400 Subject: [PATCH] gh-118789: Add `PyUnstable_Object_ClearWeakRefsNoCallbacks` (#118807) This exposes `PyUnstable_Object_ClearWeakRefsNoCallbacks` 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. Co-authored-by: Petr Viktorin --- Doc/c-api/weakref.rst | 16 +++++++++++ Include/cpython/object.h | 2 ++ Include/internal/pycore_weakref.h | 2 +- Lib/test/test_capi/test_object.py | 28 +++++++++++++++++++ ...-05-08-21-57-50.gh-issue-118789.Ni4UQx.rst | 2 ++ Modules/_testcapi/object.c | 8 ++++++ Objects/typeobject.c | 2 +- Objects/weakrefobject.c | 12 ++++++-- 8 files changed, 68 insertions(+), 4 deletions(-) create mode 100644 Misc/NEWS.d/next/C API/2024-05-08-21-57-50.gh-issue-118789.Ni4UQx.rst diff --git a/Doc/c-api/weakref.rst b/Doc/c-api/weakref.rst index ae069938390..8f233e16fb1 100644 --- a/Doc/c-api/weakref.rst +++ b/Doc/c-api/weakref.rst @@ -96,3 +96,19 @@ 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_Object_ClearWeakRefsNoCallbacks(PyObject *object) + + Clears the weakrefs for *object* without calling the callbacks. + + This function is called by the :c:member:`~PyTypeObject.tp_dealloc` handler + for types with finalizers (i.e., :meth:`~object.__del__`). The handler for + those objects first calls :c:func:`PyObject_ClearWeakRefs` to clear weakrefs + and call their callbacks, then the finalizer, and finally this function to + clear any weakrefs that may have been created by the finalizer. + + In most circumstances, it's more appropriate to use + :c:func:`PyObject_ClearWeakRefs` to clear weakrefs instead of this function. + + .. versionadded:: 3.13 diff --git a/Include/cpython/object.h b/Include/cpython/object.h index 0ab94e5e2a1..90cd7b54b34 100644 --- a/Include/cpython/object.h +++ b/Include/cpython/object.h @@ -288,6 +288,8 @@ PyAPI_FUNC(PyObject **) _PyObject_GetDictPtr(PyObject *); PyAPI_FUNC(void) PyObject_CallFinalizer(PyObject *); PyAPI_FUNC(int) PyObject_CallFinalizerFromDealloc(PyObject *); +PyAPI_FUNC(void) PyUnstable_Object_ClearWeakRefsNoCallbacks(PyObject *); + /* Same as PyObject_Generic{Get,Set}Attr, but passing the attributes dict as the last parameter. */ PyAPI_FUNC(PyObject *) diff --git a/Include/internal/pycore_weakref.h b/Include/internal/pycore_weakref.h index cc6c7ff9a9b..94aadb2c154 100644 --- a/Include/internal/pycore_weakref.h +++ b/Include/internal/pycore_weakref.h @@ -109,7 +109,7 @@ extern Py_ssize_t _PyWeakref_GetWeakrefCount(PyObject *obj); // Clear all the weak references to obj but leave their callbacks uncalled and // intact. -extern void _PyWeakref_ClearWeakRefsExceptCallbacks(PyObject *obj); +extern void _PyWeakref_ClearWeakRefsNoCallbacks(PyObject *obj); PyAPI_FUNC(int) _PyWeakref_IsDead(PyObject *weakref); diff --git a/Lib/test/test_capi/test_object.py b/Lib/test/test_capi/test_object.py index fa23bff4e98..cc9c9b688f0 100644 --- a/Lib/test/test_capi/test_object.py +++ b/Lib/test/test_capi/test_object.py @@ -103,5 +103,33 @@ def testPyObjectPrintOSError(self): with self.assertRaises(OSError): _testcapi.pyobject_print_os_error(output_filename) + +class ClearWeakRefsNoCallbacksTest(unittest.TestCase): + """Test PyUnstable_Object_ClearWeakRefsNoCallbacks""" + def test_ClearWeakRefsNoCallbacks(self): + """Ensure PyUnstable_Object_ClearWeakRefsNoCallbacks works""" + import weakref + import gc + class C: + pass + obj = C() + messages = [] + ref = weakref.ref(obj, lambda: messages.append("don't add this")) + self.assertIs(ref(), obj) + self.assertFalse(messages) + _testcapi.pyobject_clear_weakrefs_no_callbacks(obj) + self.assertIsNone(ref()) + gc.collect() + self.assertFalse(messages) + + def test_ClearWeakRefsNoCallbacks_no_weakref_support(self): + """Don't fail on objects that don't support weakrefs""" + import weakref + obj = object() + with self.assertRaises(TypeError): + ref = weakref.ref(obj) + _testcapi.pyobject_clear_weakrefs_no_callbacks(obj) + + if __name__ == "__main__": unittest.main() diff --git a/Misc/NEWS.d/next/C API/2024-05-08-21-57-50.gh-issue-118789.Ni4UQx.rst b/Misc/NEWS.d/next/C API/2024-05-08-21-57-50.gh-issue-118789.Ni4UQx.rst new file mode 100644 index 00000000000..32a9ec6d071 --- /dev/null +++ b/Misc/NEWS.d/next/C API/2024-05-08-21-57-50.gh-issue-118789.Ni4UQx.rst @@ -0,0 +1,2 @@ +Add :c:func:`PyUnstable_Object_ClearWeakRefsNoCallbacks`, which clears +weakrefs without calling their callbacks. diff --git a/Modules/_testcapi/object.c b/Modules/_testcapi/object.c index 8dd34cf4fc4..1c76e766a79 100644 --- a/Modules/_testcapi/object.c +++ b/Modules/_testcapi/object.c @@ -117,11 +117,19 @@ pyobject_print_os_error(PyObject *self, PyObject *args) Py_RETURN_NONE; } +static PyObject * +pyobject_clear_weakrefs_no_callbacks(PyObject *self, PyObject *obj) +{ + PyUnstable_Object_ClearWeakRefsNoCallbacks(obj); + Py_RETURN_NONE; +} + static PyMethodDef test_methods[] = { {"call_pyobject_print", call_pyobject_print, METH_VARARGS}, {"pyobject_print_null", pyobject_print_null, METH_VARARGS}, {"pyobject_print_noref_object", pyobject_print_noref_object, METH_VARARGS}, {"pyobject_print_os_error", pyobject_print_os_error, METH_VARARGS}, + {"pyobject_clear_weakrefs_no_callbacks", pyobject_clear_weakrefs_no_callbacks, METH_O}, {NULL}, }; diff --git a/Objects/typeobject.c b/Objects/typeobject.c index a380e74b07d..0dcf1d399d9 100644 --- a/Objects/typeobject.c +++ b/Objects/typeobject.c @@ -2533,7 +2533,7 @@ subtype_dealloc(PyObject *self) finalizers since they might rely on part of the object being finalized that has already been destroyed. */ if (type->tp_weaklistoffset && !base->tp_weaklistoffset) { - _PyWeakref_ClearWeakRefsExceptCallbacks(self); + _PyWeakref_ClearWeakRefsNoCallbacks(self); } } diff --git a/Objects/weakrefobject.c b/Objects/weakrefobject.c index 3b027e1b518..0fcd37d949b 100644 --- a/Objects/weakrefobject.c +++ b/Objects/weakrefobject.c @@ -1016,7 +1016,7 @@ PyObject_ClearWeakRefs(PyObject *object) PyObject *exc = PyErr_GetRaisedException(); PyObject *tuple = PyTuple_New(num_weakrefs * 2); if (tuple == NULL) { - _PyWeakref_ClearWeakRefsExceptCallbacks(object); + _PyWeakref_ClearWeakRefsNoCallbacks(object); PyErr_WriteUnraisable(NULL); PyErr_SetRaisedException(exc); return; @@ -1057,6 +1057,14 @@ PyObject_ClearWeakRefs(PyObject *object) PyErr_SetRaisedException(exc); } +void +PyUnstable_Object_ClearWeakRefsNoCallbacks(PyObject *obj) +{ + if (_PyType_SUPPORTS_WEAKREFS(Py_TYPE(obj))) { + _PyWeakref_ClearWeakRefsNoCallbacks(obj); + } +} + /* This function is called by _PyStaticType_Dealloc() to clear weak references. * * This is called at the end of runtime finalization, so we can just @@ -1076,7 +1084,7 @@ _PyStaticType_ClearWeakRefs(PyInterpreterState *interp, PyTypeObject *type) } void -_PyWeakref_ClearWeakRefsExceptCallbacks(PyObject *obj) +_PyWeakref_ClearWeakRefsNoCallbacks(PyObject *obj) { /* Modeled after GET_WEAKREFS_LISTPTR().