mirror of https://github.com/python/cpython
gh-99952: [ctypes] fix refcount issues in from_param() result. (#100169)
Fixes a reference counting issue with `ctypes.Structure` when a `from_param()` method call is used and the structure size is larger than a C pointer `sizeof(void*)`. This problem existed for a very long time, but became more apparent in 3.8+ by change likely due to garbage collection cleanup timing changes.
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@ -266,6 +266,58 @@ class SimpleTypesTestCase(unittest.TestCase):
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self.assertRegex(repr(c_wchar_p.from_param('hihi')), r"^<cparam 'Z' \(0x[A-Fa-f0-9]+\)>$")
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self.assertRegex(repr(c_void_p.from_param(0x12)), r"^<cparam 'P' \(0x0*12\)>$")
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@test.support.cpython_only
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def test_from_param_result_refcount(self):
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# Issue #99952
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import _ctypes_test
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from ctypes import PyDLL, c_int, c_void_p, py_object, Structure
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class X(Structure):
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"""This struct size is <= sizeof(void*)."""
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_fields_ = [("a", c_void_p)]
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def __del__(self):
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trace.append(4)
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@classmethod
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def from_param(cls, value):
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trace.append(2)
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return cls()
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PyList_Append = PyDLL(_ctypes_test.__file__)._testfunc_pylist_append
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PyList_Append.restype = c_int
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PyList_Append.argtypes = [py_object, py_object, X]
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trace = []
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trace.append(1)
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PyList_Append(trace, 3, "dummy")
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trace.append(5)
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self.assertEqual(trace, [1, 2, 3, 4, 5])
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class Y(Structure):
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"""This struct size is > sizeof(void*)."""
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_fields_ = [("a", c_void_p), ("b", c_void_p)]
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def __del__(self):
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trace.append(4)
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@classmethod
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def from_param(cls, value):
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trace.append(2)
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return cls()
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PyList_Append = PyDLL(_ctypes_test.__file__)._testfunc_pylist_append
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PyList_Append.restype = c_int
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PyList_Append.argtypes = [py_object, py_object, Y]
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trace = []
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trace.append(1)
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PyList_Append(trace, 3, "dummy")
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trace.append(5)
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self.assertEqual(trace, [1, 2, 3, 4, 5])
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################################################################
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if __name__ == '__main__':
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@ -0,0 +1,2 @@
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Fix a reference undercounting issue in :class:`ctypes.Structure` with ``from_param()``
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results larger than a C pointer.
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@ -412,6 +412,7 @@ _ctypes_alloc_format_string_with_shape(int ndim, const Py_ssize_t *shape,
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typedef struct {
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PyObject_HEAD
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void *ptr;
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PyObject *keep; // If set, a reference to the original CDataObject.
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} StructParamObject;
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@ -419,6 +420,7 @@ static void
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StructParam_dealloc(PyObject *myself)
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{
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StructParamObject *self = (StructParamObject *)myself;
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Py_XDECREF(self->keep);
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PyMem_Free(self->ptr);
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Py_TYPE(self)->tp_free(myself);
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}
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@ -466,6 +468,7 @@ StructUnionType_paramfunc(CDataObject *self)
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StructParamObject *struct_param = (StructParamObject *)obj;
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struct_param->ptr = ptr;
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struct_param->keep = Py_NewRef(self);
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} else {
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ptr = self->b_ptr;
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obj = Py_NewRef(self);
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@ -1047,6 +1047,12 @@ EXPORT(long) _test_i38748_runCallback(_test_i38748_funcType callback, int a, int
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#endif
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EXPORT(int)
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_testfunc_pylist_append(PyObject *list, PyObject *item)
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{
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return PyList_Append(list, item);
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}
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static struct PyModuleDef_Slot _ctypes_test_slots[] = {
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{0, NULL}
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};
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