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.
This commit is contained in:
Yukihiro Nakadaira 2023-01-26 17:28:34 +09:00 committed by GitHub
parent f5ad63f79a
commit dfad678d70
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GPG Key ID: 4AEE18F83AFDEB23
4 changed files with 63 additions and 0 deletions

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@ -266,6 +266,58 @@ class SimpleTypesTestCase(unittest.TestCase):
self.assertRegex(repr(c_wchar_p.from_param('hihi')), r"^<cparam 'Z' \(0x[A-Fa-f0-9]+\)>$")
self.assertRegex(repr(c_void_p.from_param(0x12)), r"^<cparam 'P' \(0x0*12\)>$")
@test.support.cpython_only
def test_from_param_result_refcount(self):
# Issue #99952
import _ctypes_test
from ctypes import PyDLL, c_int, c_void_p, py_object, Structure
class X(Structure):
"""This struct size is <= sizeof(void*)."""
_fields_ = [("a", c_void_p)]
def __del__(self):
trace.append(4)
@classmethod
def from_param(cls, value):
trace.append(2)
return cls()
PyList_Append = PyDLL(_ctypes_test.__file__)._testfunc_pylist_append
PyList_Append.restype = c_int
PyList_Append.argtypes = [py_object, py_object, X]
trace = []
trace.append(1)
PyList_Append(trace, 3, "dummy")
trace.append(5)
self.assertEqual(trace, [1, 2, 3, 4, 5])
class Y(Structure):
"""This struct size is > sizeof(void*)."""
_fields_ = [("a", c_void_p), ("b", c_void_p)]
def __del__(self):
trace.append(4)
@classmethod
def from_param(cls, value):
trace.append(2)
return cls()
PyList_Append = PyDLL(_ctypes_test.__file__)._testfunc_pylist_append
PyList_Append.restype = c_int
PyList_Append.argtypes = [py_object, py_object, Y]
trace = []
trace.append(1)
PyList_Append(trace, 3, "dummy")
trace.append(5)
self.assertEqual(trace, [1, 2, 3, 4, 5])
################################################################
if __name__ == '__main__':

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@ -0,0 +1,2 @@
Fix a reference undercounting issue in :class:`ctypes.Structure` with ``from_param()``
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,
typedef struct {
PyObject_HEAD
void *ptr;
PyObject *keep; // If set, a reference to the original CDataObject.
} StructParamObject;
@ -419,6 +420,7 @@ static void
StructParam_dealloc(PyObject *myself)
{
StructParamObject *self = (StructParamObject *)myself;
Py_XDECREF(self->keep);
PyMem_Free(self->ptr);
Py_TYPE(self)->tp_free(myself);
}
@ -466,6 +468,7 @@ StructUnionType_paramfunc(CDataObject *self)
StructParamObject *struct_param = (StructParamObject *)obj;
struct_param->ptr = ptr;
struct_param->keep = Py_NewRef(self);
} else {
ptr = self->b_ptr;
obj = Py_NewRef(self);

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@ -1047,6 +1047,12 @@ EXPORT(long) _test_i38748_runCallback(_test_i38748_funcType callback, int a, int
#endif
EXPORT(int)
_testfunc_pylist_append(PyObject *list, PyObject *item)
{
return PyList_Append(list, item);
}
static struct PyModuleDef_Slot _ctypes_test_slots[] = {
{0, NULL}
};