gh-99952: [ctypes] fix refcount issues in from_param() result.

Author: ynkdir

Lib/test/test_ctypes/test_parameters.py

@@ -1,3 +1,4 @@
+import sys
 import unittest
 from test.test_ctypes import need_symbol
 import test.support
@@ -243,6 +244,58 @@ def test_parameter_repr(self):
         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
+    @unittest.skipUnless(sys.platform == "win32", 'Windows-specific test')
+    def test_from_param_result_refcount(self):
+        # Issue #99952
+        import sys
+        import _ctypes_test
+        from ctypes import PyDLL, c_int, c_void_p, py_object, Structure
+
+        class X(Structure):
+            _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("python", handle=sys.dllhandle).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):
+            _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("python", handle=sys.dllhandle).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__':

Modules/_ctypes/_ctypes.c

@@ -412,13 +412,15 @@ _ctypes_alloc_format_string_with_shape(int ndim, const Py_ssize_t *shape,
 typedef struct {
     PyObject_HEAD
     void *ptr;
+    PyObject *keep;
 } StructParamObject;
 
 
 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);