bpo-42972: Fully support GC for _winapi.Overlapped (GH-26381)

(cherry picked from commit 0fa282c) Co-authored-by: Ken Jin <28750310+Fidget-Spinner@users.noreply.github.com>
python · miss-islington · May 28, 2021 · May 28, 2021 · c807292f01d71cc6dc469aee9e76407c9d9ce05e
commit c807292f01d71cc6dc469aee9e76407c9d9ce05e
diff --git a/Modules/_winapi.c b/Modules/_winapi.c
@@ -112,6 +112,20 @@ typedef struct {
    Py_buffer write_buffer;
 } OverlappedObject;

+/*
+Note: tp_clear (overlapped_clear) is not implemented because it
+requires cancelling the IO operation if it's pending and the cancellation is
+quite complex and can fail (see: overlapped_dealloc).
+*/
+static int
+overlapped_traverse(OverlappedObject *self, visitproc visit, void *arg)
+{
+    Py_VISIT(self->read_buffer);
+    Py_VISIT(self->write_buffer.obj);
+    Py_VISIT(Py_TYPE(self));
+    return 0;
+}
+
 static void
 overlapped_dealloc(OverlappedObject *self)
 {
@@ -150,6 +164,7 @@ overlapped_dealloc(OverlappedObject *self)

    CloseHandle(self->overlapped.hEvent);
    SetLastError(err);
+    PyObject_GC_UnTrack(self);
    if (self->write_buffer.obj)
        PyBuffer_Release(&self->write_buffer);
    Py_CLEAR(self->read_buffer);
@@ -321,6 +336,7 @@ static PyMemberDef overlapped_members[] = {
 };

 static PyType_Slot winapi_overlapped_type_slots[] = {
+    {Py_tp_traverse, overlapped_traverse},
    {Py_tp_dealloc, overlapped_dealloc},
    {Py_tp_doc, "OVERLAPPED structure wrapper"},
    {Py_tp_methods, overlapped_methods},
@@ -331,15 +347,16 @@ static PyType_Slot winapi_overlapped_type_slots[] = {
 static PyType_Spec winapi_overlapped_type_spec = {
    .name = "_winapi.Overlapped",
    .basicsize = sizeof(OverlappedObject),
-    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
+    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION |
+              Py_TPFLAGS_HAVE_GC),
    .slots = winapi_overlapped_type_slots,
 };

 static OverlappedObject *
 new_overlapped(PyObject *module, HANDLE handle)
 {
    WinApiState *st = winapi_get_state(module);
-    OverlappedObject *self = PyObject_New(OverlappedObject, st->overlapped_type);
+    OverlappedObject *self = PyObject_GC_New(OverlappedObject, st->overlapped_type);
    if (!self)
        return NULL;

@@ -351,6 +368,8 @@ new_overlapped(PyObject *module, HANDLE handle)
    memset(&self->write_buffer, 0, sizeof(Py_buffer));
    /* Manual reset, initially non-signalled */
    self->overlapped.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
+
+    PyObject_GC_Track(self);
    return self;
 }

@@ -2043,12 +2062,37 @@ static PyModuleDef_Slot winapi_slots[] = {
    {0, NULL}
 };

+static int
+winapi_traverse(PyObject *module, visitproc visit, void *arg)
+{
+    WinApiState *st = winapi_get_state(module);
+    Py_VISIT(st->overlapped_type);
+    return 0;
+}
+
+static int
+winapi_clear(PyObject *module)
+{
+    WinApiState *st = winapi_get_state(module);
+    Py_CLEAR(st->overlapped_type);
+    return 0;
+}
+
+static void
+winapi_free(void *module)
+{
+    winapi_clear((PyObject *)module);
+}
+
 static struct PyModuleDef winapi_module = {
    PyModuleDef_HEAD_INIT,
    .m_name = "_winapi",
    .m_size = sizeof(WinApiState),
    .m_methods = winapi_functions,
    .m_slots = winapi_slots,
+    .m_traverse = winapi_traverse,
+    .m_clear = winapi_clear,
+    .m_free = winapi_free,
 };

 PyMODINIT_FUNC