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Merged
vstinner merged 6 commits into from
May 28, 2021
Merged

bpo-42972: Fully support GC for _winapi.Overlapped #26381

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0fa0217
tp_traverse for _winapi.Overlapped
Fidget-Spinner May 26, 2021
9f3ca36
GC track the object
Fidget-Spinner May 26, 2021
96f0d0e
move untrack down to a safer place
Fidget-Spinner May 26, 2021
0493de0
add module m_traverse, clear, free - fully implement the GC protocol …
Fidget-Spinner May 26, 2021
fc3e774
static int -> static void
Fidget-Spinner May 26, 2021
78113cc
Apply victor's suggestions
Fidget-Spinner May 27, 2021
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48 changes: 46 additions & 2 deletions Modules/_winapi.c
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Original file line numberDiff line numberDiff line change
Expand Up@@ -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)
{
Expand DownExpand Up@@ -150,6 +164,7 @@ overlapped_dealloc(OverlappedObject *self)

CloseHandle(self->overlapped.hEvent);
SetLastError(err);
PyObject_GC_UnTrack(self);
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@vstinnervstinnerMay 27, 2021

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I would prefer to start by untracking the GC, at the start to the dealloc function.

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@Fidget-SpinnerFidget-SpinnerMay 27, 2021

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I initially did that, but a concern was brought up here which I think makes sense #26381 (comment).

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@vstinnervstinnerMay 27, 2021

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If tp_dealloc returns without clearing the object, IMO it's better to remove it from the GC. It's better to hide this badly broken Python object. I suggest to start by untracking and explain that it's a deliberate choice to untrack even if we hit the worst case scenario of "return" below.

Note: IMO this code should be removed, Windows XP is no longer supported, but it should be done in a separated change.

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@Fidget-SpinnerFidget-SpinnerMay 28, 2021

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Sorry, I just introduced a regression with this, seems like there's a race condition with the GC and the IO operation somewhere.

> python_d.exe -m test test_httplib -m test_local_bad_hostname ...\cpython\Modules\gcmodule.c:446: update_refs: Assertion "gc_get_refs(gc) != 0" failed Enable tracemalloc to get the memory block allocation traceback object address : 000002DADE2A99D0 object refcount : 0 object type : 000002DADDF72F60 object type name: _winapi.Overlapped object repr : <refcnt 0 at 000002DADE2A99D0> Fatal Python error: _PyObject_AssertFailed: _PyObject_AssertFailed Python runtime state: initialized

It seems that placing the PyObject_GC_UnTrack at the top actually fixes it...

if (self->write_buffer.obj)
PyBuffer_Release(&self->write_buffer);
Py_CLEAR(self->read_buffer);
Expand DownExpand Up@@ -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},
Expand All@@ -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;

Expand All@@ -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;
}

Expand DownExpand Up@@ -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
Expand Down