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gh-116946: fully implement GC protocol for _tkinter.Tk{app,tt}Object #138331

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Merged
merged 11 commits into from
Sep 11, 2025
Merged

gh-116946: fully implement GC protocol for _tkinter.Tk{app,tt}Object #138331

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84f832f
fully implement GC protocol for `_tkinter` objects
picnixz Sep 1, 2025
a9c01ef
make _tkinter.Tcl_Obj immutable instead of supporting full GC
picnixz Sep 2, 2025
dbb343f
revert changes to `_tkinter.Tcl_Obj`; they will be made later
picnixz Sep 6, 2025
9eb9f47
Merge branch 'main' into fix/gc/tkinter-heap-types-116946
picnixz Sep 6, 2025
8e80641
add tp_clear for visited objects
picnixz Sep 6, 2025
833a85e
use the correct slot...
picnixz Sep 6, 2025
022d71e
revert the revert
picnixz Sep 6, 2025
168fe43
keep the necessary bits
picnixz Sep 6, 2025
5e5f698
remove warnings
picnixz Sep 6, 2025
35915b0
reduce the diff a bit
picnixz Sep 11, 2025
ba9c809
Merge remote-tracking branch 'upstream/main' into fix/gc/tkinter-heap…
picnixz Sep 11, 2025
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95 changes: 72 additions & 23 deletions Modules/_tkinter.c
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Original file line number Diff line number Diff line change
Expand Up @@ -589,10 +589,14 @@ Tkapp_New(const char *screenName, const char *className,
int interactive, int wantobjects, int wantTk, int sync,
const char *use)
{
PyTypeObject *type;
TkappObject *v;
char *argv0;

v = PyObject_New(TkappObject, (PyTypeObject *) Tkapp_Type);
type = (PyTypeObject *)Tkapp_Type;
assert(type != NULL);
assert(type->tp_alloc != NULL);
v = (TkappObject *)type->tp_alloc(type, 0);
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I would prefer to move the variable definition aside to their first assignment:

Suggested change
type = (PyTypeObject *)Tkapp_Type;
assert(type != NULL);
assert(type->tp_alloc != NULL);
v = (TkappObject *)type->tp_alloc(type, 0);
PyTypeObject *type = (PyTypeObject *)Tkapp_Type;
assert(type != NULL);
assert(type->tp_alloc != NULL);
TkappObject *v = (TkappObject *)type->tp_alloc(type, 0);

Same below.

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I followed the existing style. Do you want me to move the char *arg as well?

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Do you want me to move the char *arg as well?

As you want. You can leave argv0 as it is to keep the diff small.

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@picnixz picnixz Sep 10, 2025 •
edited
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I think I would be more comfortable not changing the style of this function. It's a long function, and if we were to use gotos instead for some refactoring, we could benefit for having everything declared at the top. Do you mind I leave it as is?

if (v == NULL)
return NULL;

Expand Down Expand Up @@ -2742,9 +2746,13 @@ _tkinter_tktimertoken_deletetimerhandler_impl(TkttObject *self)
static TkttObject *
Tktt_New(PyObject *func)
{
PyTypeObject *type;
TkttObject *v;

v = PyObject_New(TkttObject, (PyTypeObject *) Tktt_Type);
type = (PyTypeObject *)Tktt_Type;
assert(type != NULL);
assert(type->tp_alloc != NULL);
v = (TkttObject *)type->tp_alloc(type, 0);
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All these types cannot be subclassed. So we can simply replace PyObject_New/PyObject_Free with PyObject_GC_New/PyObject_GC_Del. I think that this would look clearer than with tp_alloc/tp_free.

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@picnixz picnixz Sep 6, 2025 •
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Yes, but now the docs explicitly say "don't call those functions directly, use tp_alloc/tp_free". I agree that when possible, we could directly call them, but @ZeroIntensity suggested to follow the docs here.

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@ZeroIntensity ZeroIntensity Sep 6, 2025 •
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I like using tp_alloc/tp_free more because it's less refactoring if we need to change the type flags. People follow CPython's source code for inspiration in their extensions, so we should follow what's documented. If we want to change the preference, let's update the docs.

Alternatively, we could have a function like this for limited API users:

PyObject *
PyType_InvokeAlloc(PyTypeObject *tp)
{
    assert(tp != NULL);
    assert(type->tp_alloc != NULL);
    return type->tp_alloc(type, 0);
}

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@picnixz picnixz Sep 6, 2025 •
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At this point, I would prefer having a macro to avoid the extra cast everytime... Something that unifies PyObject_[GC_]New(typename, type).

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Suggested change
type = (PyTypeObject *)Tktt_Type;
assert(type != NULL);
assert(type->tp_alloc != NULL);
v = (TkttObject *)type->tp_alloc(type, 0);
v = (TkttObject *)((PyTypeObject *)Tktt_Type)->tp_alloc(type, 0);

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@picnixz picnixz Sep 11, 2025 •
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Unfortunately, we would need

 (TkttObject *)((PyTypeObject *)Tktt_Type)->tp_alloc((PyTypeObject *)Tktt_Type, 0);

which is a bit unreadable IMO. So I'll keep the temporary type variable. I would prefer having a macro for calling tp_alloc because it becomes quite annoying if we need to cast to PyTypeObject* everytime twice.

#define _PyObject_New(T, type)	\
	((T *)((PyTypeObject *)type)->tp_alloc((PyTypeObject *)type, 0))

if (v == NULL)
return NULL;

Expand All @@ -2755,19 +2763,33 @@ Tktt_New(PyObject *func)
return (TkttObject*)Py_NewRef(v);
}

static void
Tktt_Dealloc(PyObject *self)
static int
Tktt_Clear(PyObject *op)
{
TkttObject *v = TkttObject_CAST(self);
PyObject *func = v->func;
PyObject *tp = (PyObject *) Py_TYPE(self);

Py_XDECREF(func);
TkttObject *self = TkttObject_CAST(op);
Py_CLEAR(self->func);
return 0;
}

PyObject_Free(self);
static void
Tktt_Dealloc(PyObject *op)
{
PyTypeObject *tp = Py_TYPE(op);
PyObject_GC_UnTrack(op);
(void)Tktt_Clear(op);
tp->tp_free(op);
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Suggested change
tp->tp_free(op);
Py_TYPE(op)->tp_free(op);

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Unfortunately, this temporary variable is needed as we need Py_DECREF(Py_TYPE(op)) otherwise. The rest of the code base also does this.

Py_DECREF(tp);
}

static int
Tktt_Traverse(PyObject *op, visitproc visit, void *arg)
{
TkttObject *self = TkttObject_CAST(op);
Py_VISIT(Py_TYPE(op));
Py_VISIT(self->func);
return 0;
}

static PyObject *
Tktt_Repr(PyObject *self)
{
Expand Down Expand Up @@ -3058,21 +3080,38 @@ _tkinter_tkapp_willdispatch_impl(TkappObject *self)

/**** Tkapp Type Methods ****/

static int
Tkapp_Clear(PyObject *op)
{
TkappObject *self = TkappObject_CAST(op);
Py_CLEAR(self->trace);
return 0;
}

static void
Tkapp_Dealloc(PyObject *op)
{
PyTypeObject *tp = Py_TYPE(op);
PyObject_GC_UnTrack(op);
TkappObject *self = TkappObject_CAST(op);
PyTypeObject *tp = Py_TYPE(self);
/*CHECK_TCL_APPARTMENT;*/
ENTER_TCL
Tcl_DeleteInterp(Tkapp_Interp(self));
LEAVE_TCL
Py_XDECREF(self->trace);
PyObject_Free(self);
(void)Tkapp_Clear(op);
tp->tp_free(self);
Py_DECREF(tp);
DisableEventHook();
}

static int
Tkapp_Traverse(PyObject *op, visitproc visit, void *arg)
{
TkappObject *self = TkappObject_CAST(op);
Py_VISIT(Py_TYPE(op));
Py_VISIT(self->trace);
return 0;
}


/**** Tkinter Module ****/
Expand Down Expand Up @@ -3260,18 +3299,23 @@ static PyMethodDef Tktt_methods[] =
};

static PyType_Slot Tktt_Type_slots[] = {
{Py_tp_clear, Tktt_Clear},
{Py_tp_dealloc, Tktt_Dealloc},
{Py_tp_traverse, Tktt_Traverse},
{Py_tp_repr, Tktt_Repr},
{Py_tp_methods, Tktt_methods},
{0, 0}
};

static PyType_Spec Tktt_Type_spec = {
"_tkinter.tktimertoken",
sizeof(TkttObject),
0,
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
Tktt_Type_slots,
.name = "_tkinter.tktimertoken",
.basicsize = sizeof(TkttObject),
.flags = (
Py_TPFLAGS_DEFAULT
| Py_TPFLAGS_DISALLOW_INSTANTIATION
| Py_TPFLAGS_HAVE_GC
),
.slots = Tktt_Type_slots,
};


Expand Down Expand Up @@ -3316,18 +3360,23 @@ static PyMethodDef Tkapp_methods[] =
};

static PyType_Slot Tkapp_Type_slots[] = {
{Py_tp_clear, Tkapp_Clear},
{Py_tp_dealloc, Tkapp_Dealloc},
{Py_tp_traverse, Tkapp_Traverse},
{Py_tp_methods, Tkapp_methods},
{0, 0}
};


static PyType_Spec Tkapp_Type_spec = {
"_tkinter.tkapp",
sizeof(TkappObject),
0,
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
Tkapp_Type_slots,
.name = "_tkinter.tkapp",
.basicsize = sizeof(TkappObject),
.flags = (
Py_TPFLAGS_DEFAULT
| Py_TPFLAGS_DISALLOW_INSTANTIATION
| Py_TPFLAGS_HAVE_GC
),
.slots = Tkapp_Type_slots,
};

static PyMethodDef moduleMethods[] =
Expand Down
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