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[3.13] gh-116946: fully implement GC protocol for _curses_panel.panel (GH-138333) #138428

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Merged
merged 1 commit into from
Sep 6, 2025
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[3.13] gh-116946: fully implement GC protocol for _curses_panel.panel (GH-138333) #138428

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89 changes: 76 additions & 13 deletions Modules/_curses_panel.c
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,8 @@ typedef struct {
PyTypeObject *PyCursesPanel_Type;
} _curses_panel_state;

typedef struct PyCursesPanelObject PyCursesPanelObject;

static inline _curses_panel_state *
get_curses_panel_state(PyObject *module)
{
Expand All @@ -40,6 +42,25 @@ get_curses_panel_state(PyObject *module)
return (_curses_panel_state *)state;
}

static inline _curses_panel_state *
get_curses_panel_state_by_panel(PyCursesPanelObject *panel)
{
/*
* Note: 'state' may be NULL if Py_TYPE(panel) is not a heap
* type associated with this module, but the compiler would
* have likely already complained with an "invalid pointer
* type" at compile-time.
*
* To make it more robust, all functions recovering a module's
* state from an object should expect to return NULL with an
* exception set (in contrast to functions recovering a module's
* state from a module itself).
*/
void *state = PyType_GetModuleState(Py_TYPE(panel));
assert(state != NULL);
return (_curses_panel_state *)state;
}

static int
_curses_panel_clear(PyObject *mod)
{
Expand Down Expand Up @@ -95,12 +116,14 @@ PyCursesCheckERR(_curses_panel_state *state, int code, const char *fname)

/* Definition of the panel object and panel type */

typedef struct {
typedef struct PyCursesPanelObject {
PyObject_HEAD
PANEL *pan;
PyCursesWindowObject *wo; /* for reference counts */
} PyCursesPanelObject;

#define _PyCursesPanelObject_CAST(op) ((PyCursesPanelObject *)(op))

/* Some helper functions. The problem is that there's always a window
associated with a panel. To ensure that Python's GC doesn't pull
this window from under our feet we need to keep track of references
Expand Down Expand Up @@ -260,8 +283,11 @@ static PyObject *
PyCursesPanel_New(_curses_panel_state *state, PANEL *pan,
PyCursesWindowObject *wo)
{
PyCursesPanelObject *po = PyObject_New(PyCursesPanelObject,
state->PyCursesPanel_Type);
assert(state != NULL);
PyTypeObject *type = state->PyCursesPanel_Type;
assert(type != NULL);
assert(type->tp_alloc != NULL);
PyCursesPanelObject *po = (PyCursesPanelObject *)type->tp_alloc(type, 0);
if (po == NULL) {
return NULL;
}
Expand All @@ -276,26 +302,57 @@ PyCursesPanel_New(_curses_panel_state *state, PANEL *pan,
return (PyObject *)po;
}

static int
PyCursesPanel_Clear(PyObject *op)
{
PyCursesPanelObject *self = _PyCursesPanelObject_CAST(op);
PyObject *extra = (PyObject *)panel_userptr(self->pan);
if (extra != NULL) {
Py_DECREF(extra);
if (set_panel_userptr(self->pan, NULL) == ERR) {
_curses_panel_state *state = get_curses_panel_state_by_panel(self);
PyErr_SetString(state->PyCursesError,
"set_panel_userptr() returned ERR");
return -1;
}
}
// self->wo should not be cleared because an associated WINDOW may exist
return 0;
}

static void
PyCursesPanel_Dealloc(PyCursesPanelObject *po)
PyCursesPanel_Dealloc(PyObject *self)
{
PyObject *tp, *obj;
PyTypeObject *tp = Py_TYPE(self);
PyObject_GC_UnTrack(self);

tp = (PyObject *) Py_TYPE(po);
obj = (PyObject *) panel_userptr(po->pan);
if (obj) {
(void)set_panel_userptr(po->pan, NULL);
Py_DECREF(obj);
PyCursesPanelObject *po = _PyCursesPanelObject_CAST(self);
if (PyCursesPanel_Clear(self) < 0) {
PyErr_FormatUnraisable("Exception ignored in PyCursesPanel_Dealloc()");
}
if (del_panel(po->pan) == ERR && !PyErr_Occurred()) {
_curses_panel_state *state = get_curses_panel_state_by_panel(po);
PyErr_SetString(state->PyCursesError, "del_panel() returned ERR");
PyErr_FormatUnraisable("Exception ignored in PyCursesPanel_Dealloc()");
}
(void)del_panel(po->pan);
if (po->wo != NULL) {
Py_DECREF(po->wo);
remove_lop(po);
}
PyObject_Free(po);
tp->tp_free(po);
Py_DECREF(tp);
}

static int
PyCursesPanel_Traverse(PyObject *op, visitproc visit, void *arg)
{
PyCursesPanelObject *self = _PyCursesPanelObject_CAST(op);
Py_VISIT(Py_TYPE(op));
Py_VISIT(panel_userptr(self->pan));
Py_VISIT(self->wo);
return 0;
}

/* panel_above(NULL) returns the bottom panel in the stack. To get
this behaviour we use curses.panel.bottom_panel(). */
/*[clinic input]
Expand Down Expand Up @@ -517,15 +574,21 @@ static PyMethodDef PyCursesPanel_Methods[] = {
/* -------------------------------------------------------*/

static PyType_Slot PyCursesPanel_Type_slots[] = {
{Py_tp_clear, PyCursesPanel_Clear},
{Py_tp_dealloc, PyCursesPanel_Dealloc},
{Py_tp_traverse, PyCursesPanel_Traverse},
{Py_tp_methods, PyCursesPanel_Methods},
{0, 0},
};

static PyType_Spec PyCursesPanel_Type_spec = {
.name = "_curses_panel.panel",
.basicsize = sizeof(PyCursesPanelObject),
.flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
.flags = (
Py_TPFLAGS_DEFAULT
| Py_TPFLAGS_DISALLOW_INSTANTIATION
| Py_TPFLAGS_HAVE_GC
),
.slots = PyCursesPanel_Type_slots
};

Expand Down
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