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gh-138791: fix crash when visiting a non-consumed timer handler #138789

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gh-138791: fix crash when visiting a non-consumed timer handler #138789

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714274c
fix crash when visiting a non-consumed timer handler
picnixz Sep 11, 2025
3873fd5
add regression test
picnixz Sep 11, 2025
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17 changes: 17 additions & 0 deletions Lib/test/test_tkinter/test_misc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -508,6 +508,23 @@ def test_embedded_null(self):
widget.selection_range(0, 'end')
self.assertEqual(widget.selection_get(), '\u20ac\0abc\x00def')

def test_settrace_gc(self):
# Regression test for https://github.com/python/cpython/issues/138791.
root = tkinter.Tk()
trace = lambda *_, **__: None
trace.evil = type(root.tk)
root.tk.settrace(trace)
root.destroy()

def test_createtimerhandler_gc(self):
# Regression test for https://github.com/python/cpython/issues/138791.
root = tkinter.Tk()
func = lambda *_, **__: None
func.evil = type(root.tk.createtimerhandler(0, print))
# Large timeout (in ms) so that the object is destroyed before.
root.tk.createtimerhandler(1234567, func)
root.destroy()


class WmTest(AbstractTkTest, unittest.TestCase):

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12 changes: 11 additions & 1 deletion Modules/_tkinter.c
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Expand Up @@ -2764,7 +2764,14 @@ static int
Tktt_Clear(PyObject *op)
{
TkttObject *self = TkttObject_CAST(op);
Py_CLEAR(self->func);
if (self->token != NULL) {
Tcl_DeleteTimerHandler(self->token);
self->token = NULL;
}
if (self->func != NULL) {
Py_CLEAR(self->func);
Py_DECREF(op); /* See Tktt_New() */
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Again, I'm probably missing something -- why do we have that extra reference in the first place?

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To prevent the result of createtimerhandler() from being collected before the timer fires.

}
return 0;
}

Expand All @@ -2783,6 +2790,9 @@ Tktt_Traverse(PyObject *op, visitproc visit, void *arg)
{
TkttObject *self = TkttObject_CAST(op);
Py_VISIT(Py_TYPE(op));
if (self->token != NULL) {
Py_VISIT(op); /* See Tktt_New() */
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I might be missing something, but won't this just lead to infinite recursion?

}
Py_VISIT(self->func);
return 0;
}
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