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gh-152235: Defer GC tracking of set and frozenset to end of construction #152237

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corona10 merged 2 commits into from
Jun 26, 2026
+9 −3
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gh-152235: Defer GC tracking of set and frozenset to end of construction #152237

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gh-152235: Defer GC tracking of a set / frozenset construction from i…
corona10 Jun 25, 2026
365e341
Address code review
corona10 Jun 26, 2026
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-06-26-05-49-13.gh-issue-152235.YU20T9.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Defer GC tracking of a :class:`set` or :class:`frozenset` to the end of its
construction from iterable. Patch by Donghee Na.
10 changes: 7 additions & 3 deletions Objects/setobject.c
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Expand Up @@ -1351,7 +1351,9 @@ make_new_set(PyTypeObject *type, PyObject *iterable)
assert(PyType_Check(type));
PySetObject *so;

so = (PySetObject *)type->tp_alloc(type, 0);
// Allocate untracked: the fill below runs user code, and a half-built
// set must not be reachable from another thread via gc.get_objects().
so = (PySetObject *)_PyType_AllocNoTrack(type, 0);

@sergey-miryanov sergey-miryanov Jun 25, 2026

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Should we update the type spec and remove PyType_GenericAlloc from tp_alloc?

@corona10 corona10 Jun 26, 2026

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Nice catch :)

if (so == NULL)
return NULL;

Expand All @@ -1370,6 +1372,8 @@ make_new_set(PyTypeObject *type, PyObject *iterable)
}
}

// Track only once fully built.
_PyObject_GC_TRACK(so);
return (PyObject *)so;
}

Expand Down Expand Up @@ -2885,7 +2889,7 @@ PyTypeObject PySet_Type = {
0, /* tp_descr_set */
0, /* tp_dictoffset */
set_init, /* tp_init */
PyType_GenericAlloc, /* tp_alloc */
_PyType_AllocNoTrack, /* tp_alloc */
set_new, /* tp_new */
PyObject_GC_Del, /* tp_free */
.tp_vectorcall = set_vectorcall,
Expand Down Expand Up @@ -2977,7 +2981,7 @@ PyTypeObject PyFrozenSet_Type = {
0, /* tp_descr_set */
0, /* tp_dictoffset */
0, /* tp_init */
PyType_GenericAlloc, /* tp_alloc */
_PyType_AllocNoTrack, /* tp_alloc */
frozenset_new, /* tp_new */
PyObject_GC_Del, /* tp_free */
.tp_vectorcall = frozenset_vectorcall,
Expand Down
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