[3.13] gh-152235: Defer GC tracking in more set operations (gh-152273) (gh-152280)

gh-152235: Defer GC tracking in more set operations (gh-152273)
(cherry picked from commit a87d24a)
Co-authored-by: Donghee Na <donghee.na@python.org>

Author: miss-islington

Misc/NEWS.d/next/Core_and_Builtins/2026-06-26-22-03-16.gh-issue-152235.ZKWiWk.rst

@@ -0,0 +1,2 @@
+Defer GC tracking of :meth:`set.intersection`, :meth:`set.difference` and
+:meth:`set.symmetric_difference`. Patch by Donghee Na.

Objects/setobject.c

@@ -1080,14 +1080,14 @@ set_update_impl(PySetObject *so, PyObject *args)
  can be retrieved or updated in a single cache line.
 */
 
+// Build a set/frozenset left GC-untracked; the caller must _PyObject_GC_TRACK()
+// it once fully built, so a half-built set is never exposed during filling.
 staticPyObject*
-make_new_set(PyTypeObject*type, PyObject*iterable)
+make_new_set_untracked(PyTypeObject*type, PyObject*iterable)
 {
 assert(PyType_Check(type));
 PySetObject*so;
 
-// 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);
 if (so==NULL)
 returnNULL;
@@ -1107,21 +1107,39 @@ make_new_set(PyTypeObject *type, PyObject *iterable)
  }
  }
 
-// Track only once fully built.
-_PyObject_GC_TRACK(so);
 return (PyObject*)so;
 }
 
 staticPyObject*
-make_new_set_basetype(PyTypeObject*type, PyObject*iterable)
+make_new_set(PyTypeObject*type, PyObject*iterable)
+{
+PyObject*so=make_new_set_untracked(type, iterable);
+if (so!=NULL) {
+_PyObject_GC_TRACK(so);
+ }
+returnso;
+}
+
+staticPyObject*
+make_new_set_basetype_untracked(PyTypeObject*type, PyObject*iterable)
 {
 if (type!=&PySet_Type&&type!=&PyFrozenSet_Type) {
 if (PyType_IsSubtype(type, &PySet_Type))
 type=&PySet_Type;
 else
 type=&PyFrozenSet_Type;
  }
-returnmake_new_set(type, iterable);
+returnmake_new_set_untracked(type, iterable);
+}
+
+staticPyObject*
+make_new_set_basetype(PyTypeObject*type, PyObject*iterable)
+{
+PyObject*so=make_new_set_basetype_untracked(type, iterable);
+if (so!=NULL) {
+_PyObject_GC_TRACK(so);
+ }
+returnso;
 }
 
 staticPyObject*
@@ -1364,7 +1382,7 @@ set_intersection(PySetObject *so, PyObject *other)
 if ((PyObject*)so==other)
 returnset_copy_impl(so);
 
-result= (PySetObject*)make_new_set_basetype(Py_TYPE(so), NULL);
+result= (PySetObject*)make_new_set_basetype_untracked(Py_TYPE(so), NULL);
 if (result==NULL)
 returnNULL;
 
@@ -1397,6 +1415,7 @@ set_intersection(PySetObject *so, PyObject *other)
  }
 Py_DECREF(key);
  }
+_PyObject_GC_TRACK(result);
 return (PyObject*)result;
  }
 
@@ -1428,6 +1447,7 @@ set_intersection(PySetObject *so, PyObject *other)
 Py_DECREF(result);
 returnNULL;
  }
+_PyObject_GC_TRACK(result);
 return (PyObject*)result;
 error:
 Py_DECREF(it);
@@ -1737,7 +1757,7 @@ set_difference(PySetObject *so, PyObject *other)
 returnset_copy_and_difference(so, other);
  }
 
-result=make_new_set_basetype(Py_TYPE(so), NULL);
+result=make_new_set_basetype_untracked(Py_TYPE(so), NULL);
 if (result==NULL)
 returnNULL;
 
@@ -1761,6 +1781,7 @@ set_difference(PySetObject *so, PyObject *other)
  }
 Py_DECREF(key);
  }
+_PyObject_GC_TRACK(result);
 returnresult;
  }
 
@@ -1784,6 +1805,7 @@ set_difference(PySetObject *so, PyObject *other)
  }
 Py_DECREF(key);
  }
+_PyObject_GC_TRACK(result);
 returnresult;
 }
 
@@ -1970,7 +1992,8 @@ static PyObject *
 set_symmetric_difference_impl(PySetObject*so, PyObject*other)
 /*[clinic end generated code: output=270ee0b5d42b0797 input=624f6e7bbdf70db1]*/
 {
-PySetObject*result= (PySetObject*)make_new_set_basetype(Py_TYPE(so), NULL);
+PySetObject*result=
+ (PySetObject*)make_new_set_basetype_untracked(Py_TYPE(so), NULL);
 if (result==NULL) {
 returnNULL;
  }
@@ -1982,6 +2005,7 @@ set_symmetric_difference_impl(PySetObject *so, PyObject *other)
 Py_DECREF(result);
 returnNULL;
  }
+_PyObject_GC_TRACK(result);
 return (PyObject*)result;
 }