gh-152235: Defer GC tracking during the lock-free fill in set.init by corona10 · Pull Request #153079 · python/cpython · GitHub

Issue: Need to defer GC tracking of frozenset/set construction #152235

…_init__

Final PR of the set: list already has TSan-safe initialization, and this brings set.init up to the same level of protection.

cpython/Objects/listobject.c

Lines 3523 to 3544 in fe9c721

    
           list___init___impl(PyListObject *self, PyObject *iterable) 
        
           /*[clinic end generated code: output=0f3c21379d01de48 input=b3f3fe7206af8f6b]*/ 
        
           { 
        
               /* Verify list invariants established by PyType_GenericAlloc() */ 
        
               assert(0 <= Py_SIZE(self)); 
        
               assert(Py_SIZE(self) <= self->allocated || self->allocated == -1); 
        
               assert(self->ob_item != NULL || 
        
                      self->allocated == 0 || self->allocated == -1); 
        
               /* Empty previous contents */ 
        
               if (self->ob_item != NULL) { 
        
                   Py_BEGIN_CRITICAL_SECTION(self); 
        
                   list_clear(self); 
        
                   Py_END_CRITICAL_SECTION(); 
        
               } 
        
               if (iterable != NULL) { 
        
                   if (_list_extend(self, iterable) < 0) { 
        
                       return -1; 
        
                   } 
        
               } 
        
               return 0; 
        
           }

cpython/Objects/listobject.c

Lines 1457 to 1511 in fe9c721

    
           _list_extend(PyListObject *self, PyObject *iterable) 
        
           { 
        
               // Special case: 
        
               // lists and tuples which can use PySequence_Fast ops 
        
               int res = -1; 
        
               if ((PyObject *)self == iterable) { 
        
                   Py_BEGIN_CRITICAL_SECTION(self); 
        
                   res = list_inplace_repeat_lock_held(self, 2); 
        
                   Py_END_CRITICAL_SECTION(); 
        
               } 
        
               else if (PyList_CheckExact(iterable)) { 
        
                   Py_BEGIN_CRITICAL_SECTION2(self, iterable); 
        
                   res = list_extend_lock_held(self, iterable); 
        
                   Py_END_CRITICAL_SECTION2(); 
        
               } 
        
               else if (PyTuple_CheckExact(iterable)) { 
        
                   Py_BEGIN_CRITICAL_SECTION(self); 
        
                   res = list_extend_lock_held(self, iterable); 
        
                   Py_END_CRITICAL_SECTION(); 
        
               } 
        
               else if (PyAnySet_CheckExact(iterable)) { 
        
                   Py_BEGIN_CRITICAL_SECTION2(self, iterable); 
        
                   res = list_extend_set(self, (PySetObject *)iterable); 
        
                   Py_END_CRITICAL_SECTION2(); 
        
               } 
        
               else if (PyDict_CheckExact(iterable)) { 
        
                   Py_BEGIN_CRITICAL_SECTION2(self, iterable); 
        
                   res = list_extend_dict(self, (PyDictObject *)iterable, 0 /*keys*/); 
        
                   Py_END_CRITICAL_SECTION2(); 
        
               } 
        
               else if (Py_IS_TYPE(iterable, &PyDictKeys_Type)) { 
        
                   PyDictObject *dict = ((_PyDictViewObject *)iterable)->dv_dict; 
        
                   Py_BEGIN_CRITICAL_SECTION2(self, dict); 
        
                   res = list_extend_dict(self, dict, 0 /*keys*/); 
        
                   Py_END_CRITICAL_SECTION2(); 
        
               } 
        
               else if (Py_IS_TYPE(iterable, &PyDictValues_Type)) { 
        
                   PyDictObject *dict = ((_PyDictViewObject *)iterable)->dv_dict; 
        
                   Py_BEGIN_CRITICAL_SECTION2(self, dict); 
        
                   res = list_extend_dict(self, dict, 1 /*values*/); 
        
                   Py_END_CRITICAL_SECTION2(); 
        
               } 
        
               else if (Py_IS_TYPE(iterable, &PyDictItems_Type)) { 
        
                   PyDictObject *dict = ((_PyDictViewObject *)iterable)->dv_dict; 
        
                   Py_BEGIN_CRITICAL_SECTION2(self, dict); 
        
                   res = list_extend_dictitems(self, dict); 
        
                   Py_END_CRITICAL_SECTION2(); 
        
               } 
        
               else { 
        
                   Py_BEGIN_CRITICAL_SECTION(self); 
        
                   res = list_extend_iter_lock_held(self, iterable); 
        
                   Py_END_CRITICAL_SECTION(); 
        
               } 
        
               return res; 
        
           }

The issue title is "Need to defer GC tracking of frozenset/set construction", but in fact, the problem only arises for frozenset.

PyFrozenSet_Type defines tp_new (frozenset_new) but has no tp_init function.

PySet_Type defines tp_new (set_new) and tp_init (set_init).

So changing set_init() only impacts the mutable set. I don't see which problem you are trying to solve. It's fine to mutate a set object.

Yeah we don't need to handle

pythongh-152235 : Defer GC tracking during the lock-free fill in set._…

48afcee

…_init__

corona10 requested a review from rhettinger as a code owner July 5, 2026 08:05

bedevere-app Bot mentioned this pull request Jul 5, 2026

Need to defer GC tracking of frozenset/set construction #152235

Closed

bedevere-app Bot added the awaiting core review label Jul 5, 2026

corona10 added topic-free-threading needs backport to 3.13 only security fixes needs backport to 3.14 bugs and security fixes needs backport to 3.15 bugs and security fixes skip news and removed awaiting core review labels Jul 5, 2026

corona10 requested review from methane and vstinner July 5, 2026 08:05

corona10 closed this Jul 14, 2026

gh-152235: Defer GC tracking during the lock-free fill in set.init by corona10 · Pull Request #153079 · python/cpython · GitHub

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gh-152235: Defer GC tracking during the lock-free fill in set.init - #153079

gh-152235: Defer GC tracking during the lock-free fill in set.init#153079
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gh-152235: Defer GC tracking during the lock-free fill in set.__init__ by corona10 · Pull Request #153079 · python/cpython · GitHub

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gh-152235: Defer GC tracking during the lock-free fill in set.__init__ - #153079

gh-152235: Defer GC tracking during the lock-free fill in set.__init__#153079corona10 wants to merge 1 commit intopython:mainpython/cpython:mainfrom corona10:gh-152235-set-initcorona10/cpython:gh-152235-set-initCopy head branch name to clipboard

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gh-152235: Defer GC tracking during the lock-free fill in set.init by corona10 · Pull Request #153079 · python/cpython · GitHub

gh-152235: Defer GC tracking during the lock-free fill in set.init - #153079

gh-152235: Defer GC tracking during the lock-free fill in set.init#153079
corona10 wants to merge 1 commit into
python:mainfrom
corona10:gh-152235-set-init

corona10 commented Jul 5, 2026 •
edited by bedevere-app Bot
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