gh-140232: Do not track frozenset objects with immutables

Lib/test/test_sys.py

@@ -1876,7 +1876,10 @@ class S(set):
         check(S(), set(), '3P')
         class FS(frozenset):
             __slots__ = 'a', 'b', 'c'
-        check(FS(), frozenset(), '3P')
+
+        class mytuple(tuple):
+            pass
+        check(FS([mytuple()]), frozenset([mytuple()]), '3P')
         from collections import OrderedDict
         class OD(OrderedDict):
             __slots__ = 'a', 'b', 'c'

Misc/NEWS.d/next/Core_and_Builtins/2025-10-16-22-36-05.gh-issue-140232.u3srgv.rst

@@ -0,0 +1 @@
+Frozenset objects with immutable elements are no longer tracked by the garbage collector.

Modules/_testcapimodule.c

@@ -2435,6 +2435,66 @@ test_critical_sections(PyObject *module, PyObject *Py_UNUSED(args))
 }
 
 
+
+static PyObject *
+test_pyset_add(PyObject* self, PyObject *Py_UNUSED(args))
+{
+
+    PyObject *set = NULL, *empty_tuple=NULL, *tracked_object;
+
+
+    tracked_object = PyImport_ImportModule("sys");
+    if (tracked_object == NULL) {
+        goto failed;
+    }
+    if (!PyObject_GC_IsTracked(tracked_object)) {
+        PyErr_SetString(PyExc_ValueError, "Test item is not tracked by GC");
+        goto failed;
+    }
+
+
+    int return_value;
+    empty_tuple = PyTuple_New(0);
+    if (empty_tuple == NULL) {
+        goto failed;
+    }
+    set = PyFrozenSet_New(empty_tuple);
+    if (set == NULL) {
+        return NULL;
+    }
+
+    if (PyObject_GC_IsTracked(set)) {
+        PyErr_SetString(PyExc_ValueError, "Empty frozenset object is tracked by GC");
+        goto failed;
+    }
+    return_value = PySet_Add(set, empty_tuple);
+    if (return_value<0) {
+        goto failed;
+    }
+    if (PyObject_GC_IsTracked(set)) {
+        PyErr_SetString(PyExc_ValueError, "Frozenset object with immutable is tracked by GC");
+        goto failed;
+    }
+
+    PySet_Add(set, tracked_object);
+    if (return_value<0) {
+        goto failed;
+    }
+    if (!PyObject_GC_IsTracked(set)) {
+        PyErr_SetString(PyExc_ValueError, "Frozenset object with tracked objects is not tracked by GC");
+        goto failed;
+    }
+
+    Py_RETURN_NONE;
+
+failed:
+    Py_XDECREF(tracked_object);
+    Py_XDECREF(empty_tuple);
+    Py_XDECREF(set);
+    return NULL;
+
+}
+
 // Used by `finalize_thread_hang`.
 #if defined(_POSIX_THREADS) && !defined(__wasi__)
 static void finalize_thread_hang_cleanup_callback(void *Py_UNUSED(arg)) {
@@ -2625,7 +2685,7 @@ static PyMethodDef TestMethods[] = {
     {"return_null_without_error", return_null_without_error, METH_NOARGS},
     {"return_result_with_error", return_result_with_error, METH_NOARGS},
     {"getitem_with_error", getitem_with_error, METH_VARARGS},
-    {"Py_CompileString",     pycompilestring, METH_O},
+    {"Py_CompileString", pycompilestring, METH_O},
     {"raise_SIGINT_then_send_None", raise_SIGINT_then_send_None, METH_VARARGS},
     {"stack_pointer", stack_pointer, METH_NOARGS},
 #ifdef W_STOPCODE
@@ -2646,6 +2706,7 @@ static PyMethodDef TestMethods[] = {
     {"gen_get_code", gen_get_code, METH_O, NULL},
     {"get_feature_macros", get_feature_macros, METH_NOARGS, NULL},
     {"test_code_api", test_code_api, METH_NOARGS, NULL},
+    {"test_pyset_add", test_pyset_add, METH_NOARGS, NULL},
     {"settrace_to_error", settrace_to_error, METH_O, NULL},
     {"settrace_to_record", settrace_to_record, METH_O, NULL},
     {"test_macros", test_macros, METH_NOARGS, NULL},

Objects/setobject.c

@@ -1174,6 +1174,23 @@ make_new_set_basetype(PyTypeObject *type, PyObject *iterable)
     return make_new_set(type, iterable);
 }
 
+void
+_PyFrozenSet_MaybeUntrack(PyObject *op)
+{
+    if ((op == NULL) || !(PyFrozenSet_CheckExact(op))) {
+        return;
+    }
+    // if all elements of a frozenset are not tracked, we untrack the object
+    Py_ssize_t pos = 0;
+    setentry *entry;
+    while (set_next((PySetObject *)op, &pos, &entry)) {
+        if (_PyObject_GC_MAY_BE_TRACKED(entry->key)) {
+            return;
+        }
+    }
+    _PyObject_GC_UNTRACK(op);
+}
+
 static PyObject *
 make_new_frozenset(PyTypeObject *type, PyObject *iterable)
 {
@@ -1185,7 +1202,9 @@ make_new_frozenset(PyTypeObject *type, PyObject *iterable)
         /* frozenset(f) is idempotent */
         return Py_NewRef(iterable);
     }
-    return make_new_set(type, iterable);
+    PyObject *obj = make_new_set(type, iterable);
+    _PyFrozenSet_MaybeUntrack(obj);
+    return obj;
 }
 
 static PyObject *
@@ -2710,7 +2729,9 @@ PySet_New(PyObject *iterable)
 PyObject *
 PyFrozenSet_New(PyObject *iterable)
 {
-    return make_new_set(&PyFrozenSet_Type, iterable);
+    PyObject *result = make_new_set(&PyFrozenSet_Type, iterable);
+    _PyFrozenSet_MaybeUntrack(result);
+    return result;
 }
 
 Py_ssize_t
@@ -2779,6 +2800,9 @@ PySet_Add(PyObject *anyset, PyObject *key)
         return -1;
     }
 
+    if (PyFrozenSet_Check(anyset) && PyObject_GC_IsTracked(key) && !PyObject_GC_IsTracked(anyset) ) {
+        _PyObject_GC_TRACK(anyset);
+    }
     int rv;
     Py_BEGIN_CRITICAL_SECTION(anyset);
     rv = set_add_key((PySetObject *)anyset, key);