gh-133931: Introduce _PyObject_XSetRefDelayed to replace Py_XSETREF

Include/internal/pycore_pymem.h

@@ -100,6 +100,18 @@ static inline void _PyObject_XDecRefDelayed(PyObject *obj)
 }
 #endif
 
+#ifdef Py_GIL_DISABLED
+// This is the delayed-free equivalent of Py_XSETREF(), providing the same
+// atomic reference assignment semantics but with deferred cleanup suitable
+// for concurrent access patterns in free-threaded Python.
+PyAPI_FUNC(void) _PyObject_XSetRefDelayed(PyObject **p_obj, PyObject *obj);
+#else
+static inline void _PyObject_XSetRefDelayed(PyObject **p_obj, PyObject *obj)
+{
+    Py_XSETREF(*p_obj, obj);
+}
+#endif
+
 // Periodically process delayed free requests.
 extern void _PyMem_ProcessDelayed(PyThreadState *tstate);
 

Objects/genobject.c

@@ -10,6 +10,7 @@
 #include "pycore_gc.h"            // _PyGC_CLEAR_FINALIZED()
 #include "pycore_genobject.h"     // _PyGen_SetStopIterationValue()
 #include "pycore_interpframe.h"   // _PyFrame_GetCode()
+#include "pycore_pymem.h"         // _PyObject_XSetRefDelayed()
 #include "pycore_modsupport.h"    // _PyArg_CheckPositional()
 #include "pycore_object.h"        // _PyObject_GC_UNTRACK()
 #include "pycore_opcode_utils.h"  // RESUME_AFTER_YIELD_FROM
@@ -718,7 +719,9 @@ gen_set_name(PyObject *self, PyObject *value, void *Py_UNUSED(ignored))
                         "__name__ must be set to a string object");
         return -1;
     }
-    Py_XSETREF(op->gi_name, Py_NewRef(value));
+    Py_BEGIN_CRITICAL_SECTION(self);
+    _PyObject_XSetRefDelayed(&op->gi_name, Py_NewRef(value));
+    Py_END_CRITICAL_SECTION();
     return 0;
 }
 
@@ -740,7 +743,9 @@ gen_set_qualname(PyObject *self, PyObject *value, void *Py_UNUSED(ignored))
                         "__qualname__ must be set to a string object");
         return -1;
     }
-    Py_XSETREF(op->gi_qualname, Py_NewRef(value));
+    Py_BEGIN_CRITICAL_SECTION(self);
+    _PyObject_XSetRefDelayed(&op->gi_qualname, Py_NewRef(value));
+    Py_END_CRITICAL_SECTION();
     return 0;
 }
 

Objects/obmalloc.c

@@ -1231,6 +1231,24 @@ _PyObject_XDecRefDelayed(PyObject *ptr)
 }
 #endif
 
+#ifdef Py_GIL_DISABLED
+void
+_PyObject_XSetRefDelayed(PyObject **ptr, PyObject *value)
+{
+    PyObject *old = *ptr;
+    FT_ATOMIC_STORE_PTR_RELEASE(*ptr, value);
+    if (old == _Py_NULL) {
+        return;
+    }
+    if (!_Py_IsImmortal(old)) {
+         _PyObject_XDecRefDelayed(old);
+    }
+    else {
+         Py_DECREF(old);
+    }
+}
+#endif
+
 static struct _mem_work_chunk *
 work_queue_first(struct llist_node *head)
 {

Objects/typeobject.c

@@ -3967,13 +3967,7 @@ _PyObject_SetDict(PyObject *obj, PyObject *value)
         return -1;
     }
     Py_BEGIN_CRITICAL_SECTION(obj);
-    PyObject *olddict = *dictptr;
-    FT_ATOMIC_STORE_PTR_RELEASE(*dictptr, Py_NewRef(value));
-#ifdef Py_GIL_DISABLED
-    _PyObject_XDecRefDelayed(olddict);
-#else
-    Py_XDECREF(olddict);
-#endif
+    _PyObject_XSetRefDelayed(dictptr, Py_NewRef(value));
     Py_END_CRITICAL_SECTION();
     return 0;
 }