gh-123923: Defer refcounting for `f_funcobj` in `_PyInterpreterFrame` (#124026)

Use a `_PyStackRef` and defer the reference to `f_funcobj` when
possible. This avoids some reference count contention in the common case
of executing the same code object from multiple threads concurrently in
the free-threaded build.

1 files changed, 5 insertions, 4 deletions

diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index b567327f970..9f1c031dcb9 100644
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -1634,7 +1634,7 @@ frame_dealloc(PyFrameObject *f)
     /* Kill all local variables including specials, if we own them */
     if (f->f_frame == frame && frame->owner == FRAME_OWNED_BY_FRAME_OBJECT) {
         PyStackRef_CLEAR(frame->f_executable);
-        Py_CLEAR(frame->f_funcobj);
+        PyStackRef_CLEAR(frame->f_funcobj);
         Py_CLEAR(frame->f_locals);
         _PyStackRef *locals = _PyFrame_GetLocalsArray(frame);
         _PyStackRef *sp = frame->stackpointer;
@@ -1790,7 +1790,7 @@ static void
 init_frame(_PyInterpreterFrame *frame, PyFunctionObject *func, PyObject *locals)
 {
     PyCodeObject *code = (PyCodeObject *)func->func_code;
-    _PyFrame_Initialize(frame, (PyFunctionObject*)Py_NewRef(func),
+    _PyFrame_Initialize(frame, PyStackRef_FromPyObjectNew(func),
                         Py_XNewRef(locals), code, 0, NULL);
 }
 
@@ -1861,14 +1861,15 @@ frame_init_get_vars(_PyInterpreterFrame *frame)
     PyCodeObject *co = _PyFrame_GetCode(frame);
     int lasti = _PyInterpreterFrame_LASTI(frame);
     if (!(lasti < 0 && _PyCode_CODE(co)->op.code == COPY_FREE_VARS
-          && PyFunction_Check(frame->f_funcobj)))
+          && PyStackRef_FunctionCheck(frame->f_funcobj)))
     {
         /* Free vars are initialized */
         return;
     }
 
     /* Free vars have not been initialized -- Do that */
-    PyObject *closure = ((PyFunctionObject *)frame->f_funcobj)->func_closure;
+    PyFunctionObject *func = _PyFrame_GetFunction(frame);
+    PyObject *closure = func->func_closure;
     int offset = PyUnstable_Code_GetFirstFree(co);
     for (int i = 0; i < co->co_nfreevars; ++i) {
         PyObject *o = PyTuple_GET_ITEM(closure, i);