bpo-40429: PyThreadState_GetFrame() returns a strong ref (pythonGH-19781)

The PyThreadState_GetFrame() function now returns a strong reference
to the frame.

Author: vstinner

Doc/c-api/init.rst

@@ -1074,10 +1074,10 @@ All of the following functions must be called after :c:func:`Py_Initialize`.
 
 .. c:function:: PyFrameObject* PyThreadState_GetFrame(PyThreadState *tstate)
 
-   Get a borrowed reference to the current frame of the Python thread state
-   *tstate*.
+   Get the current frame of the Python thread state *tstate*.
 
-   Return ``NULL`` if no frame is currently executing.
+   Return a strong reference. Return ``NULL`` if no frame is currently
+   executing.
 
    See also :c:func:`PyEval_GetFrame`.
 

Misc/NEWS.d/next/C API/2020-04-29-01-39-41.bpo-40429.VQfvta.rst

@@ -0,0 +1,2 @@
+The :c:func:`PyThreadState_GetFrame` function now returns a strong reference
+to the frame.

Modules/_tracemalloc.c

@@ -425,18 +425,16 @@ traceback_hash(traceback_t *traceback)
 static void
 traceback_get_frames(traceback_t *traceback)
 {
-    PyThreadState *tstate;
-    PyFrameObject *pyframe;
-
-    tstate = PyGILState_GetThisThreadState();
+    PyThreadState *tstate = PyGILState_GetThisThreadState();
     if (tstate == NULL) {
 #ifdef TRACE_DEBUG
         tracemalloc_error("failed to get the current thread state");
 #endif
         return;
     }
 
-    pyframe = PyThreadState_GetFrame(tstate);
+    PyFrameObject *pyframe = PyThreadState_GetFrame(tstate);
+    Py_XDECREF(pyframe); // use a borrowed reference
     for (; pyframe != NULL; pyframe = pyframe->f_back) {
         if (traceback->nframe < _Py_tracemalloc_config.max_nframe) {
             tracemalloc_get_frame(pyframe, &traceback->frames[traceback->nframe]);

Modules/_xxsubinterpretersmodule.c

@@ -1840,14 +1840,17 @@ _is_running(PyInterpreterState *interp)
                         "interpreter has more than one thread");
         return -1;
     }
+
+    assert(!PyErr_Occurred());
     PyFrameObject *frame = PyThreadState_GetFrame(tstate);
     if (frame == NULL) {
-        if (PyErr_Occurred() != NULL) {
-            return -1;
-        }
         return 0;
     }
-    return (int)(frame->f_executing);
+
+    int executing = (int)(frame->f_executing);
+    Py_DECREF(frame);
+
+    return executing;
 }
 
 static int

Objects/typeobject.c

@@ -8108,15 +8108,16 @@ super_init(PyObject *self, PyObject *args, PyObject *kwds)
         /* Call super(), without args -- fill in from __class__
            and first local variable on the stack. */
         PyThreadState *tstate = _PyThreadState_GET();
-        PyFrameObject *f = PyThreadState_GetFrame(tstate);
-        if (f == NULL) {
+        PyFrameObject *frame = PyThreadState_GetFrame(tstate);
+        if (frame == NULL) {
             PyErr_SetString(PyExc_RuntimeError,
                             "super(): no current frame");
             return -1;
         }
 
-        PyCodeObject *code = PyFrame_GetCode(f);
-        int res = super_init_without_args(f, code, &type, &obj);
+        PyCodeObject *code = PyFrame_GetCode(frame);
+        int res = super_init_without_args(frame, code, &type, &obj);
+        Py_DECREF(frame);
         Py_DECREF(code);
 
         if (res < 0) {

Python/errors.c

@@ -1372,7 +1372,7 @@ _PyErr_WriteUnraisableMsg(const char *err_msg_str, PyObject *obj)
     }
 
     if (exc_tb == NULL) {
-        struct _frame *frame = tstate->frame;
+        PyFrameObject *frame = tstate->frame;
         if (frame != NULL) {
             exc_tb = _PyTraceBack_FromFrame(NULL, frame);
             if (exc_tb == NULL) {

Python/pystate.c

@@ -1042,11 +1042,13 @@ PyThreadState_GetInterpreter(PyThreadState *tstate)
 }
 
 
-struct _frame*
+PyFrameObject*
 PyThreadState_GetFrame(PyThreadState *tstate)
 {
     assert(tstate != NULL);
-    return tstate->frame;
+    PyFrameObject *frame = tstate->frame;
+    Py_XINCREF(frame);
+    return frame;
 }
 
 
@@ -1165,7 +1167,7 @@ _PyThread_CurrentFrames(void)
     for (i = runtime->interpreters.head; i != NULL; i = i->next) {
         PyThreadState *t;
         for (t = i->tstate_head; t != NULL; t = t->next) {
-            struct _frame *frame = t->frame;
+            PyFrameObject *frame = t->frame;
             if (frame == NULL) {
                 continue;
             }