gh-158364: Don't report other interpreters' threads in sys._current_frames (GH-158369)

Author: Himesh-rupchandani

Lib/test/test_sys.py

@@ -563,6 +563,38 @@ def g456():
             leave_g.set()
             t.join()
 
+    @support.cpython_only
+    @requires_subinterpreters
+    @threading_helper.requires_working_threading()
+    def test_current_frames_other_interpreters(self):
+        # gh-158364: sys._current_frames() would access frames of another
+        # interpreter and crash
+        import threading
+
+        entered = threading.Event()
+        left = threading.Event()
+
+        def park():
+            entered.set()
+            left.wait()
+
+        t = threading.Thread(target=park)
+        with threading_helper.start_threads([t], unlock=left.set):
+            entered.wait()
+            interp = interpreters.create()
+            try:
+                interp.exec(f"""if True:
+                    import sys
+                    import threading
+
+                    frames = sys._current_frames()
+                    assert threading.get_ident() in frames, frames
+                    assert frames[threading.get_ident()].f_globals is globals()
+                    assert {t.ident} not in frames, frames
+                    """)
+            finally:
+                interp.close()
+
     @threading_helper.reap_threads
     @threading_helper.requires_working_threading()
     def test_current_exceptions(self):
@@ -629,6 +661,39 @@ def g456():
             leave_g.set()
             t.join()
 
+    @support.cpython_only
+    @requires_subinterpreters
+    @threading_helper.requires_working_threading()
+    def test_current_exceptions_other_interpreters(self):
+        # gh-158364: sys._current_exceptions() would hand out exceptions of
+        # another interpreter and crash
+        import threading
+
+        entered = threading.Event()
+        left = threading.Event()
+
+        def hold():
+            # The thread has to be handling an exception, otherwise
+            # sys._current_exceptions() has nothing to report for it.
+            try:
+                raise ValueError
+            except ValueError:
+                entered.set()
+                left.wait()
+
+        t = threading.Thread(target=hold)
+        with threading_helper.start_threads([t], unlock=left.set):
+            entered.wait()
+            interp = interpreters.create()
+            try:
+                interp.exec(f"""if True:
+                    import sys
+
+                    assert {t.ident} not in sys._current_exceptions()
+                    """)
+            finally:
+                interp.close()
+
     def test_attributes(self):
         self.assertIsInstance(sys.api_version, int)
         self.assertIsInstance(sys.argv, list)

Misc/NEWS.d/next/Core_and_Builtins/2026-09-28-18-58-27.gh-issue-158364.jBqmTs.rst

@@ -0,0 +1,3 @@
+Fix crash when :func:`sys._current_frames` or
+:func:`sys._current_exceptions` is called while another interpreter is
+running.

Python/pystate.c

@@ -2801,36 +2801,33 @@ _PyThread_CurrentFrames(void)
         return NULL;
     }
 
-    /* for i in all interpreters:
-     *     for t in all of i's thread states:
-     *          if t's frame isn't NULL, map t's id to its frame
+    /* for t in all of the current interpreter's thread states:
+     *     if t's frame isn't NULL, map t's id to its frame
      * Because these lists can mutate even when the GIL is held, we
      * need to grab head_mutex for the duration.
      */
-    _PyEval_StopTheWorldAll(runtime);
+    PyInterpreterState *interp = tstate->interp;
+    _PyEval_StopTheWorld(interp);
     HEAD_LOCK(runtime);
-    PyInterpreterState *i;
-    for (i = runtime->interpreters.head; i != NULL; i = i->next) {
-        _Py_FOR_EACH_TSTATE_UNLOCKED(i, t) {
-            _PyInterpreterFrame *frame = t->current_frame;
-            frame = _PyFrame_GetFirstComplete(frame);
-            if (frame == NULL) {
-                continue;
-            }
-            PyObject *id = PyLong_FromUnsignedLong(t->thread_id);
-            if (id == NULL) {
-                goto fail;
-            }
-            PyObject *frameobj = (PyObject *)_PyFrame_GetFrameObject(frame);
-            if (frameobj == NULL) {
-                Py_DECREF(id);
-                goto fail;
-            }
-            int stat = PyDict_SetItem(result, id, frameobj);
+    _Py_FOR_EACH_TSTATE_UNLOCKED(interp, t) {
+        _PyInterpreterFrame *frame = t->current_frame;
+        frame = _PyFrame_GetFirstComplete(frame);
+        if (frame == NULL) {
+            continue;
+        }
+        PyObject *id = PyLong_FromUnsignedLong(t->thread_id);
+        if (id == NULL) {
+            goto fail;
+        }
+        PyObject *frameobj = (PyObject *)_PyFrame_GetFrameObject(frame);
+        if (frameobj == NULL) {
             Py_DECREF(id);
-            if (stat < 0) {
-                goto fail;
-            }
+            goto fail;
+        }
+        int stat = PyDict_SetItem(result, id, frameobj);
+        Py_DECREF(id);
+        if (stat < 0) {
+            goto fail;
         }
     }
     goto done;
@@ -2840,7 +2837,7 @@ _PyThread_CurrentFrames(void)
 
 done:
     HEAD_UNLOCK(runtime);
-    _PyEval_StartTheWorldAll(runtime);
+    _PyEval_StartTheWorld(interp);
     return result;
 }
 
@@ -2866,35 +2863,32 @@ _PyThread_CurrentExceptions(void)
         return NULL;
     }
 
-    /* for i in all interpreters:
-     *     for t in all of i's thread states:
-     *          if t's frame isn't NULL, map t's id to its frame
+    /* for t in all of the current interpreter's thread states:
+     *     if t's frame isn't NULL, map t's id to its exception
      * Because these lists can mutate even when the GIL is held, we
      * need to grab head_mutex for the duration.
      */
-    _PyEval_StopTheWorldAll(runtime);
+    PyInterpreterState *interp = tstate->interp;
+    _PyEval_StopTheWorld(interp);
     HEAD_LOCK(runtime);
-    PyInterpreterState *i;
-    for (i = runtime->interpreters.head; i != NULL; i = i->next) {
-        _Py_FOR_EACH_TSTATE_UNLOCKED(i, t) {
-            _PyErr_StackItem *err_info = _PyErr_GetTopmostException(t);
-            if (err_info == NULL) {
-                continue;
-            }
-            PyObject *id = PyLong_FromUnsignedLong(t->thread_id);
-            if (id == NULL) {
-                goto fail;
-            }
-            PyObject *exc = err_info->exc_value;
-            assert(exc == NULL ||
-                   exc == Py_None ||
-                   PyExceptionInstance_Check(exc));
-
-            int stat = PyDict_SetItem(result, id, exc == NULL ? Py_None : exc);
-            Py_DECREF(id);
-            if (stat < 0) {
-                goto fail;
-            }
+    _Py_FOR_EACH_TSTATE_UNLOCKED(interp, t) {
+        _PyErr_StackItem *err_info = _PyErr_GetTopmostException(t);
+        if (err_info == NULL) {
+            continue;
+        }
+        PyObject *id = PyLong_FromUnsignedLong(t->thread_id);
+        if (id == NULL) {
+            goto fail;
+        }
+        PyObject *exc = err_info->exc_value;
+        assert(exc == NULL ||
+               exc == Py_None ||
+               PyExceptionInstance_Check(exc));
+
+        int stat = PyDict_SetItem(result, id, exc == NULL ? Py_None : exc);
+        Py_DECREF(id);
+        if (stat < 0) {
+            goto fail;
         }
     }
     goto done;
@@ -2904,7 +2898,7 @@ _PyThread_CurrentExceptions(void)
 
 done:
     HEAD_UNLOCK(runtime);
-    _PyEval_StartTheWorldAll(runtime);
+    _PyEval_StartTheWorld(interp);
     return result;
 }