pythongh-117300: Use stop the world to make sys._current_frames and

colesbury · colesbury · commit 214c3a15c692 · 2024-03-27T20:51:25.000Z
`sys._current_exceptions` thread-safe.

This adds a stop the world pause to make the two functions thread-safe
when the GIL is disabled in the free-threaded build.
diff --git a/Python/pystate.c b/Python/pystate.c
@@ -2406,6 +2406,7 @@ _PyThread_CurrentFrames(void)
      * Because these lists can mutate even when the GIL is held, we
      * need to grab head_mutex for the duration.
      */
+    _PyEval_StopTheWorldAll(runtime);
     HEAD_LOCK(runtime);
     PyInterpreterState *i;
     for (i = runtime->interpreters.head; i != NULL; i = i->next) {
@@ -2439,6 +2440,7 @@ _PyThread_CurrentFrames(void)
 
 done:
     HEAD_UNLOCK(runtime);
+    _PyEval_StartTheWorldAll(runtime);
     return result;
 }
 
@@ -2470,6 +2472,7 @@ _PyThread_CurrentExceptions(void)
      * Because these lists can mutate even when the GIL is held, we
      * need to grab head_mutex for the duration.
      */
+    _PyEval_StopTheWorldAll(runtime);
     HEAD_LOCK(runtime);
     PyInterpreterState *i;
     for (i = runtime->interpreters.head; i != NULL; i = i->next) {
@@ -2502,6 +2505,7 @@ _PyThread_CurrentExceptions(void)
 
 done:
     HEAD_UNLOCK(runtime);
+    _PyEval_StartTheWorldAll(runtime);
     return result;
 }
 
