gh-125512: Revert "gh-124872: Replace enter/exit events with "switched" (#124776)" (#125513)

1 files changed, 10 insertions, 21 deletions

diff --git a/Python/context.c b/Python/context.c
index 95aa822..8bc487a 100644
--- a/Python/context.c
+++ b/Python/context.c
@@ -102,8 +102,10 @@ PyContext_CopyCurrent(void)
 static const char *
 context_event_name(PyContextEvent event) {
     switch (event) {
-        case Py_CONTEXT_SWITCHED:
-            return "Py_CONTEXT_SWITCHED";
+        case Py_CONTEXT_EVENT_ENTER:
+            return "Py_CONTEXT_EVENT_ENTER";
+        case Py_CONTEXT_EVENT_EXIT:
+            return "Py_CONTEXT_EVENT_EXIT";
         default:
             return "?";
     }
@@ -113,13 +115,6 @@ context_event_name(PyContextEvent event) {
 static void
 notify_context_watchers(PyThreadState *ts, PyContextEvent event, PyObject *ctx)
 {
-    if (ctx == NULL) {
-        // This will happen after exiting the last context in the stack, which
-        // can occur if context_get was never called before entering a context
-        // (e.g., called `contextvars.Context().run()` on a fresh thread, as
-        // PyContext_Enter doesn't call context_get).
-        ctx = Py_None;
-    }
     assert(Py_REFCNT(ctx) > 0);
     PyInterpreterState *interp = ts->interp;
     assert(interp->_initialized);
@@ -180,16 +175,6 @@ PyContext_ClearWatcher(int watcher_id)
 }
 
 
-static inline void
-context_switched(PyThreadState *ts)
-{
-    ts->context_ver++;
-    // ts->context is used instead of context_get() because context_get() might
-    // throw if ts->context is NULL.
-    notify_context_watchers(ts, Py_CONTEXT_SWITCHED, ts->context);
-}
-
-
 static int
 _PyContext_Enter(PyThreadState *ts, PyObject *octx)
 {
@@ -206,7 +191,9 @@ _PyContext_Enter(PyThreadState *ts, PyObject *octx)
     ctx->ctx_entered = 1;
 
     ts->context = Py_NewRef(ctx);
-    context_switched(ts);
+    ts->context_ver++;
+
+    notify_context_watchers(ts, Py_CONTEXT_EVENT_ENTER, octx);
     return 0;
 }
 
@@ -240,11 +227,13 @@ _PyContext_Exit(PyThreadState *ts, PyObject *octx)
         return -1;
     }
 
+    notify_context_watchers(ts, Py_CONTEXT_EVENT_EXIT, octx);
     Py_SETREF(ts->context, (PyObject *)ctx->ctx_prev);
+    ts->context_ver++;
 
     ctx->ctx_prev = NULL;
     ctx->ctx_entered = 0;
-    context_switched(ts);
+
     return 0;
 }