Revert Solution 2 (loop.stop() method) due to persistent test failures

Solution 2 introduced persistent test failures in test_idle_heartbeat that
could not be diagnosed due to incomplete error messages. Since Solution 1
(fix atexit registration) was already approved and addresses the core issue
of Python shutdown crashes, reverting Solution 2 to maintain stability.

This commit reverts:
- f296d57: Implement Solution 2: Add loop.stop() method
- 10dd871: Fix async_watcher reference counting
- c65c5c5: Remove explicit ev_async_stop in Loop_dealloc

Keeping only Solution 1 (a2ed376) which:
- Fixes atexit registration to pass actual _global_loop instead of None
- Was approved with "LGTM" from @fruch
- Addresses the original shutdown crash issue without introducing test failures

The loop.stop() functionality can be reconsidered in the future if needed,
but only after proper testing and diagnosis of the test_idle_heartbeat issues.

Co-authored-by: fruch <340979+fruch@users.noreply.github.com>

Author: Copilot

cassandra/io/libevreactor.py

@@ -232,19 +232,9 @@ def _atexit_cleanup():
     This wrapper ensures that cleanup receives the actual LibevLoop instance
     instead of None, which was the value of _global_loop when the module was
     imported.
-    
-    It also explicitly stops the event loop before cleanup to ensure the loop
-    breaks cleanly even if it's in the middle of processing events.
     """
     global _global_loop
     if _global_loop is not None:
-        # Stop the event loop before cleanup (thread-safe via async watcher)
-        if _global_loop._loop:
-            try:
-                _global_loop._loop.stop()
-            except Exception:
-                # If stop fails, continue with cleanup anyway
-                pass
         _cleanup(_global_loop)
 
 

cassandra/io/libevwrapper.c

@@ -6,7 +6,6 @@
 typedef struct libevwrapper_Loop {
     PyObject_HEAD
     struct ev_loop *loop;
-    ev_async async_watcher;
 } libevwrapper_Loop;
 
 static void
@@ -31,26 +30,12 @@ Loop_new(PyTypeObject *type, PyObject *args, PyObject *kwds) {
     return (PyObject *)self;
 };
 
-static void async_stop_cb(EV_P_ ev_async *w, int revents) {
-    ev_break(EV_A_ EVBREAK_ALL);
-}
-
-static PyObject *
-Loop_stop(libevwrapper_Loop *self, PyObject *args) {
-    ev_async_send(self->loop, &self->async_watcher);
-    Py_RETURN_NONE;
-}
-
 static int
 Loop_init(libevwrapper_Loop *self, PyObject *args, PyObject *kwds) {
     if (!PyArg_ParseTuple(args, "")) {
         PyErr_SetString(PyExc_TypeError, "Loop.__init__() takes no arguments");
         return -1;
     }
-    ev_async_init(&self->async_watcher, async_stop_cb);
-    ev_async_start(self->loop, &self->async_watcher);
-    // Prevent async_watcher from keeping the loop from returning
-    ev_unref(self->loop);
     return 0;
 };
 
@@ -71,7 +56,6 @@ Loop_unref(libevwrapper_Loop *self, PyObject *args) {
 static PyMethodDef Loop_methods[] = {
     {"start", (PyCFunction)Loop_start, METH_NOARGS, "Start the event loop"},
     {"unref", (PyCFunction)Loop_unref, METH_NOARGS, "Unrefrence the event loop"},
-    {"stop", (PyCFunction)Loop_stop, METH_NOARGS, "Stop the event loop from any thread"},
     {NULL} /* Sentinel */
 };