Fix segfault by adding __enter__ and __exit__ to Waitable

rclpy/rclpy/executors.py

@@ -506,9 +506,6 @@ def _wait_for_ready_callbacks(
             entity_count = NumberOfEntities(
                 len(subscriptions), len(guards), len(timers), len(clients), len(services))
 
-            for waitable in waitables:
-                entity_count += waitable.get_num_entities()
-
             # Construct a wait set
             wait_set = _rclpy.rclpy_get_zero_initialized_wait_set()
             with ExitStack() as context_stack:
@@ -550,6 +547,13 @@ def _wait_for_ready_callbacks(
                     except InvalidHandle:
                         entity_count.num_guard_conditions -= 1
 
+                for waitable in waitables:
+                    try:
+                        context_stack.enter_context(waitable)
+                        entity_count += waitable.get_num_entities()
+                    except InvalidHandle:
+                        pass
+
                 context_capsule = context_stack.enter_context(self._context.handle)
                 _rclpy.rclpy_wait_set_init(
                     wait_set,

rclpy/rclpy/qos_event.py

@@ -114,6 +114,14 @@ def add_to_wait_set(self, wait_set):
         with self.__event:
             self._event_index = _rclpy.rclpy_wait_set_add_event(wait_set, self.__event)
 
+    def __enter__(self):
+        """Mark event as in-use to prevent destruction while waiting on it."""
+        self.__event.__enter__()
+
+    def __exit__(self, t, v, tb):
+        """Mark event as not-in-use to allow destruction after waiting on it."""
+        self.__event.__exit__(t, v, tb)
+
     def destroy(self):
         self.__event.destroy_when_not_in_use()
 

rclpy/rclpy/waitable.py

@@ -65,6 +65,14 @@ def __init__(self, callback_group):
         # List of Futures that have callbacks needing execution
         self._futures = []
 
+    def __enter__(self):
+        """Implement to mark entities as in-use to prevent destruction while waiting on them."""
+        pass
+
+    def __exit__(self, t, v, tb):
+        """Implement to mark entities as not-in-use to allow destruction after waiting on them."""
+        pass
+
     def add_future(self, future):
         self._futures.append(future)