Stop raising exception on BackgroundService cancell

Cancelling BackgroundService should not raise exception.
We cancell it when we stop actor, after calling `actor.wait()`.

Signed-off-by: Elzbieta Kotulska <[email protected]>

Author: ela-kotulska-frequenz

RELEASE_NOTES.md

@@ -17,3 +17,5 @@
 ## Bug Fixes
 
 - Fixed bug with formulas raising exception when stopped.
+
+- Fix a bug that caused BackgroundService to raise exception when actor was stopped.

src/frequenz/sdk/actor/_background_service.py

@@ -6,6 +6,7 @@
 import abc
 import asyncio
 import collections.abc
+import logging
 from types import TracebackType
 from typing import Any, Self
 
@@ -251,6 +252,8 @@ async def wait(self) -> None:
                     # This will raise a CancelledError if the task was cancelled or any
                     # other exception if the task raised one.
                     _ = task.result()
+                except asyncio.CancelledError:
+                    logging.debug("Task %s has been cancelled", self.name)
                 except BaseException as error:  # pylint: disable=broad-except
                     exceptions.append(error)
             if exceptions:

tests/actor/test_actor.py

@@ -390,6 +390,6 @@ async def cancel_actor() -> None:
         (*RUN_INFO, "Actor EchoActor[EchoActor]: Starting..."),
         (*ACTOR_INFO, "Actor EchoActor[EchoActor]: Started."),
         (*ACTOR_INFO, "Actor EchoActor[EchoActor]: Cancelled."),
-        (*RUN_ERROR, "Actor EchoActor[EchoActor]: Raised an exception while running."),
+        (*RUN_INFO, "Actor EchoActor[EchoActor]: Finished normally."),
         (*RUN_INFO, "All 1 actor(s) finished."),
     ]