Suppress CancelledError in zwave-js unload #91222
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Hey there @home-assistant/z-wave, mind taking a look at this pull request as it has been labeled with an integration ( Code owner commandsCode owners of
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| @@ -792,7 +793,11 @@ async def disconnect_client(hass: HomeAssistant, entry: ConfigEntry) -> None: | |||
| for task in platform_setup_tasks: | |||
| task.cancel() | |||
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| await asyncio.gather(listen_task, start_client_task, *platform_setup_tasks) | |||
| tasks = (listen_task, start_client_task, *platform_setup_tasks) | |||
| await asyncio.gather(*tasks, return_exceptions=True) | |||
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If return_exceptions is not set to True, then asyncio.CancelledError is raised and other tasks are not awaited.
The change here ensures that:
- all tasks are awaited, even if one raises an exception
asyncio.CancelledErrorexception is ignored- other exception are still raised if they occur - but only after all tasks have been awaited
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The docs says that a task that is canceled won't stop the other tasks from being awaited in gather.
https://docs.python.org/3/library/asyncio-task.html#asyncio.gather
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But whilst the other tasks can still be awaited, they are no longer tracked by the gather, won't be cancelled nor awaited by default, will continue to run and may fail in the future.
the first raised exception is immediately propagated to the task that awaits on gather(). Other awaitables in the aws sequence won’t be cancelled and will continue to run.
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Maybe it's more effective to store the gather task and await it in a loop while suppressing CancelledError, until the gather task is done? That way we don't need to loop over all submitted tasks again after they have been awaited with gather.
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I'm interpreting the docs to say that the gather task will still track the submitted tasks if one of them raises CancelledError, since the gather task is not cancelled. Ie, we can await the gather task again if needed.
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Yes. I just ran some tests with a couple of failing task (one after 1s, one after 2s). On first gather, it will wait 1s and then raise the exception:
- task1 is done
- task 2 is still running
- gather is done
Subsequent calls to gather do not wait for the second task, but simply raise again the failure from task1
I couldn't find a way to wait for the "remaining tasks"
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Maybe you want to do asyncio.wait with ALL_COMPLETED?
https://docs.python.org/3/library/asyncio-task.html#asyncio.wait
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Using await asyncio.wait(tasks) is the same as asyncio.gather(*tasks, return_exceptions=True)
It comes down to error tracking:
- do we want to ignore only CancelledError?, and raise if there was a different error?
- or do we want to ignore all errors?
If we want to ignore all errors, then we can do away with the loop.
If we want to check which errors are not CancelledError, then we need the loop anyway.
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Let's keep it like this for now. We can improve it with TaskGroup when 3.11 is minimum Python version.
https://docs.python.org/3/library/asyncio-task.html#asyncio.TaskGroup
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We should probably log any exception with a trace.
We could log CancelledError at debug level with a trace as well in case we find a case where cancelation is happening unexpectedly... but that might be do to the cancellation semantics of asyncio.wait_for if its used anywhere in the libs which is thankfully fixed in cpython 3.12 python/cpython#98518
Proposed change
Spotted in #90850
Type of change
Additional information
Checklist
black --fast homeassistant tests)If user exposed functionality or configuration variables are added/changed:
If the code communicates with devices, web services, or third-party tools:
Updated and included derived files by running:
python3 -m script.hassfest.requirements_all.txt.Updated by running
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