New submission from Ben Darnell <ben.darn...@gmail.com>:
Proactor and selector event loops behave differently when call_soon_threadsafe races with a concurrent call to loop.close(). In a selector event loop, call_soon_threadsafe will either succeed or raise a RuntimeError("Event loop is closed"). In a proactor event loop, it could raise this RuntimeError, but it can also raise an AttributeError due to an unguarded access to self._csock. https://github.com/python/cpython/blob/1ed61617a4a6632905ad6a0b440cd2cafb8b6414/Lib/asyncio/proactor_events.py#L785-L787 Comments in BaseSelectorEventLoop._write_to_self indicate that this is deliberate, so the `csock is not None` check here should probably be copied to the proactor event loop version. https://github.com/python/cpython/blob/1ed61617a4a6632905ad6a0b440cd2cafb8b6414/Lib/asyncio/selector_events.py#L129-L136 I'd also accept an answer that the exact behavior of this race is undefined and it's up to the application to either arrange for all calls to call_soon_threadsafe to stop before closing the loop. However, I've had users of Tornado argue that they use the equivalent of call_soon_threadsafe in contexts where this coordination would be difficult, and I've decided that tornado's version of this method would never raise, even if there is a concurrent close. So if asyncio declines to specify which exceptions are allowed in this case, tornado will need to add a blanket `except Exception:` around calls to call_soon_threadsafe. ---------- components: asyncio messages: 362078 nosy: Ben.Darnell, asvetlov, yselivanov priority: normal severity: normal status: open title: Exceptions raised by EventLoop.call_soon_threadsafe versions: Python 3.8 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue39651> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com