New submission from Ben Mather: The documentation for the `set_running_or_notify_cancel` method on `concurrent.futures.Future` states that it will notify waiting threads and trigger callbacks after the `Future` has been cancelled, however currently this is done immediately by the call to `cancel`.
Oddly waiters (private interface used to implement `wait` and `as_completed`) do follow the behaviour documented for callbacks (they are called in `set_running_or_notify_cancel`) which means that they are not equivalent to setting a callback on each future. I have attached three possible patches: 1) "change-callbacks.patch" - this changes the behaviour to match the documentation. 2) "change-docs.patch" - this fixes the documentation to match the current behaviour. 3) "change-docs-and-waiters.patch" - in addition to fixing the documentation, this also fixes the inconsistency between waiters and callbacks by invoking waiters' `add_cancelled` method in `cancel`. I believe moving to the documented behaviour (1) would be a mistake as currently `set_running_or_notify_cancel` and the `RUNNING` state can be skipped entirely allowing Futures to be used just as a way to send results. Should mention that I have a separate patch (which I will submit separately (or here?)) that re-implements `wait` and `as_completed` using only publicly exposed methods. This makes it possible to extend or replace `Future` without having to preserve its private interface. Unfortunately this slightly breaks compatibility due to the difference between waiters and callbacks. I thought it would be best to discuss this issue first as I don't believe the current behaviour is as intended. ---------- assignee: docs@python components: Documentation, Library (Lib) files: change-callbacks.patch keywords: patch messages: 229282 nosy: bwhmather, docs@python priority: normal severity: normal status: open title: `concurrent.futures.Future.set_running_or_notify_cancel` does not notify cancel versions: Python 3.2, Python 3.3, Python 3.4, Python 3.5 Added file: http://bugs.python.org/file36908/change-callbacks.patch _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue22630> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
