Guido van Rossum added the comment: Honestly, I've lost track of the queue design. Maybe the push-back on cancellation is just wrong? After all, if a coroutine has received an item, it's out of the queue, even if it gets cancelled before it can do anything with the item.
On Thu, Aug 6, 2015 at 8:19 PM, Yury Selivanov <rep...@bugs.python.org> wrote: > > Yury Selivanov added the comment: > > Guido, Victor, > > I've just pushed a commit to fix a misspelled method call in queues.py > (related to the previous commit in this issue). > > Along with fixing the bug and writing a unittest for it, I discovered an > issue with the current queues design. > > Here's an outline of the new unittest: > > 1. we have a queue with three queue.get() coroutines waiting for its > items: `g1`, `g2`, `g3` > > 2. we do `push_nowait(i1)` and `push_nowait(i2)`; we cancel `g1` > > 3. the loop gets the chance to run > > 4. `g1` detects that it was cancelled and pushes the item `i1` in front of > the queue (otherwise we just lose it). > > Now, the problem is that `g2` has already received `i2` (by > `push_nowait`); and `i1` will end up consumed by `g3`! > > This all means that with getter coroutines being cancelled, it's possible > that getters might receive queue items out of order. > > So the question is: is this a matter of documenting this behaviour, or we > should consider some other design for queues implementation? > > ---------- > > _______________________________________ > Python tracker <rep...@bugs.python.org> > <http://bugs.python.org/issue23812> > _______________________________________ > ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue23812> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
