New submission from STINNER Victor: Hi, while comparing performances of Tulip and Trollius projects (asyncio module), I found a bug. The event loop is called too many times when a callback is scheduled with a timeout and the epoll selector is used, especially for timeout close to one millisecond.
In my opinion, it's a bug in epoll.poll(): it should wait *at least* timeout seconds if no event is received, not shorter. Pseudo-code of Tulip: --- timeout = scheduled[0].when - time.monotonic() events = selector.select(timeout) process_events(events) while scheduled: if scheduled[0].when > time.monotonic(): break ... --- The problem is that "scheduled[0].when > time.monotonic()" test fails because epoll.poll() returns in less than timeout seconds. The difference between the timeout and elapsed time is very small, less than 1 millisecond. Attached patch fixes this issue by rounding the timeout to the upper bound. The rounding is different than datetime.timedelta constructor for example, because the usecase is different. epoll.poll(0.0001) calls epoll_wait() with a timemout of 1 millisecond (1e-4 rounded to 1e-3). epoll.poll(0.0) still calls epoll_wait() with a timeout of 0 millisecond. I don't think that it's possible to write a reliable unit test for that on our slow buildbots. ---------- files: epoll_timeout.patch keywords: patch messages: 208532 nosy: gvanrossum, haypo, neologix, pitrou, serhiy.storchaka priority: normal severity: normal status: open title: epoll.poll(timeout) must round the timeout to the upper bound versions: Python 3.3, Python 3.4 Added file: http://bugs.python.org/file33563/epoll_timeout.patch _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue20311> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com