On 11:05 am, p.may...@imperial.ac.uk wrote: >On 20/02/12 20:32, Glyph wrote: >>Well, it depends on how you define a "bug". LoopingCall's internal >>state remains consistent, but if you set your clock backwards, >>LoopingCall won't fire your callback again until the system clock >>catches up to where it previously was. Any new LoopingCalls that are >>created will work fine, although they will probably report an >>incorrect skipCount if you set the clock forward again. > >Ah. This doesn't jump out from the original ticket text; the way I read >the text, it implies the LoopingCall stops being *scheduled* if the >clock goes backwards. > >If I'm understanding it correctly, the problem is actually that the >callLater for the next run doesn't fire when expected, because it's >scheduled in the "pre-change" timeframe (now the future). As opposed to >being anything in the LoopingCall code? > >I realise this is tricky to solve, but I'll note it's not impossible >for >really REALLY big clock skews to happen. For example: recently we had a >server kernel panic and need a cold reboot. The machine booted and read >it's time from the CMOS clock, which was way WAY out. A minute or two >after the machine had booted, NTP slewed the clock back by months... >Fortunately this box doesn't run any Twisted code that a) starts on >boot >and b) makes use of LoopingCall.
I've fixed this problem before by ensuring ntp gets to run before other time-sensitive services get to start. Jean-Paul >[I know this is horrible, but a lot of Unix distros don't sync system >to >hardware clock periodically - usually on shutdown only - and a lot of >distros don't block boot until NTP has set the clock] > >I realise it's an edge case; but at the very least, it is probably >worth >updating the LoopingCall/IReactorTime.callLater documentation to make >this behaviour clear, because I certainly didn't appreciate this could >occur. It's pretty obvious in hindsight, though. > >_______________________________________________ >Twisted-Python mailing list >Twisted-Python@twistedmatrix.com >http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python _______________________________________________ Twisted-Python mailing list Twisted-Python@twistedmatrix.com http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python
