> Le 21 janv. 2015 à 07:18, Terje Mathisen <terje.mathi...@tmsw.no> a écrit : > > Mike S wrote: >> The real problem is systems (POSIX, particularly), which incorrectly >> handle time, despite having over 40 years to get it right. They try to >> please everyone, while pleasing no one. POSIX tracks and does >> calculations on determinate intervals (seconds since 1/1/1970, and every >> minute has 60 seconds), and also tries to handle civil time, which has >> indeterminate intervals (unpredictable 61 second minutes). So it fails >> by trying to do two mutually exclusive things. > > Right, POSIX is neither UTC nor TAI: It is mostly a calendar device! > > POSIX is really measuring day numbers, but using a counter which is scaled by > 86400. This means that on any day with a leap second, it is not really using > SI seconds as the time base. >> >> It's not a particularly difficult problem to solve (timezone info is >> regularly updated because of civil changes, historical leap seconds >> could be, too), but requires thought about whether specific future >> events should be considered as intervals or absolute time values. > > Since there is no way to know about leap seconds several years into the > future, forward POSIX timestamps must always be considered as absolute > references. They should never be used for time intervals, even if that is the > (by far) most common use today. :-(
And one of the reasons why a significant portion of the computing community wants to get rid of leap seconds. A coverup for bad engineering practices. > > Terje > > -- > - <Terje.Mathisen at tmsw.no> > "almost all programming can be viewed as an exercise in caching" > > _______________________________________________ > questions mailing list > questions@lists.ntp.org > http://lists.ntp.org/listinfo/questions _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
