A Darren Dunham
ddunham at taos.com
Fri Jul 1 17:14:56 UTC 2011
On Fri, Jul 01, 2011 at 09:43:49AM -0700, Guy Harris wrote:
> > Actual computer systems may follow this. Or they may alter the speed of
> > their internal clock to slew them back into sync with the value of time_t,
> > just as they do when they discover an error in their internal clock.
> ...or they may fail to do either, and thus, in practice, violate
> POSIX. I suspect that, these days, NTP is used enough that they do
> arrange that time_t not tick exactly once per SI second (yeah, one
> could view that as "NTP is not only used to *correct* clock drift,
> it's also used to *cause* clock drift as required by POSIX").
NTP doesn't have a table of leap seconds (or even much knowledge about
them ahead of time), so the clock isn't slewed or modified ahead of a
leap second insertion.
Some computers have (non-POSIX) interfaces to allow NTP to either insert
a second or pause the clock for a second. Many computers have neither
and NTP simply corrects the clock afterward as if it were off by one
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