How to ensure monotonic nondecreasing time
Posted Nov 29, 2006 17:19 UTC (Wed) by giraffedata
In reply to: How to ensure monotonic nondecreasing time
Parent article: Counting on the time stamp counter
I guess zooko alluded to leap seconds, where UTC stands still for
(actually: jumps backwards by) a second.
Ah. That's probably it.
Except that UTC does not stand still or go backwards. When there's a leap second, UTC goes steadily forward from 23:59:59 to 23:59:60 and then to 00:00:00. Note that a UTC time of day is a tuple of numbers (year, month, day, hour, minute, second).
But the standard Linux time representation (a single number) does step backward at leap second time; it's defined that way to make it easy to compute UTC from it.
And I think zooko's statement that a programmer can't have a time that is both monotonically nondecreasing and correlates to a human time standard has to be qualified to the case that the time is represented by a single number. As long as you're willing to work with multiple numbers, two obvious ways are TAI + delta as you suggest, and just plain UTC.
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