On Tue, Jan 03, 2017 at 06:35:03PM +0000, Stewart Bryant wrote:
> Yes, the system should use a leap-second-free constant-duration-seconds time
> for everything. It is only humans that need the variable jumpy version of
> time presented to them, and that is a UI issue.
I don't think that's quite right.
Unix time is canonically a count of seconds since an epoch and admits no
leap seconds. A conversion of Unix time to adjusted (i.e., with leap
seconds added) time since the same epoch would be nice, as well as:
- conversion from either to broken down time
- with seconds count up to 60 when converting from seconds-with-leaps
- formatting of dates from either as well as from broken down time
- but when converting from seconds-with-leaps the formatted string
can show seconds-in-minute values of 60
- whereas when converting from Unix seconds the formatted string can
never show seconds-in-minute values of 60
- parsing to broken down time and to seconds-since-epoch types
- ignoring leap seconds when converting to Unix time
- correctly accounting for all leap seconds prior to that time when
converting to seconds-with-leaps-since-epoch
It's all about data typing. In POSIX C API terms, we need new functions
to deal with seconds-with-leaps-since-epoch, and obviously a lot of
prayer because there's no way in C to distinguish one integer type from
the other (well, the new type could be wrapped in a struct..).
We will have to deal with multiple kinds of time as long as different
applications/users need different definitions of time. Astronomers may
need corrected time, while bankers may want to ignore leap seconds --
all on the same systems (same OSes, same code libraries).
Functionally this is about data typing -- preferably strong data typing.
Smearing is a third time representation that also needs conversion to
the other types (more opportunity for bugs!); it leaves a bad taste. It
may work for some apps though, but all nodes had better smear in exactly
the same way -- within your tolerances -- if your app depends on time
for synchronization.
Nico
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