[LEAPSECS] POSIX? (was Time math libraries, UTC to TAI)

[Warner Losh]

On Thu, Dec 29, 2016 at 9:42 PM, Rob Seaman <seaman at lpl.arizona.edu> wrote:
> On Dec 29, 2016, at 1:35 PM, Warner Losh <imp at bsdimp.com> wrote:
>
>>> A lot of code could have been changed while the ITU fiddled, e.g., Mac OS X
>>> was launched in 2001.
>>
>> Could have, but didn’t...
>>
>> Of course, MacOS is largely based on legacy code...
>
> Sixteen years ago, MacOS was a completely different operating system than on this MBP.
>
> The issue is what happens over the next fifteen years.

That's not even remotely true. The GUI is completely different, but
the core of the OS hasn't been rewritten in the past 15 years.

> The argument appears to be that POSIX is such crap that we have to degrade other technologies. This may be aligned with the zeitgeist of 2016, yet remains oddly unpersuasive.

It's only unpersuasive because you don't understand how long old code
sticks around.

>>>> UTC may well be superior to POSIX's notion, but that’s entirely besides the point.
>>>
>>> It is the only point.
>>
>> It all depends on the metrics you use to judge it by.... Is time of day more important or interval time more important.
>
> Reject the premise. Time of day is mean solar time. Interval time is atomic time.

Right, you just use different metrics than I. Our understanding and
notion of time has evolved, and continues to evolve.

> Both exist in the physical universe we inhabit. Systems should be engineered to handle both. Leap seconds are a means to an end, and UTC remains a reasonable compromise, but by all means seek another compromise.

Yes. There are ways to improve UTC such that it can actually be more
reliably implemented in software by making its irregularities more
predictable.

>> You've obviously never dealt with pervasive standards in coding that date back to the 70's that are nearly impossible to change. Doing that by fiat isn't going to work.
>
> Or one could point out that time of day has been mean solar time since the big bang (well, since the first roughly spherical protoplanet formed a solid crust). That’s an awfully big windmill at which to tilt.
>
>
>>> Or simply adopt GPS or TAI
>>
>> Won't work. Been proposed and rejected many times.
>
> I did mention:
>
>>> Commercial devices already exist…that implement high precision GPS and TAI.
>
> The ones we have run Linux. (Discussions of whether Linux is POSIX are redirected to /dev/null.)
>
> POSIX wants to pretend that time of day is interval time. If so, just don’t call it “Universal Time”.

You did mention them. I'll note that while one can run with TAI or GPS
time, and one has been able to do that for at least 20 years that I'm
aware of, it doesn't solve the problem. If it was that easy, we'd be
doing it already.

Warner