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

[Rob Seaman]

On Dec 29, 2016, at 1:35 PM, Warner Losh 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.

Let’s back that up. During the  period, approximately 15 years long, that a small faction sought to have the ITU redefine UTC, Mac OS X has lived its entire lifecycle. Sixteen years ago, Mac OS 9 was a completely different beast. For that matter, iOS and Android are both less than a decade old.

In the coming decade, one is confident that lots of other software will be written and rewritten. It will be better software if it acknowledges factual reality as its underpinning.


>> 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.

Steve Allen and some others here from the astronomy community may be amused to have such a statement directed to a long time member of astronomy's IRAF group.

POSIX dates to 1988, about the time I joined the IRAF group, though I had coded in IRAF starting around 1984. IRAF is layered on a virtual OS / kernel architecture and is coded in a highly portable C-like preprocessor language. The verbatim source runs (or ran) on various flavors of Unix, on VMS, on Data General’s OS. The code base is roughly of the scale of Linux.

As IRAF’s Y2K tsar I understand how old code can be updated to support a new timekeeping API.

Astronomy’s FITS image / table data format also predates POSIX, by an additional five years or so (late 1970s). This is a quirky international standard with a rather arcane process for changing the standard. Steve and I and likely others here are members of various FITS committees that navigate proposed changes. A checksum proposal was adopted into the standard this year that I introduced in 1994. The FITS world coordinate paper on time that Steve coauthored took a lightning fast decade or so.

Over the next decades we likely all believe that time and timekeeping will become more important, not less. As such, software and systems and standards relating to time will benefit from attacking the issues head on. At the very least preserve the current UTC standard for backwards compatibility while having some committee of the ITU or BIPM design (or attempt) a better mousetrap.


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

Time is plural. Time is more than one thing. In particular time of day and interval time are not the same thing. These things exist independently of human notions. Seek to describe them as they are, not as bureaucracies deem them to be. 


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

The current UTC standard has a lot of flexibility regarding scheduling. It is a means to an end. By all means debate ways to improve the logistics of its realization of mean solar time.


> 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.

We are doing that already. The GPS time scale exists because pragmatic engineers decided to solve the problem in front of them. Many others use TAI, but more don't because plans for improved support similar to the Torino TI resolution were subject to foot dragging while a small faction sought circularly to redefine UTC to remake it into the equivalent of TAI. This has never been about improving access to interval time, it has been about denying access to solar time.

Time of day is a different problem than interval time. Geophysics exists.

Rob

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