Poul-Henning Kamp replies to Markus Kuhn:
> No. The leapsecond support, like any other operating facility
> examine and reject illegal data.
>
> Leapseconds and *defined* as happening on midnight at the end of a
> month and the operating system should not allow them anywhere else.
I was reminded once that there is no good or bad karma, only karma.
There are no illegal data - only data. As we are seeing, what is
illegal today may be legal tomorrow - or the reverse. Definitions
can change; well written software takes this into account.
> The kernel restricts itself to checking the midnight part, and that
> is a sensible shortcut.
This is not a shortcut. This is the implementation of a design
requirement. A layered design like NTP should, and apparently does,
introduce only those restrictions into each interface that are
strictly required. If a requirement is to "reject illegal data",
those data should typically be rejected only by the externally
visible layers of the system.
> this is only economically feasible in very critical systems.
Economics is the "dismal science". If there is any validity at all
to describing it as a science, inferences must be based on coherent
experimental design. Where is the evidence that ceasing leap seconds
won't be more expensive than continuing them? Should this not be
part of any viable proposal?
It also doesn't seem to be a winner of an argument to point out that
the proposal seeks to benefit "not very critical" systems.
> And from a testing point of view, the UNIX computers are almost the
> smallest bits, it's all the weird crap people connect to them that
> makes testing a problem.
Ah yes! The ITU proposal seeks to benefit "weird crap", too. I
don't recall seeing that mentioned. Certainly no reason to expect
that devices attached to computers be governed with similar
professionalism as the computers themselves.
>> Incompetent test design is an orders of magnitude heavier stone...
>
> Ohh, I fully agree, but that doesn't justify forcing a basically
> untestable concept like leap seconds on the morons.
So "leap second users" are no longer simply world citizens, now they
are to be regarded as morons? That'll go over big in front of a
Congressional subcommittee.
>> I hope this API will one day be replaced by a much simpler and
>> more generic one.
>
> We can only hope, but to do so you'd have to get buyin from at
> least [4xfooBSD, Linux, Dave Mills, Solaris, AIX] Of these Dave
> Mills is probably the harder one.
He's always seemed reasonable to me. And lots of reasonable people
will have to ultimately reinvent the delivery of GMT to support
traditional usage far afield of astronomy.
John Cowan says:
> The real problems arrive when it is impossible to pretend any
> longer that a day consists of 24 hours. When, say, every third TAI
> second is a UTC leap second, and we have to fit three sleep/wake
> cycles into two solar days, we hopefully won't be hearing quite so
> much about the vital importance of keeping civil time slaved to the
> mean Sun.
No one has ever claimed that solar time won't face a challenge in the
far future. This proposal does absolutely nothing to address these
challenges - in fact, it complicates the issues by introducing a huge
unpalatable time step that will be no more predictable than leap
seconds.
And to clarify, it isn't solar time that faces this challenge - it
will be atomic time. The Earth will continue to circle the Sun and
spin on its axis with enviable reliability. It is our simplified
model of the tick, tick, tick of time that will fall short. Civil
time will obviously continue to be synchronized to the Sun. It is
absurd to suggest that our descendants will cease to care about the
rising of the Sun. Is that a future you want for your children's
children? As I said more than four years ago (
http://iraf.noao.edu/
~seaman/leap), in the far future there are few options other than
readjusting the length of the civil second to recalibrate to match
the slowing Earth. This will obviously happen well before 8 leap
hours are needed daily (something like 1.5 billion years from now).
These are all very interesting questions. Why don't we simply drop
this silly ITU proposal and finally start discussing the fundamental
issues? It would be refreshing for the committee members to actually
respond to our messages.
Rob Seaman
National Optical Astronomy Observatory
Received on Mon Aug 01 2005 - 10:12:31 PDT