Path: utzoo!utgpu!water!watmath!clyde!rutgers!ames!amdahl!chongo
From: chongo@amdahl.amdahl.com (Landon Curt Noll)
Newsgroups: comp.bugs.4bsd
Subject: Re: ctime(3) and leap seconds :-(
Keywords: ctime, leap second, epoch
Message-ID: <20697@amdahl.amdahl.com>
Date: 12 Jan 88 19:50:29 GMT
References: <604@PT.CS.CMU.EDU> <6976@brl-smoke.ARPA> <20532@amdahl.amdahl.com> <175@wundt.psy.vu.nl> <1964@rti.UUCP>
Reply-To: chongo@amdahl.amdahl.com (Landon Curt Noll)
Organization: Amdahl Coup, UTS Products Hen House
Lines: 45

In article <1964@rti.UUCP> trt@rti.UUCP (Thomas Truscott) writes:
 >Yes, 14 secs one way or another is no big deal.
 >So you won't care if someone fixes the leap-second bug in ctime, right?

And by the same logic, you won't care if we all don't fix it, right?

 >DO NOT ATTEMPT TO FIX THE BUG BY DOCUMENTING IT!
 >We might document "ignore leap seconds" but that results in
 >small but very real errors that someday could cause real harm.

But there exists software that would dislike to see: 23:59:60.  That is an
example of real harm NOW if we require a change or leave open the choice 
to vendors.

If you leave it up to the vendors to fix or not fix time based on leap
seconds, then you could be faced with synced machines on a localarea net
converting into or out of timestamps differently.  The 14 seconds
between synced machines could be a non-trivial difference.  Since the
Earth is unlikely to obtain a boost of rotational energy, this
difference is likely to increase in the future.  :-)

Or consider two machines from two different vendors:

	Vendor DOES			Vendor DOESNOT
	-----------			--------------
	keeps track of leap seconds	does not keep track of leap seconds

If I ask 'DOES' and 'DOESNOT' to give me the string produced by
asctime(gmttime(some_fixed_timestamp)), I could get different values!
If I ask them to convert the same ascii time string (assume it is GMT
based time) into a timestamp, I could get different values!

We have 3 main choices:

	1) leave the timestamp conversion alone  (>99% don't do leap seconds)
	2) force systems to do leap seconds (a change with doubtful value
	      transition problems and retroactive change problems)
	3) allow systems to select their option (problems with synced systems)

I vote for #1.

chongo <> /\oo/\
-- 
[views above shouldn't be viewed as Amdahl views, or as views from Amdahl, or
 as Amdahl views views, or as views by Mr. Amdahl, or as views from his house]