Subj : Re: Operating Systems
To   : Digital Man
From : tenser
Date : Wed Apr 17 2024 02:43 am

On 12 Apr 2024 at 11:29a, Digital Man pondered and said...
 
 DM>   Re: Re: Operating Systems
 DM>   By: tenser to claw on Sat Apr 13 2024 02:39 am
 DM> 
 DM>  > There's a lot of software out there, written 20 or 30 years
 DM>  > ago, that made a lot of assumptions about the state of the
 DM>  > world; there were a lot of programmers who thought to
 DM>  > themselves in 1991, "Gee, the year 2038 is a long time from
 DM>  > now..." and took shortcuts.
 DM> 
 DM> Speaking for myself at least, I started using time_t types for storing
 DM> dates and times in C programs in 1988 and wasn't even aware that it
 DM> would ever roll-over (go negative) at any point. I don't think I
 DM> actually realized that most time_t's are signed (can go negative) and
 DM> that for those systems (C libraries), dates before Jan-1-1970 are
 DM> *suppoosed* to representable in that way (as negative valeus). [libraies
 DM> that use unsigned time_t's cannot represent dates before Jan-1-1970] And
 DM> I'm pretty sure it was 1992 when I did the math and realized that 2038
 DM> and 2106 are going to be problematic years for 32-bit time_t-based
 DM> libraries/programs. It was certainly not discussed in the programming
 DM> books or among C programmers of the era. We weren't taking shortcuts, we
 DM> were just following the norms. Use of 64-bit integers for most things
 DM> seemed excessive/wasteful and in many environments (e.g. 16-bit systems)
 DM> not practical or even possible. -- 

Using time_t was less the "shortcut" issue that I was thinking
of, and more people doing things like casting back and forth
between various int types.  Disciplined use of `time_t`, and
not making a lot of assumptions about size of that type, makes
the problem tractable in programs for which one has the source.

The VMS people warned us about this a long time ago; certainly
in the 80s.  DEC engineering famously had a bug that they kept
open that said something like, "VMS dates won't work after the
year 9999."

I distinctly remember people talking about 2038 in the runup
to Y2K and the consensus was mostly, "meh, we'll fix it before
then."  In the 32-bit era, we had more pressing issues, like
running out of address space, or the UID space rolling over on
big installations.

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