From: Rob Pike <robpike@gmail.com>
To: Douglas McIlroy <douglas.mcilroy@dartmouth.edu>
Cc: TUHS main list <tuhs@minnie.tuhs.org>
Subject: Re: [TUHS] run commands at login in v6 and stty
Date: Mon, 28 Feb 2022 18:22:28 +1100 [thread overview]
Message-ID: <CAKzdPgw3F9snv-kO+tE=rE2Q_wh_7AKxVaZ9gXFoCxaX6pgBkA@mail.gmail.com> (raw)
In-Reply-To: <CAKH6PiVCk6gSv-WVztRUiJrOt3QHVi1pCVEKzw1RcEi+m+G=bw@mail.gmail.com>
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Plan 9 had the distinct advantage of a constant system interface at the
source level. X11 did not, but it also made essentially no attempt to
abstract it away, so the lines starting #ifdef often outnumbered the actual
code. I couldn't make hide nor hair of it, and had no way to reliably test
any change.
C with #ifdefs is not portable, it is a collection of 2^n overlaid
programs, where n is the number of distinct #if[n]def tags. It's too bad
the problems of that approach were not appreciated by the C standard
committee, who mandated the #ifndef guard approach that I'm sure could
count as a provable billion dollar mistake, probably much more. The cost of
building #ifdef'ed code, especially with C++, which decided to be more
fine-grained about it, is unfathomable.
Google alone might well count for many millions of dollars in wasted
compilation equipment. I remember giving a Plan 9 demo to someone soon
after I got to Google. None of the features of the system were of interest.
The thing that astounded my audience was the ability to build the kernel on
a P90 in 20 seconds or so, and the window system in under 3. At that time,
a build of a Google server would require hours on a large distcc cluster.
I still shudder to think of it. It's worse now, of course, far worse, but
Google has far larger clusters to handle it and some improvement in
tooling. However, the #ifdefs persist.
Tom Cargill warned Bjarne about this around 1984, but the plea fell on deaf
ears.
-rob
On Mon, Feb 28, 2022 at 12:07 PM Douglas McIlroy <
douglas.mcilroy@dartmouth.edu> wrote:
> > The X11 tree was a heavily ifdef-ed. And it needed to be, I don't have
> > an answer as to how you would reuse all that code on different hardware
> > in a better way.
>
> Plan 9 did it with #include. The name of the included file was the same for
> every architecture. Only the search path for include files changed. Done
> with
> care, this eliminates the typical upfront #ifdefs.that define constants
> and set
> flags.
>
> Other preprocessor conditionals can usually be replaced by a regular if,
> letting
> the compiler optimize away the unwanted alternative. This makes
> conditionals
> obey the scope rules of C.
>
> Doug
>
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next prev parent reply other threads:[~2022-02-28 7:24 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-28 1:04 Douglas McIlroy
2022-02-28 7:22 ` Rob Pike [this message]
2022-02-28 14:07 ` Larry McVoy
2022-02-28 18:47 ` Dan Cross
2022-02-28 19:25 ` Dan Cross
2022-02-28 21:25 ` markus schnalke
2022-02-28 19:26 ` Clem Cole
2022-02-28 20:03 ` Adam Thornton
2022-02-28 18:18 ` Warner Losh
-- strict thread matches above, loose matches on Subject: below --
2022-02-27 7:48 Noel Chiappa
2022-02-26 21:45 Brian Walden
2022-02-26 22:16 ` Rob Pike
2022-02-27 20:32 ` Sven Mascheck
2022-02-26 20:39 Will Senn
2022-02-26 21:03 ` Michael Kjörling
2022-02-26 22:49 ` Clem Cole
2022-02-26 23:12 ` Rob Pike
2022-02-27 0:46 ` Clem Cole
2022-02-27 15:01 ` Larry McVoy
2022-02-27 17:10 ` Clem Cole
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