Re: ‘core-updates’ is back!

[ludo@gnu.org (Ludovic Courtès)]

Andy Wingo <wingo@igalia.com> skribis:

> On Tue 29 Aug 2017 00:01, ludo@gnu.org (Ludovic Courtès) writes:
>
>> Yup, I just created a new ‘core-updates’ branch by pushing
>> <https://bugs.gnu.org/27849>.  Enjoy!
>>
>> Let’s freeze in one month, say Oct. 1st?
>
> It would be pretty cool if we could fix our O(n^2) problems in search
> paths in this core-updates -- basically whenever you go to create an
> environment, instead of making e.g. VAR=A:B:C:..., for all VARs
> (LIBRARY_PATH, PKG_CONFIG_PATH, etc), instead we make a union directory
> Z containing the union of A, B, C, etc and set VAR=Z.  The goal would be
> to fix quadratic run-time lookup costs by replacing it with a
> compile-time computation.  This applies to many lookups: PATH, -rpath,
> etc.

A possible alternative solution for ld.so is at
<https://bugs.gnu.org/26048>.

I’m not entirely sure about the idea of creating union directories
everywhere.  A problem is that we’d be retaining lots of union
directories, and even if they’re cheap, that could become non-negligible
(for every package we’d have to download/build an extra derivation).  It
would also add an extra level of symlinks to go through when one is
debugging things.  Also, some tools might not notice that
/abc…/lib/libfoo, /def…/lib/libfoo, and /123…/lib/libfoo actually are
the same thing.

Thoughts?

Ludo’.