WITH_HASH_MAP

[Panu Matilainen]

On Wed, 28 Jun 2006, Ralf Corsepius wrote:

> Hi,
>
> apt-pkg/rpm/* contains a conditionally compiled code using a define
> named WITH_HASH_MAP.
>
> AFAIS, this seems to be an incomplete attempt to use hash_map<> instead
> of map<> for some kind of dictionary operations.
>
> ATM, WITH_HASH_MAP is never defined, so the code will never be compiled
> nor used.

Did a bit of digging into the cnc svn repository... it was originally 
added here as a configure option --with-hashmap:
svn diff -r77:79 https://oops.kerneljanitors.org/repos/apt-rpm/trunk

It's then later (-r116:117 from the repo above) converted to be 
autodetected and always used if ext/hashmap is present... or supposed to: 
the define changes from WITH_HASH_MAP to WITH_GNU_HASH_MAP but the change 
is not done (by mistake I believe) to all the places, making it 
non-functional.

>
> Question: What to do?
>
> If we want to get this functional, we should at least add some magic
> corresponding magic to the configure script to activate this code.
> If we don't want to get this functional, I'd be in favor of eliminating
> this "dead code".
>
> Subquestions, I currently can't answer:
>
> * Would be using hash_map<>'s be worth it?
> Generally speaking, my attitude on them is ambivalent: On one hand, they
> are non-portable, tedious to use and an additional source of errors, but
> promise a speed up. Is such a speed up sensible/measurable in these
> particular cases? I don't know.
>
> * Would be keeping the current implementation of hash_map<> support be
> worth it?
> IMO, the current implementation is problematic (to say the least).
> I do not think keeping it is worth it.
>
> For the moment, I'd propose to add another option to configure (say
> --enable-experimental), which would optionally compile apt with
> "WITH_HASH_MAP". We'd then pretty soon know if this code is functional
> at all, and if it provides a measurable speed up.

All that's needed is s/WITH_HASH_MAP/WITH_GNU_HASH_MAP/ in the rpm 
directory to resurrect the thing that's supposed to have been enabled all 
these years (been unused since March 2003).

So re-enabling it is trivial enough, profiling whether it actually buys us 
anything is another thing. The comments in svn say "provides good speed 
improvement" but... I'll try to have a look at it tomorrow along with 
various other things.

 	- Panu -