[pacman-dev] [RFC] pactree rewrite in C

[Xavier Chantry]

On Mon, Oct 11, 2010 at 3:32 PM, Dan McGee <dpmcgee at gmail.com> wrote:
> On Mon, Oct 11, 2010 at 8:06 AM, Dave Reisner <d at falconindy.com> wrote:
>> The recent patchwork over the weekend inspired me to take a closer look
>> at pactree. My first impression was that it would be a great candidate
>> for a rewrite in C.
>>
>> http://www.github.com/falconindy/pactree
>>
>> Results are entertaining:
>>
>> # bash version
>> $ time pactree -r glib2 >/dev/null
>>
>> real    0m2.538s
>> user    0m1.593s
>> sys     0m0.435s
>>
>>
>> # C rewrite
>> $ time ./pactree -r glib2 >/dev/null
>>
>> real    0m0.016s
>> user    0m0.007s
>> sys     0m0.009s
>>
>>
>> I'm finding that it's even slightly more accurate than the bash version
>> WRT to reverse dependency tracking as it's hooking into alpm's
>> alpm_pkg_compute_required_by() instead of wandering through the file
>> hierarchy.
>>
>> It's feature complete compared to the Bash version, aside from the
>> export to graphviz. The only functional change I've made is: when
>> walking reverse depends, don't re-walk already visited dependencies. I
>> thought this was a logical change given the behavior of the standard
>> dependency tracking.
>>
>> I'm happy to offer this up for merging if desirable. There's a few ugly
>> bits in the code I still want to refactor -- if anyone has any comments
>> or criticisms, they're very welcome.
>
> Didn't look at the code yet, but:
> 1. Tools that look at the database directly are bound to be broken in
> the near future anyway- some of this stuff is going to get redone, so
> we should be doing all interaction via libalpm.
> 2. As far as graphviz/dot, I think the feature would be more
> interesting anyway if it just generated the graphviz input rather than
> actually invoking graphviz. That should be easy to implement.
>
> So I at least give a +1 to this, and we can move it into src/util/
> like vercmp to make it easier to build and such.
>

This looks awesome.

Here is my benchmark :
pactree -r glibc :
1m37.494s -> 0m0.329s

Also the -r output deals correctly with providers.

The only drawback I could find is that arguments cannot be providers.
[xavier at xps-m1530 pactree (master)]$ pactree cron
+--dcron provides cron
   |--glibc
      |--linux-api-headers
      |--tzdata
[xavier at xps-m1530 pactree (master)]$ ./pactree cron
error: package 'cron' not found

Anyway Dave, it would be great if you could integrate this in
src/utils, have a look at Makefile.am for the defines you can re-use
(dbpath and/or config). Maybe you can keep it simple and just use
DBPATH as I did in testdb.

And as a bonus, keep generation of graphviz input file (or similar
graph tool) and provider feature :)