[PATCH 0/6] gitweb: Some mod_perl specific support (but not only)

This is series of gitweb patches to provide better mod_perl support, for now running gitweb under mod_perl's Registry, but in the future as mod_perl handler.

First patch is mod_perl related only in a way that it provides path to mod_perl specific support, but has its own advantages even when running gitweb simply as CGI script, namely the centralization of stopping output after HTTP header for HEAD requests. Till this patch only git_feed had this feature (originally by Andreas Fuchs).

Second patch was created because further patches make gitweb to have different codepath for mod_perl; so mod_perl version string was added to "generator" meta header in HTML header.

I'm not so sure about third patch, namely if I understood what is written in CGI(3pm) about compile method.

Fourth patch prepares the way for mod_perl specific support. Perhaps "our $r = shift @_;" instead of "my $r = shift @_;" would be better.

Fifth patch appears to be unnecessary, at least for now, because mod_perl Registry populates %ENV hash (and does not need to set envirionmental variables). Still, it prepares the way for future running gitweb as mod_perl handler, and not under Registry.

Sixth patch is an RFC. It tries to add HTTP headers directly, allowing Apache to not need to parse headers, which should speed up gitweb a bit. It also makes use of mod_perl meets_expectation method to respond to If-Modified-Since: and If-None-Match: requests for cache validation. Current state is a bit of mess as it is now. Comments (and patches) appreciated.

Table of contents (shortlog):
=============================
 [PATCH 1/6] gitweb: Separate HTTP header output
 [PATCH 2/6] gitweb: Add mod_perl version string to "generator" meta header
 [PATCH 3/6] gitweb: Precompile CGI routines for mod_perl
 [PATCH/RFC 4/6] gitweb: Prepare for mod_perl specific support
 [RFC/PATCH 5/6] gitweb: Make possible to run under mod_perl without SetupEnv
 [RFC/PATCH 6/6] gitweb: Make possible to run under mod_perl without ParseHeaders

Diffstat:
=========
 gitweb/gitweb.perl |  227 +++++++++++++++++++++++++++++++++++++++++++++++-----
 1 files changed, 205 insertions(+), 22 deletions(-)

Benchmarks: =========== $ ab -n 10 "http://localhost/perl/gitweb/gitweb.cgi?p=git.git;a=summary" $ ab -n 10 -c 2 "http://localhost/perl/gitweb/gitweb.cgi?p=git.git;a=summary" (hot cache)

$ ab -n 10 "http://localhost/perl/gitweb/gitweb.cgi/git.git" $ ab -n 10 -c 2 "http://localhost/perl/gitweb/gitweb.cgi/git.git" (hot cache)

patch                                         | mean +/- sd     | mean -c 2
-----------------------------------------------------------------------------
[before first patch in series]:               | 287 +/-  8.8 ms | 296.049 ms
 (path_info version)                          | 293 +/- 10.6 ms | 314.526 ms
gitweb-Separate-HTTP-header-output:           | 302 +/- 46.7 ms | 300.305 ms
gitweb-Add-mod_perl-to-generator:             | 288 +/- 15.6 ms | 306.050 ms
gitweb-Precompile-CGI-routines-for-mod_perl:  | 291 +/- 10.9 ms | 306.704 ms
gitweb-Prepare-for-mod_perl-specific-support: | 299 +/- 11.0 ms | 300.879 ms
gitweb-mod_perl-without-SetupEnv:             | 288 +/- 12.4 ms | 296.809 ms
 (path_info version)                          | 292 +/- 12.7 ms | 307.380 ms
gitweb-mod_perl-without-ParseHeaders:         | ???             | ???