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Dear members of the mod_perl list,
I did not find an elegant, robust way of checking for the mod_perl
version number. I propose an unelegant, robust way below for those
interested.
$ENV{MOD_PERL} is obviously not OK because the UNIX environment has
the wrong semantics: it can be altered in too many places for
starters, and not just from Perl (e.g. it's customary for
security-minded code to reset all of %ENV to sane values, which makes
parts of the app "forget" that they are running mod_perl). And it's
inherited in child processes, so say when Apache forks/execs a helper
written in Perl things tend to go from bad to worse.
$mod_perl2::VERSION skips these drawbacks (it can only be altered from
Perl and is not inherited) but it is currently not trustworthy either:
$ perl -Mmod_perl2 -e 'print $mod_perl2::VERSION'
2.000001
BTW this problem triggers a bug in e.g. Apache::DB when several
installations of mod_perl (1.26 and 2.000001 in my case) cohabit on
the same system (I'm sending a separate bug report to Frank Wiles).
The only reliable way of checking for mod_perl is by probing for an
"unusual" feature of the Perl runtime, say an XS sub that the core of
mod_perl provides directly. Here is the crock I'm currently using to
that effect:
sub mod_perl_version {
my @discriminating_symbols =
(2 => "Apache2::XSLoader::BOOTSTRAP",
1.99 => "Apache::XSLoader::BOOTSTRAP",
1 => "Apache::exit");
use B;
while(my ($version, $discrimsymbol) =
splice(@discriminating_symbols, 0, 2)) {
no strict "refs";
next if (! exists &{$discrimsymbol});
my $bref = B::svref_2object(\&{$discrimsymbol});
next if ( (! defined $bref) || (! $bref->XSUB()) );
return $version;
}
return undef;
}
Not exactly pretty, but robust it is: "PerlSetupEnv Off" won't derail
it, it works at every stage of the mod_perl state automaton including
early initialization, and so on.
FEATURE REQUEST: I'd love to get rid of the "use B;" crockery above, e.g.
return mod_perl::version_running() if exists
&mod_perl::version_running();
Best regards and thanks for all the great work!
- --
Dominique QUATRAVAUX Ingénieur senior
01 44 42 00 08 IDEALX
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