Rob Mueller (fastmail) wrote:
> I recently had a similar problem. A regex that worked fine in sample code
> was a dog in the web-server code. It only happened with really long strings.
> I tracked down the problem to this from the 'perlre' manpage.
>
> WARNING: Once Perl sees that you need one of "$&", "$`", or "$'"
> anywhere in the program, it
> has to provide them for every pattern match. This may substantially
> slow your program. Perl
> uses the same mechanism to produce $1, $2, etc, so you also pay a
> price for each pattern that
> contains capturing parentheses. (To avoid this cost while retaining
> the grouping behaviour,
> use the extended regular expression "(?: ... )" instead.) But if you
> never use "$&", "$`" or
> "$'", then patterns without capturing parentheses will not be
> penalized. So avoid "$&",
> "$'", and "$`" if you can, but if you can't (and some algorithms
> really appreciate them),
> once you've used them once, use them at will, because you've already
> paid the price. As of
> 5.005, "$&" is not so costly as the other two.
>
> Basically one of the modules in the web-app I was 'use'ing needed $', but my
> test code didn't 'use' that module. The result was pretty dramatic in this
> case, something that took approx 1 second in the test code was timing out
> after 2 minutes in the web-server.
>
> What I did in the end was something like this:
>
> In the code somewhere add this so it's run when a request hits.
>
> open(F, '>/tmp/modulelist');
> print F join("\n", values %INC), "\n";
> close(F);
>
> This creates a file which lists all the loaded modules. Then after sticking
> a request through the browser, do something like:
>
> grep \$\' `cat /tmp/modulelist`
> grep \$\& `cat /tmp/modulelist`
> grep \$\` `cat /tmp/modulelist`
>
> to try and track down the offending module. You'll get quite a few false
> hits (comments, etc), but you might find an offending module. The main ones
Also check Devel::FindAmpersand and Devel::SawAmpersand.
cpan> i /ampersand/
Distribution A/AN/ANDK/Devel-SawAmpersand-0.20.tar.gz
Module Apache::SawAmpersand (Contact Author The Perl/Apache
Mailing List <[EMAIL PROTECTED]>)
Module B::FindAmpersand (A/AN/ANDK/Devel-SawAmpersand-0.20.tar.gz)
Module Devel::FindAmpersand
(A/AN/ANDK/Devel-SawAmpersand-0.20.tar.gz)
Module Devel::SawAmpersand
(A/AN/ANDK/Devel-SawAmpersand-0.20.tar.gz)
5 items found
The Devel::SawAmpersand also explains a workaround for using &.
_____________________________________________________________________
Stas Bekman JAm_pH -- Just Another mod_perl Hacker
http://stason.org/ mod_perl Guide http://perl.apache.org/guide
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