Apache::DProf - Hook Devel::DProf into mod_perl

 #in httpd.conf
 PerlModule Apache::DProf

The Apache::DProf module will run a Devel::DProf profiler inside each child server and write the tmon.out file in the directory $ServerRoot/logs/dprof/$$ when the child is shutdown. Next time the parent server pulls in Apache::DProf (via soft or hard restart), the $ServerRoot/logs/dprof is cleaned out before new profiles are written for the new children.

It is possible to profile code run under mod_perl with only the Devel::DProf module available on CPAN. You must have apache version 1.3b3 or higher. When the server is started, Devel::DProf installs an END block to write the tmon.out file, which will be run when the server is shutdown. Here's how to start and stop a server with the profiler enabled:

 % setenv PERL5OPT -d:DProf
 % httpd -X -d `pwd` &
 ... make some requests to the server here ...
 % kill `cat logs/httpd.pid`
 % unsetenv PERL5OPT
 % dprofpp

There are downsides to this approach:

- Setting and unsetting PERL5OPT is a pain.

- Server startup code will be profiled as well, which we are not really concerned with, we're interested in runtime code, right?

- It will not work unless the server is run in non-forking -X mode

These limitations are due to the assumption by Devel::DProf that the code you are profiling is running under a standard Perl binary (the one you run from the command line). Devel::Dprof relies on the Perl -d switch for intialization of the Perl debugger, which happens inside perl_parse() function call. It also relies on Perl's special END subroutines for termination when it writes the raw profile to tmon.out. Under the standard command line Perl interpreter, these END blocks are run when the perl_run() function is called. Also, Devel::DProf will not profile any code if it is inside a forked process. Each time you run a Perl script from the command line, the perl_parse() and perl_run() functions are called, Devel::DProf works just fine this way.

Under mod_perl, the perl_parse() and perl_run() functions are called only once, when the parent server is starting. Any END blocks encountered during server startup or outside of Apache::Registry scripts are suspended and run when the server is shutdown via apache's child exit callback hook. The parent server only runs Perl startup code, all request time code is run in the forked child processes. If you followed the previous paragraph, you should be able to see, Devel::DProf does not fit into the mod_perl model too well. The Apache::DProf module exists to make it fit without modifying the Devel::DProf module or Perl itself.

The Apache::DProf module also requires apache version 1.3b3 or higher and PerlChildInitHandler enabled. It is configured simply by adding this line to your httpd.conf file:

 PerlModule Apache::DProf

When the Apache::DProf module is pulled in by the parent server, it will push a PerlChildInitHandler via the Apache push_handlers method. When a child server is starting the Apache::DProf::handler subroutine will called. This handler will create a directory dprof/$$ relative to ServerRoot where Devel::DProf will create it's tmon.out file. Then, the handler will initialize the Perl debugger and pull in Devel::DProf who will then install it's hooks into the debugger and start it's profile timer. The END subroutine installed by Devel::DProf will be run when the child server is shutdown and the $ServerRoot/dprof/$$/tmon.out file will be generated and ready for dprofpp.

NOTE: $ServerRoot/logs/dprof/ will need to be writable by the user Apache is running as (i.e. nobody, apache, etc.). If you can not write to $ServerRoot as this user, set $ENV{APACHE_DPROF_PATH_ABSOLUTE} to an absolute path of a directory this user can.

Originally written by Doug MacEachern

Currently maintained by Frank Wiles <frank@wiles.org>

This module is distributed under the same terms as Perl itself.

Devel::DProf(3), Apache::DB(3), mod_perl(3), Apache(3)