in reply to running mod_perl code before the fork

There is the post-config phase (PerlPostConfigHandler) but I thought mod_perl could use that only as from Apache 2.

The post-config phase is special as it is likely to run twice.

From the docs:

PerlPostConfigHandler

The post_config phase happens right after Apache has processed the configuration files, before any child processes were spawned (which happens at the child_init phase).

This phase can be used for initializing things to be shared between all child processes. You can do the same in the startup file, but in the post_config phase you have an access to a complete configuration tree

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James