I'd do it differently. Try this:

#!/usr/bin/perl -l

use strict;
use warnings;
use ModPerl::Util;
use ModPerl::Const -compile => 'EXIT';

register_user();
my $pid = fork();
if( $pid == 0 ){
  send_mail();
  eval {
      exit;
  };
  exit if $@ && ref $@ eq 'APR::Error' && $@ == ModPerl::EXIT;
  print "Still running";
}
write_log();

sub register_user {
    print "Registering user."
}

sub send_mail { print "Mail sent..."; };
sub write_log { print "Written to log..."; };
[download]