I'm not the biggest expert in the world on this, but since no one else answered you, :-) here is the basic problem, as demonstrated in this old newsgroup posting.

#!/usr/bin/perl
use warnings;
use strict;

#Benjamin Goldberg 
#The Apache process does NOT wait for the CGI 
#process to exit, it waits 
#for the pipes to be closed. 
# (Note that if the CGI is a NPH script, then 
#it does waitpid() for the script to exit). 
#Thus, you do not really need a child process 
#-- you can have your CGI 
#process transmute itself into whatever you 
#would have the child process 
#do, by doing something like: 

$| = 1;     # need either this or to explicitly flush stdout, etc. 
print "Content-type: text/plain\n\n";
print "Going to start the fork now\n";
open( STDIN, "</dev/null");
open( STDOUT, ">>/dev/null");
open( STDERR, ">>/path/to/logfile");
fork and exit;
exec "program that would be the child process";

#Apache waits for all children to close the pipes to apache.  It 
#does not wait for them to actually exit -- think ... 
#how in the world could it *possibly* know that those 
#processes were really spawned from 
#the CGI process?  Answer:  It can't.  It can only know 
#that *something* still has an open filedescriptor which 
#points to one of the pipes that 
#apache created to capture the CGI's stdout and stderr.  
#As long as one of these pipes is open, then apache waits.
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