In devoloping CGI scripts, I noticed that my apache server set stack size as 10MB for apache users. However, my cgi script needs to invoke a C executable that requires a larger stack size. I wonder how to increase the stack size for apache users.

I tried the following 2 approaches:
(1) to modify the /etc/security/limits.conf" file to increase all users' stack size by adding
"* soft stack unlimited"
and
"* hard stack unlimited".

(2) to modify the httpd.conf by adding "ThreadStackSize 65536*1024" (64MB should be big enough).

However, apache users still had 10MB stack size (this information was obtained via "ulimit -a") after two modifications.

BTW, I am using redhat enterprise linux in my server.

I believe that the "ThreadStackSize" directive can be used to increase the stack size for "apache" users. However, in order to make this directive effective, the "worker" MPM has to be used. Since only one core MPM can be activated at a time, how should I change my MPM from "prefork" (the default MPM in my server) to "worker"?

That's what I have done:
I made the binary of "/etc/sysconfig/httpd" point to "/usr/sbin/httpd.worker". Then, I restarted the httpd service ("service httpd restart") but got the following error information:
------------------------------------------------------------------------
[root@poplar sysconfig]# service httpd restart
Stopping httpd: [FAILED]
Starting httpd: [Wed Oct 25 12:39:22 2006] [crit] Apache is running a
threaded MPM, but your PHP Module is not compiled to be threadsafe. You
need to recompile PHP.
Pre-configuration failed [FAILED]
-------------------------------------------------------------------------
It seems that this thread-based model, 'worker', does not work with PHP modules.

What should I do then?