Is mod_authnz_external thread-safe?

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This is how I set up a "stress test" for Apache:

1. Set up a web page that issues 100 AJAX requests within a short period of time
2. Using the about:config page in Firefox, modify the parameter 
network.http.max-persistent-connections-per-server to allow 50 simultaneous 
connections 
3. Set up Apache so that the MPM operates in worker mode (rather than prefork).

What is the expected output? What do you see instead?

When I run the stress test, about 10% of the AJAX requests are lost, and the
Apache error logs contain entries like this:

[cgid:error] [pid 27442:tid 1] AH01239: cgid daemon process died, restarting

There are several ways I can make the problem go away: (1) change the MPM
to use prefork rather than worker, (2) change the authentication mode to use
file authentication instead of external authentication, (3) decrease the 
number of simultaneous connections used by Firefox.  However it appears that
mod_authnz_external is unable work properly under heavy loads when threading
is used.

What version of the product are you using? On what operating system?

I am running Apache 2.4.10 with version 3.2.3 of mod_authnz_external

Please provide any additional information below.

I did my testing on an HP Integrity box running HP-UX 11.31.  

If mod_authnz_external simply does not support thread safety, then I will set 
up my Apache server to use prefork, but I would like to use threading if
possible.

Original issue reported on code.google.com by jim90...@gmail.com on 4 Feb 2015 at 8:06