I am trying to get some more info and documentation on APR threads and APR pools. I find the documentation pretty scarce so far.
For APR pools, the link "Using APR Pools" (http://svn.apache.org/viewcvs.cgi/apr/apr/docs/pool-design.html ) on the APR apache web site is unfortunately not working.
Anyhow, I've been grepping the Apache source code to find out how to use the APR pool and APR threads API.

In the prototype I am working on, I have multi-threaded processes sharing a shared-memory buffer (setup through a system call similar to MMAP shared). I have to synchronize accesses to shared data found in the shared buffer. I can actually do this using pthreads and I was the first one to be surprised. Your pthread mutex can reside on the shared memory buffer, one process can call ptrhead_mutex_init() and the other process can start using and locking on that mutex.

Now APR pools greatly complicate my situation. If I undestand correctly, apr_thread_mutex_create() needs a pool and the actual mutex will be allocated from that pool. The location of that pool in memory will not be shared among my processes. So is that a limitation of APR mutexes ? APR mutexes cannot be shared among processes ? Is there a way to get around that ? Is there a hack that could be done by using a special memory allocator for that pool ?

I am sure that the answer is that I am using the APR library for something that it was not designed for. Unfortunately, it is hard to get a feel of how to use a library correctly when documentation about the library is scarce.

So maybe I should give some background on what I am working on. I am working with Apache, mod_ssl and openssl. Apache is running with the worker MPM.
I have modified Apache so that the apache processes share a shared-memory buffer (basically setup through a syscall similar to mmap shared). I have a special SSL engine that takes care of cerficate signatures. Each apache thread servicing an SSL connection queues the signature request in the shared buffer which is processed by an outside application responsible for encryption. So I need a way to synchronize the various threads inside each apache process.