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From Ali Shah <caff...@gmail.com>
Subject apr_global_mutex_create vs apr_proc_mutex_create
Date Wed, 23 Mar 2016 20:49:19 GMT
Hi Module maintainers,

I'm writing a simple apache module and I'd like to aggregate some
statistics.
I saw an example module that does this (
https://wiki.apache.org/httpd/ModuleLife) using shared memory.

My question for those on this list following:

What is the main difference between using mutexes created
via apr_global_mutex_create and apr_proc_mutex_create in terms of
performance and safety of the resource that being protected?

The docs seem to discourage usage of apr_global_mutex_create:
"There is considerable overhead in using this API if only cross-process or
cross-thread mutual exclusion is required."

Is the overhead purely in code setup (since global mutex should be
initialized in post_config), or is this describing some performance
penalties as well?

Thanks!
Ali

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