+httpd-dev@ Hello!
2016-03-23 21:49 GMT+01:00 Ali Shah <caff...@gmail.com>: > 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? > >From what I can see in [1] a global lock uses both apr_proc_mutex_create and apr_thread_mutex_create, so this is why the documentation suggests the use of a more specialized one if only cross-process or cross-thread sync is needed. Not a great explanation I know, somebody else with more experience will give you a better answer on this list :) Luca [1]: https://github.com/apache/apr/blob/7951861fb029fd0fb60e5ec8da73015d03afa28d/locks/unix/global_mutex.c#L46
