On 2013-06-11 21:20, Alex Bligh wrote:
I've written a module which I believe to be thread-safe but appears to be
doing something which I have put down to a lack of thread safety in pool
management (somewhere).
Before I tear my hair out here, my module is running with apache 2.2.22
and mpm-prefork on Ubuntu. Do the thread primatives actually do anything in
mpm-prefork? I'm using apr_thread_create to create a thread, then
providing a separate allocator, mutex, pool and similar (all as
recommended). But if the mutex stuff is 'optimised out' of my apr
library - specifically the pool stuff - all this will be in vain.
apr_* and mpm_prefork are different software packages and ubuntu
distributes them separately. So it is almost certain that you have a
thread-enabled libapr (i.e. compiled with APR_HAS_THREADS). You would
not be able to compile the code that uses apr_thread_create if your
libapr was not compiled with thread support.
mpm_prefork is like any ordinary client of libapr. Just that it does not
use the threading functionality in libapr. So it cannot disable/optimise
out the mutexes in libapr.
Please be aware that apr_pools are not thread-safe. Only the creation of
subpools is thread-safe. So you should create a subpool per thread to
stay safe.
Sorin
