Dealing with Variables
The configuration structures should normally be treated as read-only
outside of the functions discussed above. A few limited exceptions
may be appropriate, usually on the server config, where it is used to
manage, for example, a pool or cache of resources whose contents
might change at any time. This can safely be done in a
post_config or child_init hook. But at any
later point - when processing a Connection or Request - this gives rise
to a race condition. Any such operations must therefore use an
appropriate lock: usually an apr_thread_mutex (which must
itself be set up during module initialisation).
