modify request_rec->args

Hello, I have a simple module, with just a quick_hander, it's sole function is to check if there is a specific key=value on the query string, and modify the value, so it gets picked up by a separate module. For example: if "foo=1" is in r->args, then replace it with "foo=0", decline the request

Re: apr_global_mutex_create vs apr_proc_mutex_create

proc_mutex can only be used to block on a cross process event. It can be used in a threaded server, but cannot be held in multiple threads, you might use it to block in a single thread queue per-process. Thread_mutex will not block between processes, this is used for the mutex-per-process logic