as TS_RESP_CTX is not thread safe, this commit implement a pool of
TS_RESP_CTX in which a thread can pick one in a thread safe maner.
* implement a ts_resp_ctx_wrapper containing a TS_RESP_CTX and a
lock and bool to mark the availability of the TS_RESP_CTX
* implement the get_ctxw to recover a given TS_RESP_CTX in a thread safe
maner
* adapt the rest of the code to accomodate the new way of doing things
* set the default number of threads to 10 as it's now safe to do so
* add a pid file option on command line + implement it
* make the relative path in conf param relative to the configuration
file directory and not the running directory
as many configuration paths can be relative to the execution working
directory, this directory is recorded at launch time, and the set_params
function does a chdir(<start work dir>); <load conf>; chdir("/") when
it's called.
* split the rfc3161 and the http part
* add a logger function
* add a debugging logger function for the requests
* add a specific handler for rfc3161 request
