+ (** Daemon behaviour wrt request handling. `Single mode use a single process
+ to handle all requests, no request is served until a previous one has been
+ fully served. `Fork mode fork a new process for each request, the new process
+ will execute the callback function and then exit. `Thread mode create a new
+ thread for each request, the new thread will execute the callback function and
+ then exit, threads can communicate using standard OCaml Thread library. *)