C Socket Programming

currently writing a client and a server program who exchange data via UDPv6/IPv6 and using ARQ with sequencenumbers and ACKs to ensure the data was send correctly
to do this you have to change the socket to O_NONBLOCK and then theres comes this tricky select()/pselect() function and I really cant get it to work
does some of you got an example for this problem?

select() is shit, use poll().