The libevent api provides a mechanism to execute a callback function when a specific event occurs on a file descriptor or after a timeout has been reached.

libevent is meant to replace the asynchronous event loop found in event driven network servers. currently, libevent supports /dev/poll, kqueue(2), event ports, select(2), poll(2) and epoll(4).

the libevent_extra library includes code for http, dns, rpc, and so on.

if you're writing software that uses libevent's protocol support, you need to link libevent_core and libevent_extra as well.