An asynchronous event notification library (extra) 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.