Internal Program Version: libevent-1.4 1.4.13

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).

http://www.monkey.org/~provos/libevent/