Libevent is an asynchronous event notification library that provides a mechanism to execute a callback function when a specific event occurs on a file descriptor or after a timeout has been reached.

it 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).

for backward compatibility and to transition to "libevent_core only" or "libevent_core + libevent_extra", the libevent source package builds the libevent library that includes everything in libevent_core and libevent_extra.