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).

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