The Libevent Reference Manual: Preliminaries

A program written using Libevent should work across all the platforms Libevent supports. Even when there is no really good way to do nonblocking IO, Libevent should support the so-so ways, so that your program can run in restricted environments.

Libevent tries to use the fastest available nonblocking IO implementations on each platform, and not to introduce much overhead as it does so.

Libevent is designed to work well even with programs that need to have tens of thousands of active sockets.

Whenever possible, the most natural way to write a program with Libevent should be the stable, portable way.

Generic functionality to abstract out the differences between different platforms' networking implementations.

This is the heart of Libevent. It provides an abstract API to the various platform-specific, event-based nonblocking IO backends. It can let you know when sockets are ready to read or write, do basic timeout functionality, and detect OS signals.

These functions provide a more convenient wrapper around Libevent’s event-based core. They let your application request buffered reads and writes, and rather than informing you when sockets are ready to do, they let you know when IO has actually occurred.

The bufferevent interface also has multiple backends, so that
it can take advantage of systems that provide faster ways to do
nonblocking IO, such as the Windows IOCP API.

This module implements the buffers underlying bufferevents, and provides functions for efficient and/or convenient access.

A simple HTTP client/server implementation.

A simple DNS client/server implementation.

A simple RPC implementation.

All core event and buffer functionality. This library contains all the event_base, evbuffer, bufferevent, and utility functions.

This library defines protocol-specific functionality that you may or may not want for your application, including HTTP, DNS, and RPC.

This library exists for historical reasons; it contains the contents of both libevent_core and libevent_extra. You shouldn’t use it; it may go away in a future version of Libevent.

This library adds threading and locking implementations based on the pthreads portable threading library. It is separated from libevent_core so that you don’t need to link against pthreads to use Libevent unless you are actually using Libevent in a multithreaded way.

This library provides support for encrypted communications using bufferevents and the OpenSSL library. It is separated from libevent_core so that you don’t need to link against OpenSSL to use Libevent unless you are actually using encrypted connections.

An API header is one that defines current public interfaces to Libevent. These headers have no special suffix.

A compatibility header includes definitions for deprecated functions. You shouldn’t include it unless you’re porting a program from an older version of Libevent.

These headers define structures with relatively volatile layouts. Some of these are exposed in case you need fast access to structure component; some are exposed for historical reasons. Relying on any of the structures in headers directly can break your program’s binary compatibility with other versions of Libevent, sometimes in hard-to-debug ways. These headers have the suffix "_struct.h"