This ‘book’ is a small set of tutorials about using libuv as a high performance evented I/O library which offers the same API on Windows and Unix.

It is meant to cover the main areas of libuv, but is not a comprehensive reference discussing every function and data structure. The official libuv documentation may be consulted for full details.

This book is still a work in progress, so sections may be incomplete, but I hope you will enjoy it as it grows.

Who this book is for#

If you are reading this book, you are either:

  1. a systems programmer, creating low-level programs such as daemons or network services and clients. You have found that the event loop approach is well suited for your application and decided to use libuv.

  2. a node.js module writer, who wants to wrap platform APIs written in C or C++ with a set of (a)synchronous APIs that are exposed to JavaScript. You will use libuv purely in the context of node.js. For this you will require some other resources as the book does not cover parts specific to v8/node.js.

This book assumes that you are comfortable with the C programming language.


The node.js project began in 2009 as a JavaScript environment decoupled from the browser. Using Google’s V8 and Marc Lehmann’s libev, node.js combined a model of I/O – evented – with a language that was well suited to the style of programming; due to the way it had been shaped by browsers. As node.js grew in popularity, it was important to make it work on Windows, but libev ran only on Unix. The Windows equivalent of kernel event notification mechanisms like kqueue or (e)poll is IOCP. libuv was an abstraction around libev or IOCP depending on the platform, providing users an API based on libev. In the node-v0.9.0 version of libuv libev was removed.

Since then libuv has continued to mature and become a high quality standalone library for system programming. Users outside of node.js include Mozilla’s Rust programming language, and a variety of language bindings.

This book and the code is based on libuv version v1.42.0.


All the example code and the source of the book is included as part of the libuv project on GitHub. Clone or Download libuv, then build it:


There is no need to make install. To build the examples run make in the docs/code/ directory.