![libuv][libuv_banner]

## Overview

libuv is a multi-platform support library with a focus on asynchronous I/O. It
was primarily developed for use by [Node.js][], but it's also
used by [Luvit](http://luvit.io/), [Julia](http://julialang.org/),
[pyuv](https://github.com/saghul/pyuv), and [others](https://github.com/libuv/libuv/wiki/Projects-that-use-libuv).

## Feature highlights

 * Full-featured event loop backed by epoll, kqueue, IOCP, event ports.

 * Asynchronous TCP and UDP sockets

 * Asynchronous DNS resolution

 * Asynchronous file and file system operations

 * File system events

 * ANSI escape code controlled TTY

 * IPC with socket sharing, using Unix domain sockets or named pipes (Windows)

 * Child processes

 * Thread pool

 * Signal handling

 * High resolution clock

 * Threading and synchronization primitives

## Versioning

Starting with version 1.0.0 libuv follows the [semantic versioning](http://semver.org/)
scheme. The API change and backwards compatibility rules are those indicated by
SemVer. libuv will keep a stable ABI across major releases.

The ABI/API changes can be tracked [here](http://abi-laboratory.pro/tracker/timeline/libuv/).

## Licensing

libuv is licensed under the MIT license. Check the [LICENSE file](LICENSE).
The documentation is licensed under the CC BY 4.0 license. Check the [LICENSE-docs file](LICENSE-docs).

## Community

 * [Support](https://github.com/libuv/help)
 * [Mailing list](http://groups.google.com/group/libuv)
 * [IRC chatroom (#libuv@irc.freenode.org)](http://webchat.freenode.net?channels=libuv&uio=d4)

## Documentation

### Official documentation

Located in the docs/ subdirectory. It uses the [Sphinx](http://sphinx-doc.org/)
framework, which makes it possible to build the documentation in multiple
formats.

Show different supported building options:

```bash
$ make help
```

Build documentation as HTML:

```bash
$ make html
```

Build documentation as HTML and live reload it when it changes (this requires
sphinx-autobuild to be installed and is only supported on Unix):

```bash
$ make livehtml
```

Build documentation as man pages:

```bash
$ make man
```

Build documentation as ePub:

```bash
$ make epub
```

NOTE: Windows users need to use make.bat instead of plain 'make'.

Documentation can be browsed online [here](http://docs.libuv.org).

The [tests and benchmarks](https://github.com/libuv/libuv/tree/master/test)
also serve as API specification and usage examples.

### Other resources

 * [LXJS 2012 talk](http://www.youtube.com/watch?v=nGn60vDSxQ4)
   — High-level introductory talk about libuv.
 * [libuv-dox](https://github.com/thlorenz/libuv-dox)
   — Documenting types and methods of libuv, mostly by reading uv.h.
 * [learnuv](https://github.com/thlorenz/learnuv)
   — Learn uv for fun and profit, a self guided workshop to libuv.

These resources are not handled by libuv maintainers and might be out of
date. Please verify it before opening new issues.

## Downloading

libuv can be downloaded either from the
[GitHub repository](https://github.com/libuv/libuv)
or from the [downloads site](http://dist.libuv.org/dist/).

Before verifying the git tags or signature files, importing the relevant keys
is necessary. Key IDs are listed in the
[MAINTAINERS](https://github.com/libuv/libuv/blob/master/MAINTAINERS.md)
file, but are also available as git blob objects for easier use.

Importing a key the usual way:

```bash
$ gpg --keyserver pool.sks-keyservers.net --recv-keys AE9BC059
```

Importing a key from a git blob object:

```bash
$ git show pubkey-saghul | gpg --import
```

### Verifying releases

Git tags are signed with the developer's key, they can be verified as follows:

```bash
$ git verify-tag v1.6.1
```

Starting with libuv 1.7.0, the tarballs stored in the
[downloads site](http://dist.libuv.org/dist/) are signed and an accompanying
signature file sit alongside each. Once both the release tarball and the
signature file are downloaded, the file can be verified as follows:

```bash
$ gpg --verify libuv-1.7.0.tar.gz.sign
```

## Build Instructions

For UNIX-like platforms, including macOS, there are two build methods:
autotools or [CMake][].

For Windows, [CMake][] is the only supported build method and has the
following prerequisites:

<details>

* One of:
  * [Visual C++ Build Tools][]
  * [Visual Studio 2015 Update 3][], all editions
    including the Community edition (remember to select
    "Common Tools for Visual C++ 2015" feature during installation).
  * [Visual Studio 2017][], any edition (including the Build Tools SKU).
    **Required Components:** "MSbuild", "VC++ 2017 v141 toolset" and one of the
    Windows SDKs (10 or 8.1).
* Basic Unix tools required for some tests,
  [Git for Windows][] includes Git Bash
  and tools which can be included in the global `PATH`.

</details>

To build with autotools:

```bash
$ sh autogen.sh
$ ./configure
$ make
$ make check
$ make install
```

To build with [CMake][]:

```bash
$ mkdir -p build

$ (cd build && cmake .. -DBUILD_TESTING=ON) # generate project with tests
$ cmake --build build                       # add `-j <n>` with cmake >= 3.12

# Run tests:
$ (cd build && ctest -C Debug --output-on-failure)

# Or manually run tests:
$ build/uv_run_tests                        # shared library build
$ build/uv_run_tests_a                      # static library build
```

To cross-compile with [CMake][] (unsupported but generally works):

```bash
$ cmake ../..                 \
  -DCMAKE_SYSTEM_NAME=Windows \
  -DCMAKE_SYSTEM_VERSION=6.1  \
  -DCMAKE_C_COMPILER=i686-w64-mingw32-gcc
```

### Install with Homebrew

```bash
$ brew install --HEAD libuv
```

Note to OS X users:

Make sure that you specify the architecture you wish to build for in the
"ARCHS" flag. You can specify more than one by delimiting with a space
(e.g. "x86_64 i386").

### Running tests

Some tests are timing sensitive. Relaxing test timeouts may be necessary
on slow or overloaded machines:

```bash
$ env UV_TEST_TIMEOUT_MULTIPLIER=2 build/uv_run_tests # 10s instead of 5s
```

#### Run one test

The list of all tests is in `test/test-list.h`.

This invocation will cause the test driver to fork and execute `TEST_NAME` in
a child process:

```bash
$ build/uv_run_tests_a TEST_NAME
```

This invocation will cause the test driver to execute the test in
the same process:

```bash
$ build/uv_run_tests_a TEST_NAME TEST_NAME
```

#### Debugging tools

When running the test from within the test driver process
(`build/uv_run_tests_a TEST_NAME TEST_NAME`), tools like gdb and valgrind
work normally.

When running the test from a child of the test driver process
(`build/uv_run_tests_a TEST_NAME`), use these tools in a fork-aware manner.

##### Fork-aware gdb

Use the [follow-fork-mode](https://sourceware.org/gdb/onlinedocs/gdb/Forks.html) setting:

```
$ gdb --args build/uv_run_tests_a TEST_NAME

(gdb) set follow-fork-mode child
...
```

##### Fork-aware valgrind

Use the `--trace-children=yes` parameter:

```bash
$ valgrind --trace-children=yes -v --tool=memcheck --leak-check=full --track-origins=yes --leak-resolution=high --show-reachable=yes --log-file=memcheck-%p.log build/uv_run_tests_a TEST_NAME
```

### Running benchmarks

See the section on running tests.
The benchmark driver is `./uv_run_benchmarks_a` and the benchmarks are
listed in `test/benchmark-list.h`.

## Supported Platforms

Check the [SUPPORTED_PLATFORMS file](SUPPORTED_PLATFORMS.md).

### AIX Notes

AIX compilation using IBM XL C/C++ requires version 12.1 or greater.

AIX support for filesystem events requires the non-default IBM `bos.ahafs`
package to be installed.  This package provides the AIX Event Infrastructure
that is detected by `autoconf`.
[IBM documentation](http://www.ibm.com/developerworks/aix/library/au-aix_event_infrastructure/)
describes the package in more detail.

### z/OS Notes

z/OS creates System V semaphores and message queues. These persist on the system
after the process terminates unless the event loop is closed.

Use the `ipcrm` command to manually clear up System V resources.

## Patches

See the [guidelines for contributing][].

[CMake]: https://cmake.org/
[node.js]: http://nodejs.org/
[guidelines for contributing]: https://github.com/libuv/libuv/blob/master/CONTRIBUTING.md
[libuv_banner]: https://raw.githubusercontent.com/libuv/libuv/master/img/banner.png
[Visual C++ Build Tools]: https://visualstudio.microsoft.com/visual-cpp-build-tools/
[Visual Studio 2015 Update 3]: https://www.visualstudio.com/vs/older-downloads/
[Visual Studio 2017]: https://www.visualstudio.com/downloads/
[Git for Windows]: http://git-scm.com/download/win