libuv

Cross-platform asynchronous I/O

libuv
24347
3605
C

libuv

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, Julia,
uvloop, and others.

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
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.

Licensing

libuv is licensed under the MIT license. Check the LICENSE and
LICENSE-extra files.

The documentation is licensed under the CC BY 4.0 license. Check the
LICENSE-docs file.

Community

Documentation

Official documentation

Located in the docs/ subdirectory. It uses the Sphinx
framework, which makes it possible to build the documentation in multiple
formats.

Show different supported building options:

$ make help

Build documentation as HTML:

$ 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):

$ make livehtml

Build documentation as man pages:

$ make man

Build documentation as ePub:

$ make epub

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

Documentation can be browsed online here.

The tests and benchmarks
also serve as API specification and usage examples.

Other resources

  • LXJS 2012 talk
    — High-level introductory talk about libuv.
  • libuv-dox
    — Documenting types and methods of libuv, mostly by reading uv.h.
  • 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These resources are not handled by libuv maintainers and might be out of
date.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
or from the downloads site.

Before verifying the git tags or signature files, importing the relevant keys
is necessary. Key IDs are listed in the
MAINTAINERS
file, but are also available as git blob objects for easier use.

Importing a key the usual way:

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

Importing a key from a git blob object:

$ git show pubkey-saghul | gpg --import

Verifying releases

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

$ git verify-tag v1.6.1

Starting with libuv 1.7.0, the tarballs stored in the
downloads site 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:

$ 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:

  • 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.

To build with autotools:

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

To build with CMake:

$ 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):

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

Install with Homebrew

$ 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”).

Install with vcpkg

$ git clone https://github.com/microsoft/vcpkg.git
$ ./bootstrap-vcpkg.bat # for powershell
$ ./bootstrap-vcpkg.sh # for bash
$ ./vcpkg install libuv

Install with Conan

You can install pre-built binaries for libuv or build it from source using Conan. Use the following command:

conan install --requires="libuv/[*]" --build=missing

The libuv Conan recipe is kept up to date by Conan maintainers and community contributors.
If the version is out of date, please create an issue or pull request on the ConanCenterIndex repository.

Running tests

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

$ 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:

$ build/uv_run_tests_a TEST_NAME

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

$ 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 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:

$ 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.

-fno-strict-aliasing

It is recommended to turn on the -fno-strict-aliasing compiler flag in
projects that use libuv. The use of ad hoc “inheritance” in the libuv API
may not be safe in the presence of compiler optimizations that depend on
strict aliasing.

MSVC does not have an equivalent flag but it also does not appear to need it
at the time of writing (December 2019.)

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
describes the package in more detail.

z/OS Notes

z/OS compilation requires ZOSLIB to be installed. When building with CMake, use the flag -DZOSLIB_DIR to specify the path to ZOSLIB:

$ (cd build && cmake .. -DBUILD_TESTING=ON -DZOSLIB_DIR=/path/to/zoslib)
$ cmake --build build

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.