# ![nio4r](https://raw.github.com/socketry/nio4r/master/logo.png)

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_NOTE: This is the 2.x **stable** branch of nio4r.  For the 1.x **legacy** branch,
please see:_

https://github.com/socketry/nio4r/tree/1-x-stable

**New I/O for Ruby (nio4r)**: cross-platform asynchronous I/O primitives for
scalable network clients and servers. Modeled after the Java NIO API, but
simplified for ease-of-use.

**nio4r** provides an abstract, cross-platform stateful I/O selector API for Ruby.
I/O selectors are the heart of "reactor"-based event loops, and monitor
multiple I/O objects for various types of readiness, e.g. ready for reading or
writing.

## Projects using nio4r

* [ActionCable]: Rails 5 WebSocket protocol, uses nio4r for a WebSocket server
* [Celluloid::IO]: Actor-based concurrency framework, uses nio4r for async I/O
* [Socketry Async]: Asynchronous I/O framework for Ruby

[ActionCable]: https://rubygems.org/gems/actioncable
[Celluloid::IO]: https://github.com/celluloid/celluloid-io
[Socketry Async]: https://github.com/socketry/async

## Goals

* Expose high-level interfaces for stateful IO selectors
* Keep the API small to maximize both portability and performance across many
  different OSes and Ruby VMs
* Provide inherently thread-safe facilities for working with IO objects

## Supported platforms

* Ruby 2.3
* Ruby 2.4
* Ruby 2.5
* Ruby 2.6
* JRuby 9000

## Supported backends

* **libev**: MRI C extension targeting multiple native IO selector APIs (e.g epoll, kqueue)
* **Java NIO**: JRuby extension which wraps the Java NIO subsystem
* **Pure Ruby**: `Kernel.select`-based backend that should work on any Ruby interpreter

## Discussion

For discussion and general help with nio4r, email
[socketry+subscribe@googlegroups.com][subscribe]
or join on the web via the [Google Group].

We're also on IRC at ##socketry on irc.freenode.net.

[subscribe]:    mailto:socketry+subscribe@googlegroups.com
[google group]: https://groups.google.com/group/socketry

## Documentation

[Please see the nio4r wiki](https://github.com/socketry/nio4r/wiki)
for more detailed documentation and usage notes:

* [Getting Started]: Introduction to nio4r's components
* [Selectors]: monitor multiple `IO` objects for readiness events
* [Monitors]: control interests and inspect readiness for specific `IO` objects
* [Byte Buffers]: fixed-size native buffers for high-performance I/O

[Getting Started]: https://github.com/socketry/nio4r/wiki/Getting-Started
[Selectors]: https://github.com/socketry/nio4r/wiki/Selectors
[Monitors]: https://github.com/socketry/nio4r/wiki/Monitors
[Byte Buffers]: https://github.com/socketry/nio4r/wiki/Byte-Buffers

See also:

* [YARD API documentation](http://www.rubydoc.info/gems/nio4r/frames)

## Non-goals

**nio4r** is not a full-featured event framework like [EventMachine] or [Cool.io].
Instead, nio4r is the sort of thing you might write a library like that on
top of. nio4r provides a minimal API such that individual Ruby implementers
may choose to produce optimized versions for their platform, without having
to maintain a large codebase.

[EventMachine]: https://github.com/eventmachine/eventmachine
[Cool.io]: https://coolio.github.io/

## License

Copyright (c) 2011-2018 Tony Arcieri. Distributed under the MIT License.
See [LICENSE.txt] for further details.

Includes libev 4.24. Copyright (c) 2007-2016 Marc Alexander Lehmann.
Distributed under the BSD license. See [ext/libev/LICENSE] for details.

[LICENSE.txt]: https://github.com/socketry/nio4r/blob/master/LICENSE.txt
[ext/libev/LICENSE]: https://github.com/socketry/nio4r/blob/master/ext/libev/LICENSE
