EventMachine is an event-driven I/O and lightweight concurrency library for Ruby. It provides event-driven I/O using the Reactor pattern, much like JBoss Netty, Apache MINA, Python's Twisted, Node.js, libevent and libev.

EventMachine is designed to simultaneously meet two key needs:

• Extremely high scalability, performance and stability for the most demanding production environments.
• An API that eliminates the complexities of high-performance threaded network programming, allowing engineers to concentrate on their application logic.

This unique combination makes EventMachine a premier choice for designers of critical networked applications, including Web servers and proxies, email and IM production systems, authentication/authorization processors, and many more.

EventMachine has been around since the early 2000s and is a mature and battle-tested library.

• Scalable event-driven servers. Examples: Thin or Goliath.
• Scalable asynchronous clients for various protocols, RESTful APIs and so on. Examples: em-http-request or amqp gem.
• Efficient network proxies with custom logic. Examples: Proxymachine.
• File and network monitoring tools. Examples: eventmachine-tail and logstash.

EventMachine supports Ruby 2.0.0 and later (see tested versions at .github/workflows/workflow.yml). It runs on JRuby and works well on Windows as well as many operating systems from the Unix family (Linux, Mac OS X, BSD flavors).

Install it with RubyGems

gem install eventmachine

or add this to your Gemfile if you use Bundler:

gem 'eventmachine'

For an introduction to EventMachine, check out:

• blog post about EventMachine by Ilya Grigorik.
• EventMachine Introductions by Dan Sinclair.

Here's a fully-functional echo server written with EventMachine:

 require 'eventmachine'

 module EchoServer
   def post_init
     puts "-- someone connected to the echo server!"
   end

   def receive_data data
     send_data ">>>you sent: #{data}"
     close_connection if data =~ /quit/i
   end

   def unbind
     puts "-- someone disconnected from the echo server!"
   end
end

# Note that this will block current thread.
EventMachine.run {
  EventMachine.start_server "127.0.0.1", 8081, EchoServer
}

Currently we only have reference documentation and a wiki.

• Join the mailing list (Google Group)
• Join IRC channel #eventmachine on irc.freenode.net

EventMachine is copyrighted free software made available under the terms of either the GPL or Ruby's License.

Copyright: (C) 2006-07 by Francis Cianfrocca. All Rights Reserved.

If you are unhappy with EventMachine and want to use Ruby, check out Celluloid.