EventMachine: fast, simple event-processing library for Ruby programs
Ruby C++ Java C
Pull request Compare This branch is 1 commit ahead, 455 commits behind eventmachine:master.
Latest commit 053cdc4 Nov 13, 2011 @gdb Add a basic dynamic environments implementation
If an exception is raised in the middle of a callback (and not handled
in the callback), the only opportunity the programmer has to deal with
it is in the global error handler. However, in the error handler, the
context in which the error was raised has been lost. With this patch,
callbacks can store values in dynamic environments. If an exception is
raised, the global error handler can access the same dynamic


'EventMachine::Environment.dynamic_env' returns the current dynamic
env, which can be accessed like a hash.


require 'rubygems'
require 'eventmachine'

EventMachine.error_handler do |er|
  puts "Foo key is #{EventMachine::Environment.dynamic_env[:foo].inspect}"

EventMachine.next_tick do
  EventMachine::Environment.dynamic_env[:foo] = :bar
  raise 'Raised!'



- This hasn't been tested extensively. I'm sure it doesn't work in
  corner cases. I wouldn't be shocked if it doesn't work in most
  normal cases.

- The code is pretty bad right now. I'll fix it up later once it's
  closer to a final version.


About EventMachine

What is EventMachine

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.

What EventMachine is good for?

What platforms are supported by EventMachine?

EventMachine supports Ruby 1.8.7, 1.9.2, REE, JRuby and works well on Windows as well as many operating systems from the Unix family (Linux, Mac OS X, BSD flavors).

Install the gem

Install it with RubyGems

gem install eventmachine

or add this to your Gemfile if you use Bundler:

gem "eventmachine"

Getting started

For an introduction to EventMachine, check out:

Server example: Echo server

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

 require 'eventmachine'

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

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

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

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

EventMachine documentation

Currently we only have reference documentation and a wiki.

Community and where to get help

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

License and copyright

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 Cool.io. One caveat: by May 2011, it did not support JRuby and Windows.