Concurrent Ruby

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Modern concurrency tools for Ruby. Inspired by Erlang, Clojure, Scala, Haskell, F#, C#, Java, and classic concurrency patterns.

The design goals of this gem are:

  • Be an 'unopinionted' toolbox that provides useful utilities without debating which is better or why
  • Remain free of external gem dependencies
  • Stay true to the spirit of the languages providing inspiration
  • But implement in a way that makes sense for Ruby
  • Keep the semantics as idiomatic Ruby as possible
  • Support features that make sense in Ruby
  • Exclude features that don't make sense in Ruby
  • Be small, lean, and loosely coupled


gem install concurrent-ruby

or add the following line to Gemfile:

gem 'concurrent-ruby'

and run bundle install from your shell.

NOTE: There is an old gem from 2007 called "concurrent" that does not appear to be under active development. That isn't us. Please do not run* gem install concurrent*. It is not the droid you are looking for.

Features & Documentation

Please see the Concurrent Ruby Wiki or the API documentation for more information or join our mailing list.

There are many concurrency abstractions in this library. These abstractions can be broadly categorized into several general groups:

Semantic Versioning

This gem adheres to the rules of semantic versioning.

Supported Ruby versions

MRI 1.9.3, 2.0, 2.1, JRuby (1.9 mode), and Rubinius 2.x. This library is pure Ruby and has no gem dependencies. It should be fully compatible with any interpreter that is compliant with Ruby 1.9.3 or newer.


Many more code examples can be found in the documentation for each class (linked above). This one simple example shows some of the power of this gem.

require 'concurrent'
require 'thread'   # for Queue
require 'open-uri' # for open(uri)

class Ticker
  def get_year_end_closing(symbol, year)
    uri = "{symbol}&a=11&b=01&c=#{year}&d=11&e=31&f=#{year}&g=m"
    data = open(uri) {|f| f.collect{|line| line.strip } }

# Future
price = Concurrent::Future.execute{'TWTR', 2013) }
price.state #=> :pending
sleep(1)    # do other stuff
price.value #=> 63.65
price.state #=> :fulfilled

# Promise
prices ={ puts'AAPL', 2013) }.
           then{ puts'MSFT', 2013) }.
           then{ puts'GOOG', 2013) }.
           then{ puts'AMZN', 2013) }.execute
prices.state #=> :pending
sleep(1)     # do other stuff
#=> 561.02
#=> 37.41
#=> 1120.71
#=> 398.79

# ScheduledTask
task = Concurrent::ScheduledTask.execute(2){'INTC', 2013) }
task.state #=> :pending
sleep(3)   # do other stuff
task.value #=> 25.96



  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request

License and Copyright

Concurrent Ruby is free software released under the MIT License.

The Concurrent Ruby logo was designed by David Jones. It is Copyright © 2014 Jerry D'Antonio. All Rights Reserved.