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 'unopinionated' 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

Supported Ruby versions

MRI 1.9.3, 2.0, 2.1, 2.2, JRuby (1.9 mode), and Rubinius 2.x are supported. This gem should be fully compatible with any interpreter that is compliant with Ruby 1.9.3 or newer. Java 8 is required for JRuby (Java 7 support is deprecated in version 0.9 and will be removed in 1.0).

Features & Documentation

We have a roadmap guiding our work toward the v1.0.0 release.

The primary site for documentation is the automatically generated API documentation

We also have a mailing list and IRC (gitter).

This library contains a variety of concurrency abstractions at high and low levels. One of the high-level abstractions is likely to meet most common needs.

General-purpose Concurrency Abstractions

  • Async: A mixin module that provides simple asynchronous behavior to any standard class/object or object.
  • Atom: A way to manage shared, synchronous, independent state.
  • Future: An asynchronous operation that produces a value.
    • Dataflow: Built on Futures, Dataflow allows you to create a task that will be scheduled when all of its data dependencies are available.
  • Promise: Similar to Futures, with more features.
  • ScheduledTask: Like a Future scheduled for a specific future time.
  • TimerTask: A Thread that periodically wakes up to perform work at regular intervals.

Thread-safe Value Objects

  • Maybe A thread-safe, immutable object representing an optional value, based on Haskell Data.Maybe.
  • Delay Lazy evaluation of a block yielding an immutable result. Based on Clojure's delay.

Thread-safe Structures

Derived from Ruby's Struct:

  • ImmutableStruct Immutable struct where values are set at construction and cannot be changed later.
  • MutableStruct Synchronized, mutable struct where values can be safely changed at any time.
  • SettableStruct Synchronized, write-once struct where values can be set at most once, either at construction or any time thereafter.

Java-inspired ThreadPools and Other Executors

  • See ThreadPool overview, which also contains a list of other Executors available.

Thread Synchronization Classes and Algorithms

Thread-safe Variables

Edge Features

These are available in the concurrent-ruby-edge companion gem, installed with gem install concurrent-ruby-edge.

These features are under active development and may change frequently. They are expected not to keep backward compatibility (there may also lack tests and documentation). Semantic versions will be obeyed though. Features developed in concurrent-ruby-edge are expected to move to concurrent-ruby when final.

  • Actor: Implements the Actor Model, where concurrent actors exchange messages.
  • new Future Framework - new unified implementation of Futures and Promises which combines Features of previous Future, Promise, IVar, Event, Probe, dataflow, Delay, TimerTask into single framework. It uses extensively new synchronization layer to make all the features non-blocking and lock-free with exception of obviously blocking operations like #wait, #value. It also offers better performance.
  • Agent: A single atomic value that represents an identity.
  • Channel: Communicating Sequential Processes (CSP).
  • Exchanger
  • LazyRegister
  • Atomic Markable Reference
  • LockFreeLinked Set
  • LockFreeStack


Why are these not in core?

  • Actor - Partial documentation and tests; stability is good.
  • Future/Promise Framework - API changes; partial documentation and tests; stability good.
  • Agent - Incomplete behaviour compared to Clojure's models; stability good.
  • Channel - Missing documentation; limted features; stability good.
  • Exchanger - Known race condition requiring a new implementation.
  • LazyRegister - Missing documentation and tests.
  • AtomicMarkableReference, LockFreeLinkedSet, LockFreeStack - Needs real world battle testing


All abstractions within this gem can be loaded simply by requiring it:

require 'concurrent'

To reduce the amount of code loaded at runtime, subsets of this gem can be required:

require 'concurrent'                # everything

# groups

require 'concurrent/atomics'        # atomic and thread synchronization classes
require 'concurrent/executors'      # Thread pools and other executors

# individual abstractions

require 'concurrent/async'            # Concurrent::Async
require 'concurrent/atom'             # Concurrent::Atom
require 'concurrent/dataflow'         # Concurrent::dataflow
require 'concurrent/delay'            # Concurrent::Delay
require 'concurrent/future'           # Concurrent::Future
require 'concurrent/immutable_struct' # Concurrent::ImmutableStruct
require 'concurrent/ivar'             # Concurrent::IVar
require 'concurrent/maybe'            # Concurrent::Maybe
require 'concurrent/mutable_struct'   # Concurrent::MutableStruct
require 'concurrent/mvar'             # Concurrent::MVar
require 'concurrent/promise'          # Concurrent::Promise
require 'concurrent/scheduled_task'   # Concurrent::ScheduledTask
require 'concurrent/settable_struct'  # Concurrent::SettableStruct
require 'concurrent/timer_task'       # Concurrent::TimerTask
require 'concurrent/tvar'             # Concurrent::TVar

# experimental - available in `concurrent-ruby-edge` companion gem

require 'concurrent/actor'          # Concurrent::Actor and supporting code
require 'concurrent/edge/future'    # new Future Framework
require 'concurrent/agent'          # Concurrent::Agent
require 'concurrent/channel '       # Concurrent::Channel and supporting code

If the library does not behave as expected, Concurrent.use_stdlib_logger(Logger::DEBUG) could help to reveal the problem.


gem install concurrent-ruby

or add the following line to Gemfile:

gem 'concurrent-ruby'

and run bundle install from your shell.

C Extensions for MRI

Potential performance improvements may be achieved under MRI by installing optional C extensions. To minimize installation errors the C extensions are available in the concurrent-ruby-ext extension gem. concurrent-ruby and concurrent-ruby-ext are always released together with same version. Simply install the extension gem too:

gem install concurrent-ruby-ext

or add the following line to Gemfile:

gem 'concurrent-ruby-ext'

and run bundle install from your shell.

In code it is only necessary to

require 'concurrent'

The concurrent-ruby gem will automatically detect the presence of the concurrent-ruby-ext gem and load the appropriate C extensions.

Note For gem developers

No gems should depend on concurrent-ruby-ext. Doing so will force C extensions on your users. The best practice is to depend on concurrent-ruby and let users to decide if they want C extensions.


All published versions of this gem (core, extension, and several platform-specific packages) are compiled, packaged, tested, and published using an open, automated process. This process can also be used to create pre-compiled binaries of the extension gem for virtally any platform. Documentation is forthcoming...

*MRI only*
bundle exec rake build:native       # Build concurrent-ruby-ext-<version>-<platform>.gem into the pkg dir
bundle exec rake compile:extension  # Compile extension

*JRuby only*
bundle exec rake build              # Build JRuby-specific core gem (alias for `build:core`)
bundle exec rake build:core         # Build concurrent-ruby-<version>-java.gem into the pkg directory

*All except JRuby*
bundle exec rake build:core         # Build concurrent-ruby-<version>.gem into the pkg directory
bundle exec rake build:ext          # Build concurrent-ruby-ext-<version>.gem into the pkg directory

*When Docker IS installed*
bundle exec rake build:windows      # Build the windows binary <version> gems per rake-compiler-dock
bundle exec rake build              # Build core, extension, and edge gems, including Windows binaries

*When Docker is NOT installed*
bundle exec rake build              # Build core, extension, and edge gems (excluding Windows binaries)

bundle exec rake clean              # Remove any temporary products
bundle exec rake clobber            # Remove any generated file
bundle exec rake compile            # Compile all the extensions



  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

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.