Celluloid: Actor-based concurrent object framework for Ruby

NOTE: This is the 0.18.x development branch of Celluloid. For the 0.17.x stable branch, please see:

https://github.com/celluloid/celluloid/tree/0-17-stable

"I thought of objects being like biological cells and/or individual computers on a network, only able to communicate with messages" --Alan Kay, creator of Smalltalk, on the meaning of "object oriented programming"

Celluloid provides a simple and natural way to build fault-tolerant concurrent programs in Ruby. With Celluloid, you can build systems out of concurrent objects just as easily as you build sequential programs out of regular objects. Recommended for any developer, including novices, Celluloid should help ease your worries about building multithreaded Ruby programs.

Motivation

Much of the difficulty with building concurrent programs in Ruby arises because the object-oriented mechanisms for structuring code, such as classes and inheritance, are separate from the concurrency mechanisms, such as threads and locks. Celluloid combines these into a single structure, an active object running within a thread, called an "actor", or in Celluloid vernacular, a "cell".

By combining concurrency with object oriented programming, Celluloid frees you up from worry about where to use threads and locks. Celluloid combines them together into a single concurrent object oriented programming model, encapsulating state in concurrent objects and thus avoiding many of the problems associated with multithreaded programming. Celluloid provides many features which make concurrent programming simple, easy, and fun:

• Automatic "deadlock-free" synchronization:Celluloid uses a concurrent object model which combines method dispatch and thread synchronization. Each actor is a concurrent object running in its own thread, and every method invocation is wrapped in a fiber that can be suspended whenever it calls out to other actors, and resumed when the response is available. This means methods which are waiting for responses from other actors, external messages, or other system events (including I/O with Celluloid::IO) can be suspended and will never block other methods that are ready to run. This won't prevent bugs in Celluloid, bugs in other thread-safe libraries you use, and even certain "dangerous" features of Celluloid from causing your program to deadlock, but in general, programs built with Celluloid will be naturally immune to deadlocks.

• Fault-tolerance:Celluloid has taken to heart many of Erlang's ideas about fault-tolerance in order to enable self-healing applications. The central idea: have you tried turning it off and on again? Celluloid takes care of rebooting subcomponents of your application when they crash, whether it's a single actor, or large (potentially multi-tiered) groups of actors that are all interdependent. This means rather than worrying about rescuing every last exception, you can just sit back, relax, and let parts of your program crash, knowing Celluloid will automatically reboot them in a clean state. Celluloid provides its own implementation of the core fault-tolerance concepts in Erlang including linking , supervisors , and supervision groups .

• Futures : Ever wanted to call a method "in the background" and retrieve the value it returns later? Celluloid futures do just that. It's like calling ahead to a restaurant to place an order, so they can work on preparing your food while you're on your way to pick it up. When you ask for a method's return value, it's returned immediately if the method has already completed, or otherwise the current method is suspended until the value becomes available.

You can also build distributed systems with Celluloid using its sister project DCell . Evented IO similar to EventMachine (with a synchronous API instead of callback/deferrable soup) is available through the Celluloid::IO library.

Is it any good?

Yes

Is It "Production Ready™"?

Yes, many users are now running Celluloid in production.

• See: Projects Using Celluloid

Discussion

Like Celluloid? Join the mailing list/Google Group or visit us on IRC at #celluloid on freenode

Documentation

Please see the Celluloid Wiki for more detailed documentation and usage notes.

The following API documentation is also available:

• YARD API documentation
• Celluloid module (primary API)
• Celluloid class methods
• All Celluloid classes

Related Projects

Celluloid is the parent project of a related ecosystem of other projects. If you like Celluloid we definitely recommend you check them out:

• Reel : An "evented" web server based on Celluloid::IO
• DCell : The Celluloid actor protocol distributed over 0MQ
• ECell : Mesh strategies for Celluloid actors distributed over 0MQ
• Celluloid::IO : "Evented" IO support for Celluloid actors
• Celluloid::ZMQ : "Evented" 0MQ support for Celluloid actors
• Celluloid::DNS : An "evented" DNS server based on Celluloid::IO
• Celluloid::SMTP : An "evented" SMTP server based on Celluloid::IO
• Lattice : A concurrent realtime web framework based on Celluloid::IO
• nio4r : "New IO for Ruby": high performance IO selectors
• Timers : A generic Ruby timer library for event-based systems

Installation

Add this line to your application's Gemfile:

gem 'celluloid'

And then execute:

$ bundle

Or install it yourself as:

$ gem install celluloid

Require Celluloid with:

require 'celluloid'

Supported Platforms

This library aims to support and is tested against the following Ruby versions:

• Ruby 2.2.6+
• Ruby 2.3.0+
• JRuby 9.1.6.0+

If something doesn't work on one of these versions, it's a bug.

This library may inadvertently work (or seem to work) on other Ruby versions, however support will only be provided for the versions listed above.

If you would like this library to support another Ruby version or implementation, you may volunteer to be a maintainer. Being a maintainer entails making sure all tests run and pass on that implementation. When something breaks on your implementation, you will be responsible for providing patches in a timely fashion. If critical issues for a particular implementation exist at the time of a major release, support for that Ruby version may be dropped.

Additional Reading

• Concurrent Object-Oriented Programming in Python with ATOM a similar system to Celluloid written in Python

Contributing to Celluloid

• Fork this repository on github
• Make your changes and send us a pull request
• If we like them we'll merge them
• If we've accepted a patch, feel free to ask for commit access

License

Copyright (c) 2011-2016 Tony Arcieri, Donovan Keme.

Distributed under the MIT License. See LICENSE.txt for further details.