girl_friday is a Ruby library for performing asynchronous tasks. Often times you don't want to block a web response by performing some task, like sending an email, so you can just use this gem to perform it in the background. It works with any Ruby application, including Rails 3 applications.

We recommend using JRuby 1.6+ or Rubinius 2.0+ with girl_friday. Both are excellent options for executing Ruby these days.

gem install girl_friday

girl_friday does not support Ruby 1.8 (MRI) because of its lack of native threading. Ruby 1.9.3 will work reasonably well if you use gems that release the GIL for network I/O (mysql2 is a good example of this, do not use the original mysql gem).

Put girl_friday in your Gemfile:

gem 'girl_friday'

In your Rails app, create a config/initializers/girl_friday.rb which defines your queues:

EMAIL_QUEUE = GirlFriday::WorkQueue.new(:user_email, :size => 3) do |msg|
  UserMailer.registration_email(msg).deliver
end

IMAGE_QUEUE = GirlFriday::WorkQueue.new(:image_crawler, :size => 7) do |msg|
  ImageCrawler.process(msg)
end

:size is the number of workers to spin up and defaults to 5. Keep in mind, ActiveRecord defaults to a connection pool size of 5 so if your workers are accessing the database you'll want to ensure that the connection pool is large enough by modifying config/database.yml.

In order to use the Redis backend, you must use a connection pool to share a set of Redis connections with other threads and GirlFriday queues using the connection_pool gem:

require 'connection_pool'

redis_pool = ConnectionPool.new(:size => 5, :timeout => 5) { Redis.new }

CLEAN_FILTER_QUEUE = GirlFriday::WorkQueue.new(:clean_filter, :store => GirlFriday::Store::Redis, :store_config => { :pool => redis_pool }) do |msg|
  Filter.clean(msg)
end

In your controller action or model, you can call #push(msg)

EMAIL_QUEUE.push(:email => @user.email, :name => @user.name)

The msg parameter to push is just a Hash whose contents are completely up to you.

Your message processing block should not access any instance data or variables outside of the block. That's shared mutable state and dangerous to touch! I also strongly recommend your queue processor block be VERY short, ideally just a method call or two. You can unit test those methods easily but not the processor block itself.

You can call GirlFriday::WorkQueue.immediate! to process jobs immediately, which is helpful when testing. GirlFriday::WorkQueue.queue! will revert this & jobs will be processed by actors.

Queues are not garbage collected until they are shutdown, even if you have no reference to them. Make sure you call WorkQueue#shutdown if you are dynamically creating them so you don't leak memory. GirlFriday.shutdown! will shut down all running queues in the process.

Please see the girl_friday wiki for more detail and advanced options and tuning. You'll find details on queue persistence with Redis, implementing clean shutdown, querying runtime metrics and SO MUCH MORE!

From wikipedia:

The term Man Friday has become an idiom, still in mainstream usage, to describe an especially faithful servant or one's best servant or right-hand man. The female equivalent is Girl Friday. The title of the movie His Girl Friday alludes to it and may have popularized it.

Carbon Five, I wrote and maintained girl_friday on their clock.

This gem contains a copy of the Rubinius Actor API, modified to work on any Ruby VM. Thanks to Evan Phoenix, MenTaLguY and the Rubinius project for permission to use and distribute this code.

Mike Perham, @mperham, mikeperham.com