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Active Job

Sometimes a specific piece of code takes a long time to run but doesn’t need to run right away. An example is sending an e-mail after creating an order at the end of a online shopping workflow. It can take a couple of seconds to send an e-mail but you don’t want your user to wait for that to happen within the controller. It makes more sense to use a queueing mechanism for these tasks.

Active Job provides such a queueing system. You can create jobs which are being processed asynchronous by active job.

Create a New Job

The quickest way to create a new job is the job generator. Lets create an example job which waits for 10 seconds and than logs an info message:

$ rails new shop
  [...]
$ cd shop
$ rails generate job example
      invoke  test_unit
      create    test/jobs/example_job_test.rb
      create  app/jobs/example_job.rb
$

All jobs are created in the app/jobs directory. Please change the app/jobs/example_job.rb file accordingly:

app/jobs/example_job.rb
class ExampleJob < ApplicationJob
  queue_as :default

  def perform(*args)
    sleep 10
    logger.info "Just waited 10 seconds."
  end
end

You can test the job in your console with ExampleJob.perform_later which creates it:

$ rails console
Loading development environment (Rails 5.0.0)
>> ExampleJob.perform_later
Performing ExampleJob from Inline(default)
Just waited 10 seconds.
Performed ExampleJob from Inline(default) in 10014.5ms
Enqueued ExampleJob (Job ID: f0b6937d-c2b4-4685-afe3-d571044b57a0) to Inline(default)
=> #<ExampleJob:0x007ffa99a3f020 @arguments=[], @job_id="f0b6937d-c2b4-4685-afe3-d571044b57a0", @queue_name="default", @priority=nil>
>> exit
$

The file log/development.log now contains the logging output.

A more concrete example of using jobs you’ll find in the Action Mailer chapter where an e-mail gets send.

Set the time for future execution

The set method provides two arguments which can be used to set the execution of a job in the future:

  • wait

    ExampleJob.set(wait: 1.hour).perform_later

  • wait_until

    ExampleJob.set(wait_until: Date.tomorrow.noon).perform_later

    == Configure the Job Server Backend

The page http://api.rubyonrails.org/classes/ActiveJob/QueueAdapters.html lists all available backends. To use one of them you have to install the needed gem. Here is an example for the use of the popular Sidekiq. To use the gem you have to add it to Gemfile and run a bundle install afterwards:

Gemfile
[...]
gem 'sidekiq'

In config/application.rb you can configure the use of it:

config/application.rb
require File.expand_path('../boot', __FILE__)

require 'rails/all'

# Require the gems listed in Gemfile, including any gems
# you've limited to :test, :development, or :production.
Bundler.require(*Rails.groups)

module Shop
  class Application < Rails::Application
    # Settings in config/environments/* take precedence over those specified here.
    # Application configuration should go into files in config/initializers
    # -- all .rb files in that directory are automatically loaded.

    config.active_job.queue_adapter = :sidekiq
  end
end