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+Active Job Basics
+=================
+
+This guide provides you with all you need to get started in creating,
+enqueueing and executing background jobs.
+
+After reading this guide, you will know:
+
+* How to create jobs.
+* How to enqueue jobs.
+* How to run jobs in the background.
+* How to send emails from your application async.
+
+--------------------------------------------------------------------------------
+
+
+Introduction
+------------
+
+Active Job is a framework for declaring jobs and making them run on a variety
+of queueing backends. These jobs can be everything from regularly scheduled
+clean-ups, to billing charges, to mailings. Anything that can be chopped up
+into small units of work and run in parallel, really.
+
+
+The Purpose of the Active Job
+-----------------------------
+The main point is to ensure that all Rails apps will have a job infrastructure
+in place, even if it's in the form of an "immediate runner". We can then have
+framework features and other gems build on top of that, without having to
+worry about API differences between various job runners such as Delayed Job
+and Resque. Picking your queuing backend becomes more of an operational concern,
+then. And you'll be able to switch between them without having to rewrite your jobs.
+
+
+Creating a Job
+--------------
+
+This section will provide a step-by-step guide to creating a job and enqueuing it.
+
+### Create the Job
+
+Active Job provides a Rails generator to create jobs. The following will create a
+job in `app/jobs`:
+
+```bash
+$ bin/rails generate job guests_cleanup
+create  app/jobs/guests_cleanup_job.rb
+```
+
+You can also create a job that will run on a specific queue:
+
+```bash
+$ bin/rails generate job guests_cleanup --queue urgent
+create  app/jobs/guests_cleanup_job.rb
+```
+
+As you can see, you can generate jobs just like you use other generators with
+Rails.
+
+If you don't want to use a generator, you could create your own file inside of
+`app/jobs`, just make sure that it inherits from `ActiveJob::Base`.
+
+Here's what a job looks like:
+
+```ruby
+class GuestsCleanupJob < ActiveJob::Base
+  queue_as :default
+
+  def perform(*args)
+    # Do something later
+  end
+end
+```
+
+### Enqueue the Job
+
+Enqueue a job like so:
+
+```ruby
+MyJob.perform_later record  # Enqueue a job to be performed as soon the queueing system is free.
+```
+
+```ruby
+MyJob.set(wait_until: Date.tomorrow.noon).perform_later(record)  # Enqueue a job to be performed tomorrow at noon.
+```
+
+```ruby
+MyJob.set(wait: 1.week).perform_later(record) # Enqueue a job to be performed 1 week from now.
+```
+
+That's it!
+
+
+Job Execution
+-------------
+
+If no adapter is set, the job is immediately executed.
+
+### Backends
+
+Active Job has built-in adapters for multiple queueing backends (Sidekiq,
+Resque, Delayed Job and others). To get an up-to-date list of the adapters
+see the API Documentation for [ActiveJob::QueueAdapters](http://api.rubyonrails.org/classes/ActiveJob/QueueAdapters.html).
+
+### Changing the Backend
+
+You can easily change your queueing backend:
+
+```ruby
+# be sure to have the adapter gem in your Gemfile and follow the adapter specific
+# installation and deployment instructions
+Rails.application.config.active_job.queue_adapter = :sidekiq
+```
+
+
+Queues
+------
+
+Most of the adapters support multiple queues. With Active Job you can schedule
+the job to run on a specific queue:
+
+```ruby
+class GuestsCleanupJob < ActiveJob::Base
+  queue_as :low_priority
+  #....
+end
+```
+
+You can prefix the queue name for all your jobs using
+`config.active_job.queue_name_prefix` in `application.rb`:
+
+```ruby
+# config/application.rb
+module YourApp
+  class Application < Rails::Application
+    config.active_job.queue_name_prefix = Rails.env
+  end
+end
+
+# app/jobs/guests_cleanup.rb
+class GuestsCleanupJob < ActiveJob::Base
+  queue_as :low_priority
+  #....
+end
+
+# Now your job will run on queue production_low_priority on your
+# production environment and on beta_low_priority on your beta
+# environment
+```
+
+If you want more control on what queue a job will be run you can pass a :queue
+option to #set:
+
+```ruby
+MyJob.set(queue: :another_queue).perform_later(record)
+```
+
+To control the queue from the job level you can pass a block to queue_as. The
+block will be executed in the job context (so you can access self.arguments)
+and you must return the queue name:
+
+```ruby
+class ProcessVideoJob < ActiveJob::Base
+  queue_as do
+    video = self.arguments.first
+    if video.owner.premium?
+      :premium_videojobs
+    else
+      :videojobs
+    end
+  end
+
+  def perform(video)
+    # do process video
+  end
+end
+
+ProcessVideoJob.perform_later(Video.last)
+```
+
+
+NOTE: Make sure your queueing backend "listens" on your queue name. For some
+backends you need to specify the queues to listen to.
+
+
+Callbacks
+---------
+
+Active Job provides hooks during the lifecycle of a job. Callbacks allow you to
+trigger logic during the lifecycle of a job.
+
+### Available callbacks
+
+* `before_enqueue`
+* `around_enqueue`
+* `after_enqueue`
+* `before_perform`
+* `around_perform`
+* `after_perform`
+
+### Usage
+
+```ruby
+class GuestsCleanupJob < ActiveJob::Base
+  queue_as :default
+
+  before_enqueue do |job|
+    # do something with the job instance
+  end
+
+  around_perform do |job, block|
+    # do something before perform
+    block.call
+    # do something after perform
+  end
+
+  def perform
+    # Do something later
+  end
+end
+```
+
+
+ActionMailer
+------------
+
+One of the most common jobs in a modern web application is sending emails outside
+of the request-response cycle, so the user doesn't have to wait on it. Active Job
+is integrated with Action Mailer so you can easily send emails asynchronously:
+
+```ruby
+# If you want to send the email now use #deliver_now
+UserMailer.welcome(@user).deliver_now
+
+# If you want to send the email through Active Job use #deliver_later
+UserMailer.welcome(@user).deliver_later
+```
+
+
+GlobalID
+--------
+Active Job supports GlobalID for parameters. This makes it possible to pass live
+Active Record objects to your job instead of class/id pairs, which you then have
+to manually deserialize. Before, jobs would look like this:
+
+```ruby
+class TrashableCleanupJob
+  def perform(trashable_class, trashable_id, depth)
+    trashable = trashable_class.constantize.find(trashable_id)
+    trashable.cleanup(depth)
+  end
+end
+```
+
+Now you can simply do:
+
+```ruby
+class TrashableCleanupJob
+  def perform(trashable, depth)
+    trashable.cleanup(depth)
+  end
+end
+```
+
+This works with any class that mixes in `ActiveModel::GlobalIdentification`, which
+by default has been mixed into Active Model classes.
+
+
+Exceptions
+----------
+
+Active Job provides a way to catch exceptions raised during the execution of the
+job:
+
+```ruby
+
+class GuestsCleanupJob < ActiveJob::Base
+  queue_as :default
+
+  rescue_from(ActiveRecord::RecordNotFound) do |exception|
+   # do something with the exception
+  end
+
+  def perform
+    # Do something later
+  end
+end
+```