The documentation for Queue Adapters enumerates a list of supported backends. The last 2 rows of a table mention built-in adapters: Active Job Inline and Active Job. The last one is mentioned as asynchronous. The question is: where can I find the implementation of this adapter and how do I set up my application to use it?

As far as I can see now, there are following modules being included:

  module QueueAdapters
    extend ActiveSupport::Autoload

    autoload :InlineAdapter
    autoload :BackburnerAdapter
    autoload :DelayedJobAdapter
    autoload :QuAdapter
    autoload :QueAdapter
    autoload :QueueClassicAdapter
    autoload :ResqueAdapter
    autoload :SidekiqAdapter
    autoload :SneakersAdapter
    autoload :SuckerPunchAdapter
    autoload :TestAdapter
  end

Ok, I see Inline adapter. But I see no Async one.

This is pretty confusing. Am I missing something obvious?