rails/actionpack/lib/action_controller/caching.rb

require 'fileutils'
require 'uri'
require 'set'

module ActionController #:nodoc:
  # Caching is a cheap way of speeding up slow applications by keeping the result of calculations, renderings, and database calls
  # around for subsequent requests. Action Controller affords you three approaches in varying levels of granularity: Page, Action, Fragment.
  #
  # You can read more about each approach and the sweeping assistance by clicking the modules below.
  #
  # Note: To turn off all caching and sweeping, set Base.perform_caching = false.
  #
  #
  # == Caching stores
  #
  # All the caching stores from ActiveSupport::Cache are available to be used as backends for Action Controller caching. This setting only
  # affects action and fragment caching as page caching is always written to disk.
  #
  # Configuration examples (MemoryStore is the default):
  #
  #   ActionController::Base.cache_store = :memory_store
  #   ActionController::Base.cache_store = :file_store, "/path/to/cache/directory"
  #   ActionController::Base.cache_store = :drb_store, "druby://localhost:9192"
  #   ActionController::Base.cache_store = :mem_cache_store, "localhost"
  #   ActionController::Base.cache_store = MyOwnStore.new("parameter")
  module Caching
    extend ActiveSupport::Concern

    autoload :Actions, 'action_controller/caching/actions'
    autoload :Fragments, 'action_controller/caching/fragments'
    autoload :Pages, 'action_controller/caching/pages'
    autoload :Sweeper, 'action_controller/caching/sweeping'
    autoload :Sweeping, 'action_controller/caching/sweeping'

    included do
      @@cache_store = nil
      cattr_reader :cache_store

      # Defines the storage option for cached fragments
      def self.cache_store=(store_option)
        @@cache_store = ActiveSupport::Cache.lookup_store(store_option)
      end

      include Pages, Actions, Fragments
      include Sweeping if defined?(ActiveRecord)

      @@perform_caching = true
      cattr_accessor :perform_caching

      def self.cache_configured?
        perform_caching && cache_store
      end
    end

    protected
      # Convenience accessor
      def cache(key, options = {}, &block)
        if cache_configured?
          cache_store.fetch(ActiveSupport::Cache.expand_cache_key(key, :controller), options, &block)
        else
          yield
        end
      end

    private
      def cache_configured?
        self.class.cache_configured?
      end
  end
end