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Module: ActiveSupport::LazyLoadHooks

Relationships & Source Files
Extension / Inclusion / Inheritance Descendants
Extended In:
::ActiveSupport
Defined in: activesupport/lib/active_support/lazy_load_hooks.rb

Overview

Lazy Load Hooks

LazyLoadHooks allows Rails to lazily load a lot of components and thus making the app boot faster. Because of this feature now there is no need to require ::ActiveRecord::Base at boot time purely to apply configuration. Instead a hook is registered that applies configuration once ::ActiveRecord::Base is loaded. Here ::ActiveRecord::Base is used as example but this feature can be applied elsewhere too.

Here is an example where on_load method is called to register a hook.

initializer 'active_record.initialize_timezone' do
  ActiveSupport.on_load(:active_record) do
    self.time_zone_aware_attributes = true
    self.default_timezone = :utc
  end
end

When the entirety of ::ActiveRecord::Base has been evaluated then run_load_hooks is invoked. The very last line of ::ActiveRecord::Base is:

ActiveSupport.run_load_hooks(:active_record, ActiveRecord::Base)

run_load_hooks will then execute all the hooks that were registered with the on_load method. In the case of the above example, it will execute the block of code that is in the initializer.

Registering a hook that has already run results in that hook executing immediately. This allows hooks to be nested for code that relies on multiple lazily loaded components:

initializer "action_text.renderer" do
  ActiveSupport.on_load(:action_controller_base) do
    ActiveSupport.on_load(:action_text_content) do
      self.default_renderer = Class.new(ActionController::Base).renderer
    end
  end
end

Class Method Summary

Instance Method Summary

Class Method Details

.extended(base)

This method is for internal use only.
[ GitHub ] 

  


# File 'activesupport/lib/active_support/lazy_load_hooks.rb', line 44



def self.extended(base) # :nodoc:
  base.class_eval do
    @load_hooks = Hash.new { |h, k| h[k] = [] }
    @loaded     = Hash.new { |h, k| h[k] = [] }
    @run_once   = Hash.new { |h, k| h[k] = [] }
  end
end


  







Instance Method Details



  

    #execute_hook(name, base, options, block)   (private)
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/lazy_load_hooks.rb', line 91



def execute_hook(name, base, options, block)
  with_execution_control(name, block, options[:run_once]) do
    if options[:yield]
      block.call(base)
    else
      if base.is_a?(Module)
        base.class_eval(&block)
      else
        base.instance_eval(&block)
      end
    end
  end
end


  








  

    #on_load(name, options = {}, &block)  
  



  

    

Declares a block that will be executed when a Rails component is fully loaded. If the component has already loaded, the block is executed immediately.



Options:


  • 

    :yield - Yields the object that run_load_hooks to block.
    

  • 

    :run_once - Given block will run only once.
    



  



  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/lazy_load_hooks.rb', line 60



def on_load(name, options = {}, &block)
  @loaded[name].each do |base|
    execute_hook(name, base, options, block)
  end

  @load_hooks[name] << [block, options]
end


  








  

    #run_load_hooks(name, base = Object)  
  



  

    

Executes all blocks registered to name via on_load, using base as the evaluation context.



ActiveSupport.run_load_hooks(:active_record, ActiveRecord::Base)



In the case of the above example, it will execute all hooks registered for :active_record within the class ::ActiveRecord::Base.


  



  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/lazy_load_hooks.rb', line 75



def run_load_hooks(name, base = Object)
  @loaded[name] << base
  @load_hooks[name].each do |hook, options|
    execute_hook(name, base, options, hook)
  end
end


  








  

    #with_execution_control(name, block, once)   (private)
  

  [ GitHub ]


  

  


# File 'activesupport/lib/active_support/lazy_load_hooks.rb', line 83



def with_execution_control(name, block, once)
  unless @run_once[name].include?(block)
    @run_once[name] << block if once

    yield
  end
end