FileUpdateChecker specifies the API used by Rails to watch files and control reloading. The API depends on four methods:

  • initialize which expects two parameters and one block as described below.

  • updated? which returns a boolean if there were updates in the filesystem or not.

  • execute which executes the given block on initialization and updates the latest watched files and timestamp.

  • execute_if_updated which just executes the block if it was updated.

After initialization, a call to execute_if_updated must execute the block only if there was really a change in the filesystem.

This class is used by Rails to reload the I18n framework whenever they are changed upon a new request.

i18n_reloader = ActiveSupport::FileUpdateChecker.new(paths) do
  I18n.reload!
end

ActiveSupport::Reloader.to_prepare do
  i18n_reloader.execute_if_updated
end

Methods

Class Public methods

new(files, dirs = {}, &block)

It accepts two parameters on initialization. The first is an array of files and the second is an optional hash of directories. The hash must have directories as keys and the value is an array of extensions to be watched under that directory.

This method must also receive a block that will be called once a path changes. The array of files and list of directories cannot be changed after FileUpdateChecker has been initialized.

📝 Source code 
# File activesupport/lib/active_support/file_update_checker.rb, line 42
    def initialize(files, dirs = {}, &block)
      unless block
        raise ArgumentError, "A block is required to initialize a FileUpdateChecker"
      end

      @files = files.freeze
      @glob  = compile_glob(dirs)
      @block = block

      @watched    = nil
      @updated_at = nil

      @last_watched   = watched
      @last_update_at = updated_at(@last_watched)
    end
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Instance Public methods

execute()

Executes the given block and updates the latest watched files and timestamp.

📝 Source code 
# File activesupport/lib/active_support/file_update_checker.rb, line 80
    def execute
      @last_watched   = watched
      @last_update_at = updated_at(@last_watched)
      @block.call
    ensure
      @watched = nil
      @updated_at = nil
    end
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execute_if_updated()

Execute the block given if updated.

📝 Source code 
# File activesupport/lib/active_support/file_update_checker.rb, line 90
    def execute_if_updated
      if updated?
        yield if block_given?
        execute
        true
      else
        false
      end
    end
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updated?()

Check if any of the entries were updated. If so, the watched and/or updated_at values are cached until the block is executed via execute or execute_if_updated.

📝 Source code 
# File activesupport/lib/active_support/file_update_checker.rb, line 61
    def updated?
      current_watched = watched
      if @last_watched.size != current_watched.size
        @watched = current_watched
        true
      else
        current_updated_at = updated_at(current_watched)
        if @last_update_at < current_updated_at
          @watched    = current_watched
          @updated_at = current_updated_at
          true
        else
          false
        end
      end
    end
🔎 See on GitHub