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 counter to the latest 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.

Examples

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

  ActionDispatch::Reloader.to_prepare do
    i18n_reloader.execute_if_updated
  end
Methods
E
N
U
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.

Implementation details

This particular implementation checks for added and updated files, but not removed files. Directories lookup are compiled to a glob for performance. Therefore, while someone can add new files to the files array after initialization (and parts of Rails do depend on this feature), adding new directories after initialization is not allowed.

Notice that other objects that implements FileUpdateChecker API may not even allow new files to be added after initialization. If this is the case, we recommend freezing the files after initialization to avoid changes that won’t make effect.

Source: show | on GitHub 

    # File activesupport/lib/active_support/file_update_checker.rb, line 55
55:     def initialize(files, dirs={}, &block)
56:       @files = files
57:       @glob  = compile_glob(dirs)
58:       @block = block
59:       @updated_at = nil
60:       @last_update_at = updated_at
61:     end
Instance Public methods
execute()

Executes the given block and updates the counter to latest timestamp.

Source: show | on GitHub 

    # File activesupport/lib/active_support/file_update_checker.rb, line 76
76:     def execute
77:       @last_update_at = updated_at
78:       @block.call
79:     ensure
80:       @updated_at = nil
81:     end
execute_if_updated()

Execute the block given if updated.

Source: show | on GitHub 

    # File activesupport/lib/active_support/file_update_checker.rb, line 84
84:     def execute_if_updated
85:       if updated?
86:         execute
87:         true
88:       else
89:         false
90:       end
91:     end
updated?()

Check if any of the entries were updated. If so, the updated_at value is cached until the block is executed via execute or execute_if_updated

Source: show | on GitHub 

    # File activesupport/lib/active_support/file_update_checker.rb, line 65
65:     def updated?
66:       current_updated_at = updated_at
67:       if @last_update_at < current_updated_at
68:         @updated_at = updated_at
69:         true
70:       else
71:         false
72:       end
73:     end