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

  • initializewhich expects two parameters and one block as described below;

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

  • executewhich executes the given block on initialization and updates the counter to the latest timestamp;

  • execute_if_updatedwhich just executes the block if it was updated;

After initialization, a call to execute_if_updatedmust 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 filesarray 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 filesafter initialization to avoid changes that won't make effect.

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

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

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

Execute the block given if updated.

# File activesupport/lib/active_support/file_update_checker.rb, line 84
def execute_if_updated
  if updated?
    execute
    true
  else
    false
  end
end
updated?()

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

# File activesupport/lib/active_support/file_update_checker.rb, line 65
def updated?
  current_updated_at = updated_at
  if @last_update_at < current_updated_at
    @updated_at = updated_at
    true
  else
    false
  end
end