# class ActiveSupport::FileUpdateChecker

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

### Public Class Methods

new(files, dirs={}, &block) click to toggle source

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.

    # File 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

### Public Instance Methods

execute() click to toggle source

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

    # File 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() click to toggle source

Execute the block given if updated.

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

updated?() click to toggle source

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`

    # File 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