class ActiveSupport::EventedFileUpdateChecker

def initialize(files, dirs = {}, &block)

:nodoc: all

# => "changed"
checker.execute_if_updated
# => true
checker.updated?

FileUtils.touch("/tmp/foo")

# => nil
checker.execute_if_updated
# => false
checker.updated?
checker = EventedFileUpdateChecker.new(["/tmp/foo"], -> { puts "changed" })

Example:

Note: Forking will cause the first call to `updated?` to return `true`.

is run and there have been changes to the file system.
EventedFileUpdateChecker#execute is run or when EventedFileUpdateChecker#execute_if_updated
and file extensions to watch. It also takes a block that is called when
The file checker takes an array of files to watch or a hash specifying directories

in state.
instead it uses platform specific file system events to trigger a change
The evented file updater does not hit disk when checking for updates
Allows you to "listen" to changes in a file system. 
def initialize(files, dirs = {}, &block)
  @ph    = PathHelper.new
  @files = files.map { |f| @ph.xpath(f) }.to_set
  @dirs = {}
  dirs.each do |dir, exts|
    @dirs[@ph.xpath(dir)] = Array(exts).map { |ext| @ph.normalize_extension(ext) }
  end
  @block      = block
  @updated    = Concurrent::AtomicBoolean.new(false)
  @lcsp       = @ph.longest_common_subpath(@dirs.keys)
  @pid        = Process.pid
  @boot_mutex = Mutex.new
  if (@dtw = directories_to_watch).any?
    # Loading listen triggers warnings. These are originated by a legit
    # usage of attr_* macros for private attributes, but adds a lot of noise
    # to our test suite. Thus, we lazy load it and disable warnings locally.
    silence_warnings do
      begin
        require 'listen'
      rescue LoadError => e
        raise LoadError, "Could not load the 'listen' gem. Add `gem 'listen'` to the development group of your Gemfile", e.backtrace
      end
    end
  end
  boot!
end