class ActiveSupport::Cache::FileStore

def lock_file(file_name, &block) # :nodoc:
  if File.exist?(file_name)
    File.open(file_name, 'r+') do |f|
      begin
        f.flock File::LOCK_EX
        yield
      ensure
        f.flock File::LOCK_UN
      end
    end
  else
    yield
  end
end