lock_file

# File activesupport/lib/active_support/cache/file_store.rb, line 137
        def lock_file(file_name, &block)
          if File.exist?(file_name)
            File.open(file_name, "r+") do |f|
              f.flock File::LOCK_EX
              yield
            ensure
              f.flock File::LOCK_UN
            end
          else
            yield
          end
        end