class CGI::Session::FileStore

def update
  return unless @hash
  begin
    lockf = File.open(@path+".lock", File::CREAT|File::RDWR, 0600)
    lockf.flock File::LOCK_EX
    f = File.open(@path+".new", File::CREAT|File::TRUNC|File::WRONLY, 0600)
    for k,v in @hash
      f.printf "%s=%s\n", CGI.escape(k), CGI.escape(String(Marshal.dump(v)))
    end
    f.close
    File.rename @path+".new", @path
  ensure
    f&.close
    lockf&.close
  end
end