update

# File lib/cgi/session.rb, line 417
      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 if f
          lockf.close if lockf
        end
      end