protected function _uuid($hex = false)
    {
        $pr_bits = false;

        $fp = @fopen ( '/dev/urandom', 'rb' );
        if ($fp !== false)
        {
            $pr_bits = @fread ( $fp, 16 );
            @fclose ( $fp );
        }

         // If /dev/urandom isn't available (eg: in non-unix systems), use mt_rand().
        if(empty($pr_bits))
        {
            $pr_bits = "";
            for($cnt = 0; $cnt < 16; $cnt ++) {
                $pr_bits .= chr ( mt_rand ( 0, 255 ) );
            }
        }

        $time_low = bin2hex ( substr ( $pr_bits, 0, 4 ) );
        $time_mid = bin2hex ( substr ( $pr_bits, 4, 2 ) );
        $time_hi_and_version = bin2hex ( substr ( $pr_bits, 6, 2 ) );
        $clock_seq_hi_and_reserved = bin2hex ( substr ( $pr_bits, 8, 2 ) );
        $node = bin2hex ( substr ( $pr_bits, 10, 6 ) );

        /**
         * Set the four most significant bits (bits 12 through 15) of the
         * time_hi_and_version field to the 4-bit version number from
         * Section 4.1.3.
         * @see http://tools.ietf.org/html/rfc4122#section-4.1.3
         */
        $time_hi_and_version = hexdec ( $time_hi_and_version );
        $time_hi_and_version = $time_hi_and_version >> 4;
        $time_hi_and_version = $time_hi_and_version | 0x4000;

        /**
         * Set the two most significant bits (bits 6 and 7) of the
         * clock_seq_hi_and_reserved to zero and one, respectively.
         */
        $clock_seq_hi_and_reserved = hexdec ( $clock_seq_hi_and_reserved );
        $clock_seq_hi_and_reserved = $clock_seq_hi_and_reserved >> 2;
        $clock_seq_hi_and_reserved = $clock_seq_hi_and_reserved | 0x8000;

        //Either return as hex or as string
        $format = $hex ? '%08s%04s%04x%04x%012s' : '%08s-%04s-%04x-%04x-%012s';

        return sprintf ( $format, $time_low, $time_mid, $time_hi_and_version, $clock_seq_hi_and_reserved, $node );
    }