private function elapsedTime( $index = 'utime')
	{
		if ( version_compare( PHP_VERSION, "7.0", "<" ) ) return;

		$rus = $this->rustart;
		$ru = getrusage();
		return ( $ru[ "ru_$index.tv_sec" ] * 1000 + intval( $ru[ "ru_$index.tv_usec" ] / 1000 ) ) - ( $rus[ "ru_$index.tv_sec" ] * 1000 + intval( $rus[ "ru_$index.tv_usec" ] / 1000 ) );
	}