public function debugLogCPU($message='')
  {
    // get resource usage
    $dat = getrusage();
    $message.='[u:'.substr(($dat["ru_utime.tv_sec"]*1e6+$dat["ru_utime.tv_usec"])-$this->startUserCPU,0,-3).'ms / s:'.substr(($dat["ru_stime.tv_sec"]*1e6+$dat["ru_stime.tv_usec"])-$this->startSystemCPU,0,-3).'ms]';
    $this->debugLog($message);
  }