protected function handleMessage(IWorker $worker, IMessage $message)
 {
     echo 'Receive: ' . $message->type . ' (workerID = ' . $worker->getInternalID() . ')<br>';
     switch ($message->type) {
         case self::MESSAGE_TYPE_PONG:
             $this->sendPing($worker);
             break;
         default:
             break;
     }
 }
 /**
  * Returns last known worker state from worker state list or null if it is unknown
  * @return array|null state of calculation in child process
  */
 private function getWorkerState(IWorker $worker)
 {
     $workerID = $worker->getInternalID();
     if (isset($this->workerStateList[$workerID])) {
         return $this->workerStateList[$workerID];
     }
     return null;
 }