code: private function handleProcessExitStatus(int $pid, int $childType, int $exitStatus)
      {
          switch ($childType) {
              case self::PROCESS_TYPE_JOB:
                  $childType = 'Child';
                  break;
              default:
                  $childType = 'Watchdog';
          }
  
          if ($exitStatus === 0) {
              $this->logger->debug("{type}: {$childType} process exited successfully", $this->logContext);
              return false;
          }
  
          $error = $this->readErrorFromSocket($this->sockets[$pid]);
          $jobFailedMessage = $error ?: "{$childType} process failed with status: {$exitStatus}";
  
          $this->logger->error("{type}: fatal error in {$childType} process: {$jobFailedMessage}", $this->logContext);
  
          return $jobFailedMessage;
      }
docs: Handle process exit status.
  
  @param int $pid
  @param int $childType
  @param int $exitStatus
  
  @return false|string FALSE if exit status indicates success; otherwise, a string containing the error messages.