code: public function spawn()
      {
          $needToStart = $this->processes - count($this->workers);
          $this->logger->debug("will start {$needToStart} processes");
          for ($i = 0; $i < $needToStart; $i++) {
              $worker = $this->spawnWorker();
              $this->didSpawnWorker($worker, $i);
              $worker->start();
              $this->workers[] = $worker;
          }
      }
docs: 启动新进程
  
  @return void