cluster.fork([env])

• env <Object> 要添加到工作进程环境变量的键/值对。

  ¥env <Object> Key/value pairs to add to worker process environment.

• 返回：<cluster.Worker>

  ¥Returns: <cluster.Worker>

衍生新的工作进程。

¥Spawn a new worker process.

这只能从主进程调用。

¥This can only be called from the primary process.