worker.unref()

对 worker 调用 unref() 可以使线程在事件系统中这是唯一活动句柄时退出。如果 worker 已经被 unref()，再次调用 unref() 则没有效果。

【Calling unref() on a worker allows the thread to exit if this is the only active handle in the event system. If the worker is already unref()ed calling unref() again has no effect.】