Nsqd 的启动借助了srv的包，srv定义的service接口包括以下方法

type Service interface {
    // Init is called before the program/service is started and after it's
    // determined if the program is running as a Windows Service.
    Init(Environment) error

    // Start is called after Init. This method must be non-blocking.
    Start() error

    // Stop is called in response to os.Interrupt, os.Kill, or when a
    // Windows Service is stopped.
    Stop() error
}

srv 在启动的时候依次调用这几个函数实现；并注册了信号，实现优雅的关闭服务

func Run(service Service, sig ...os.Signal) error {
    env := environment{}
    if err := service.Init(env); err != nil {
        return err
    }

    if err := service.Start(); err != nil {
        return err
    }

    if len(sig) == 0 {
        sig = []os.Signal{syscall.SIGINT, syscall.SIGTERM}
    }

    signalChan := make(chan os.Signal, 1)
    signalNotify(signalChan, sig...)
    <-signalChan

    return service.Stop()
}

1. program的启动首先加载命令行参数和配置的参数合并

2. 创建nsqd,创建过程中对配置的dataPath上锁，直至系统推出
   同样配置下启动另外一个nsqd将获取锁失败

   
   截屏2020-02-2315.20.53.png

3. 调用nsqd.Main，启动httpserver和tcpserver

系统退出

• 先关闭tcp和http的监听套接字
• 存储元数据
• 关闭topic
• 等待其他的协程结束
• 解锁文件锁

func (n *NSQD) Exit() {
    if n.tcpListener != nil {
        n.tcpListener.Close()
    }
    if n.tcpServer != nil {
        n.tcpServer.CloseAll()
    }

    if n.httpListener != nil {
        n.httpListener.Close()
    }

    if n.httpsListener != nil {
        n.httpsListener.Close()
    }
      
    n.Lock()
        // 存储元数据，再次启动将获取元数据
    err := n.PersistMetadata()
    if err != nil {
        n.logf(LOG_ERROR, "failed to persist metadata - %s", err)
    }
    n.logf(LOG_INFO, "NSQ: closing topics")
       // 关闭所有的topic，不再推送数据到客户端
    for _, topic := range n.topicMap {
        topic.Close()
    }
    n.Unlock()
      
    n.logf(LOG_INFO, "NSQ: stopping subsystems")
    close(n.exitChan)
    n.waitGroup.Wait()
    n.dl.Unlock()
    n.logf(LOG_INFO, "NSQ: bye")
}