聊一聊Go服务的优雅处理(二)--优雅重启

func control(network, address string, c syscall.RawConn) error {
	var err error
	c.Control(func(fd uintptr) {
		err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEADDR, 1)
		if err != nil {
			return
		}
		err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEPORT, 1)
		if err != nil {
			return
		}
	})
	return err
}

func listener() (net.Listener, error) {
	lc := net.ListenConfig{
		Control: control,
	}
	if l, err := lc.Listen(context.TODO(), "tcp", ":8080"); err != nil {
	    // 端口未使用，返回err
		return nil, err
	} else {
		return l, nil
	}
}

func upgradeLoop(l *net.Listener, s *http.Server) {
	sig := make(chan os.Signal)
	signal.Notify(sig, syscall.SIGQUIT, syscall.SIGUSR2)
	for t := range sig {
		switch t {
		case syscall.SIGUSR2:
			// 接收升级信号量
			log.Println("Received SIGUSR2 upgrading binary")
			// Fork子进程优雅升级
			if err := spawnChild(); err != nil {
				log.Println(
					"Cannot perform binary upgrade, when starting process: ",
					err.Error(),
				)
				continue
			}
		case syscall.SIGQUIT:
		    // 接收杀掉当前进程的信号量
			s.Shutdown(context.Background())
			os.Exit(0)
		}
	}
}

// fork创建子进程，并在新进程之前更新覆盖全局父进程id
func spawnChild() error {
	// 获取当前启动传入可执行文件参数, 如./main
	argv0, err := exec.LookPath(os.Args[0])
	if err != nil {
		return err
	}
	wd, err := os.Getwd()
	if err != nil {
		return err
	}

	files := make([]*os.File, 0)
	files = append(files, os.Stdin, os.Stdout, os.Stderr)

	// 存下当前进程, 这个id会在新进程启动之后kill掉
	ppid := os.Getpid()
	os.Setenv("APP_PPID", strconv.Itoa(ppid))

	// 启动新进程
	os.StartProcess(argv0, os.Args, &os.ProcAttr{
		Dir:   wd,
		Env:   os.Environ(),
		Files: files,
		Sys:   &syscall.SysProcAttr{},
	})

	return nil
}

func main() {
	log.Println("Started HTTP API, PID: ", os.Getpid())
	var l net.Listener
    // 首次启动
    if fd, err := listener(); err != nil {
    	log.Println("Parent does not exists, starting a normal way")
    	l, err = net.Listen("tcp", ":8080")
    
    	if err != nil {
    		panic(err)
    	}
    } else {
    	// 新fork出来的，当前端口已被监听
    	l = fd
    	// 发送quit给父进程
    	killParent()
    	time.Sleep(time.Second)
    }
    
    // 启动server监听
    s := &http.Server{}
    	http.HandleFunc("/", func(rw http.ResponseWriter, r *http.Request) {
    		log.Printf("New request! From: %d, path: %s, method: %s: ", os.Getpid(),
    			r.URL, r.Method)
    	})
    go s.Serve(l)
    
    // 监听信号量
	upgradeLoop(&l, s)
}