并发注意事项

go func()

func worker(cannel chan struct{}) {
	for {
		select {
		default:
			fmt.Println("hello")
			time.Sleep(100 * time.Millisecond)
		case <-cannel:
			// 退出
		}
	}
}

func CancelWithChannel() {
	cannel := make(chan struct{})
	go worker(cannel)

	time.Sleep(time.Second)
	cannel <- struct{}{}
}

func workerv2(wg *sync.WaitGroup, cancel chan bool) {
	defer wg.Done()

	for {
		select {
		default:
			fmt.Println("hello")
			time.Sleep(100 * time.Millisecond)
		case <-cancel:
			return
		}
	}
}

func CancelWithDown() {
	cancel := make(chan bool)

	var wg sync.WaitGroup
	for i := 0; i < 10; i++ {
		wg.Add(1)
		go workerv2(&wg, cancel)
	}

	time.Sleep(time.Second)

	// 发送退出信号
	close(cancel)

	// 等待goroutine 安全退出
	wg.Wait()
}

func workerV3(ctx context.Context, wg *sync.WaitGroup) error {
	defer wg.Done()

	for {
		select {
		default:
			fmt.Println("hello")
			time.Sleep(100 * time.Millisecond)
		case <-ctx.Done():
			return ctx.Err()
		}
	}
}
func CancelWithCtx() {
	// 控制超时
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)

	var wg sync.WaitGroup
	for i := 0; i < 10; i++ {
		wg.Add(1)
		go workerV3(ctx, &wg)
	}

	time.Sleep(time.Second)

	// 取出任务
	cancel()

	// 等待安全退出
	wg.Wait()
}

func DealPanic() {
	defer func() {
		if err := recover(); err != nil {
			fmt.Println(err)
		}
	}()

	arr := []int{0}
	_ = arr[2]
}

// 输出: runtime error: index out of range [2] with length 1

func DealPanicInG() {
	defer func() {
		if err := recover(); err != nil {
			fmt.Println(err)
		}
	}()

	wg.Add(1)
	go work()

	wg.Wait()
}

func work() {
	arr := []int{0}
	_ = arr[2]
	wg.Done()
}

// Serve a new connection.
func (c *conn) serve(ctx context.Context) {
	c.remoteAddr = c.rwc.RemoteAddr().String()
	ctx = context.WithValue(ctx, LocalAddrContextKey, c.rwc.LocalAddr())
	defer func() {
		if err := recover(); err != nil && err != ErrAbortHandler {
			const size = 64 << 10
			buf := make([]byte, size)
			buf = buf[:runtime.Stack(buf, false)]
			c.server.logf("http: panic serving %v: %v\n%s", c.remoteAddr, err, buf)
		}
		if !c.hijacked() {
			c.close()
			c.setState(c.rwc, StateClosed, runHooks)
		}
	}()

func DealPanicInGV2() {
	// 处理主Goroutine的异常
	defer func() {
		if err := recover(); err != nil {
			fmt.Println(err)
		}
	}()

	wg.Add(1)
	go workV2()

	wg.Wait()
}

func workV2() {
	// 处理协程的异常
	defer func() {
		wg.Done()

		if err := recover(); err != nil {
			fmt.Println(err)
		}
	}()

	arr := []int{0}
	_ = arr[2]
}

type SiteRespCallBack func(SiteResp)

// 构造请求
func doSiteRequest(cb SiteRespCallBack, url string) {
	res := SiteResp{}
	startAt := time.Now()
	defer func() {
		res.Cost = time.Since(startAt).Milliseconds()
		cb(res)
		wg.Done()
	}()

	resp, err := client.Get(url)
	if resp != nil {
		res.Status = resp.StatusCode
	}
	if err != nil {
		res.Err = err
		return
	}

	// 站不处理结果
	_, err = ioutil.ReadAll(resp.Body)
	defer resp.Body.Close()
	if err != nil {
		res.Err = err
		return
	}

	// res.Resp = string(byt)
}

func CallBackMode() {
	endpoints := []string{
		"https://www.baidu.com",
		"https://segmentfault.com/",
		"https://blog.csdn.net/",
		"https://www.jd.com/",
	}

	// 一个endpoints返回一个结果, 缓冲可以确定
	respChan := make(chan SiteResp, len(endpoints))
	defer close(respChan)

	ret := make([]SiteResp, 0, len(endpoints))
	cb := func(resp SiteResp) {
		ret = append(ret, resp)
	}

	// 并行爬取
	for _, endpoints := range endpoints {
		wg.Add(1)
		go doSiteRequest(cb, endpoints)
	}

	// 等待结束
	wg.Wait()

	for _, v := range ret {
		fmt.Println(v)
	}
}

func TestMap(t *testing.T) {
	list := []string{"abc", "def", "fqp"}
	out := MapStrToUpper(list, func(item string) string {
		return strings.ToUpper(item)
	})
	fmt.Println(out)
}

func MapStrToUpper(data []string, fn func(string) string) []string {
	newData := make([]string, 0, len(data))
	for _, v := range data {
		newData = append(newData, fn(v))
	}

	return newData
}