when lots of io requset running，the other requests will wait

[meiyang1123]

• go version: go1.12.2
• gin version (or commit ref):
• operating system: windows/amd64

Description

A Testing
run gin server with code

func main() {
	gin.SetMode(gin.ReleaseMode)
	r := gin.New()
	r.GET("/ping", func(c *gin.Context) {
		c.JSON(200, gin.H{"message": "ping"})
	})
	r.GET("/wait10s", func(c *gin.Context) {
		time.Sleep(time.Second * 10)
		c.JSON(200, gin.H{"message": " 10s"})
	})
	r.GET("/download", func(c *gin.Context) {
               // a 5.85Mb file
		c.File(`D:\Project\awesomeProject\asset\SyncBaseInfo_1552615252.zip`)
	})
	r.Run() // listen and serve on 0.0.0.0:8080
}

and then request to the server with code

// requset.go
func get(url string, d time.Duration) {
	start := time.Now()
	resp, err := http.Get(url)
	if err != nil {
		fmt.Println(err.Error())
	} 
	defer resp.Body.Close()
	_, err = ioutil.ReadAll(resp.Body)
	if err != nil {
		fmt.Println(err.Error())
	}
	d2 := time.Now().Sub(start)
	if d2 > d {
		fmt.Println(url, d2)
	}
}

func main() {
	sysGroup := sync.WaitGroup{}
	for i := 10; i < 50; i++ {
		go func() {
			sysGroup.Add(1)
			get("http://localhost:8080/wait10s", time.Millisecond*1000)
			sysGroup.Done()
		}()
	}

	for i := 0; i < 100; i++ {
		go func() {
			sysGroup.Add(1)
			get("http://localhost:8080/download", time.Millisecond*50)
			sysGroup.Done()
		}()

	}
	time.Sleep(time.Millisecond * 20)
	for i := 0; i < 100; i++ {
		go func() {
			sysGroup.Add(1)
			get("http://localhost:8080/ping", time.Millisecond*1)
			sysGroup.Done()
		}()
	}
	sysGroup.Wait()
}

when request.go run at first time,ping request will back before download request,when request.go run again,ping request will back after download .

Run server with go http ，the problem does not appear。

// run with package http
func IndexHandler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintln(w, "hello world")
}

func waitHandler(w http.ResponseWriter, r *http.Request) {
	time.Sleep(time.Second * 10)
	fmt.Fprintln(w, "hello world")
}
func DownHandler(writer http.ResponseWriter, request *http.Request) {
	reader, err := os.Open(`D:\Project\awesomeProject\asset\SyncBaseInfo_1552615252.zip`)
	if err != nil || reader == nil {
		writer.Write([]byte("error !!"))
		return
	}
	defer reader.Close()
	http.ServeContent(writer, request, "heeh", time.Now(), reader)

}
func listenSignal() {
	sigs := make(chan os.Signal, 1)
	signal.Notify(sigs, syscall.SIGHUP, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT)
	select {
	case <-sigs:
		fmt.Println("exitapp,sigs:", sigs)
		os.Exit(0)
	}
}
func main() {
	go func() {
		http.HandleFunc("/ping", IndexHandler)

		http.HandleFunc("/download", DownHandler)
		http.HandleFunc("/wait10s", waitHandler)
		http.ListenAndServe("0.0.0.0:8080", nil)
		fmt.Println(222222222222222)
	}()

	listenSignal()
}

[thinkerou]

@meiyang1123 please update your example, please see https://github.com/golang/go/blob/master/src/sync/example_test.go#L29, thanks!
please update and check, or else reopen.
now closing. thanks!

[meiyang1123]

I update and check again, got the same result。

import (
	"fmt"
	"io/ioutil"
	"net/http"
	"sync"
	"time"
)

func get(url string) {
	start := time.Now()
	resp, err := http.Get(url)
	if err != nil {
		fmt.Println(err.Error())
	}
	defer resp.Body.Close()
	_, err = ioutil.ReadAll(resp.Body)
	if err != nil {
		fmt.Println(err.Error())
	}
	d2 := time.Now().Sub(start)
	fmt.Println(url, d2)

}

func main() {
	sysGroup := sync.WaitGroup{}
	var urls = []string{
		"http://localhost:8080/wait10s",
		"http://localhost:8080/download",
		"http://localhost:8080/ping",
	}
	for i := 0; i < 50; i++ {
		for _, url := range urls {
			sysGroup.Add(1)
			go func(url string) {
				defer sysGroup.Done()
				get(url)
			}(url)
		}

	}
	sysGroup.Wait()
}

Result：

I hope you can help me.