怎么设置 http 请求 并发 连接数 限制

package main


import (

    "flag"

    "fmt"

    "io/ioutil"

    "net/http"

    "os"

    "strconv"

    "time"

)


var ns = flag.String("n", "", "-n 100 | -n 1000 | ...")

var cs = flag.String("c", "", "-c 10 | -c 100 | ...")

var url = flag.String("url", "", "-url http://localhost:8080/")

var ps = flag.String("p", "", "true|false")


func main() {

    flag.Parse()


    n, err := strconv.Atoi(*ns)

    if err != nil {

        fmt.Println("cant parse n", err, *ns)

        os.Exit(1)

    }

    c, err := strconv.Atoi(*cs)

    if err != nil {

        fmt.Println("cant parse c", err, *cs)

        os.Exit(1)

    }

    if *url == "" {

        fmt.Println("please input url")

        os.Exit(1)

    }

    fmt.Println(n, c, *url)


    tasks := make(chan bool, n)

    for i := 0; i < n; i++ {

        tasks <- true

    }


    begin := time.Now()

    cnt := 0

    cntChan := make(chan bool)


    for i := 0; i < c; i++ {

        go func() {

            for len(tasks) > 0 {

                <-tasks

                res, err := http.Get(*url)

                if err != nil {

                    panic(err)

                } else {

                    defer res.Body.Close()

                    content, err := ioutil.ReadAll(res.Body)

                    if err != nil {

                        panic(err)

                    } else {

                        if *ps == "true" {

                            fmt.Println(string(content))

                        }

                    }

                }


                cntChan <- true

            }

        }()

    }


    for {

        b := false

        select {

        case <-cntChan:

            cnt += 1

            if cnt%(n/10) == 0 {

                b = true

                fmt.Printf("finished %d request \n", cnt)

            }

            if cnt == n {

                if !b {

                    fmt.Printf("finished %d request \n", cnt)

                }

                goto END

            }

        }

    }


END:

    ts := time.Now().Sub(begin).Seconds()

    fmt.Printf("%.3f requests/second \n", float64(cnt)/ts)

}