为什么我的Golang压力测量工具和Apache Batch生成不同数量的ESTABLISHED链接？

Question

Apache Batch is a popular pressure measuring tool.

I write a tool with the same function in golang myself. Then I make some tests. I find it works well.

But accidentally, I find a difference from my tool and Apache Batch:

When checking ESTABLISHED link number by the cmd netstat -na|grep ESTABLISHED|wc -l:

Use cmd ab -n 128000 -c 128 http://127.0.0.1:8000/, the cmd above returns a number near 128.

But use my own tool, the cmd returns near 256 (when set concurrency 128).

Why my own tool have twice the expected number of concurrencies?

My code:

func request(cli *http.Client, uri string) {
    resp, err := cli.Get(uri)
    if err != nil {
        panic(err)
    }
    defer resp.Body.Close()
    if resp.StatusCode != 200 {
        panic("return" + strconv.Itoa(resp.StatusCode))
    }
}

func workRoutine(ch chan string, wg *sync.WaitGroup) {
    cli := &http.Client{}
    for uri := range ch {
        request(cli, uri)
    }
    wg.Done()
}

func main() {
    rnum := 128
    tnum := 128000

    url := "http://127.0.0.1:8000/"

    ch := make(chan string)
    var wg sync.WaitGroup

    go func() {
        for i := 0; i < tnum; i++ {
            ch <- url
        }
        close(ch)
    }()

    wg.Add(rnum)
    for i := 0; i < rnum; i++ {
        go workRoutine(ch, &wg)
    }

    stime := time.Now()
    wg.Wait()
    dtime := time.Now().Sub(stime)
    fmt.Println("Timecost", dtime)
    fmt.Println("Throughputs", float64(tnum)/dtime.Seconds())
}