执行例程：发出并发API请求

Question

I am trying to understand channels and goroutines and tried to write a goroutine for making concurrent API requests to the server

But when I am running the code using a goroutine, it seems like it is taking the same time as it does without a goroutine.

func sendUser(user string, ch chan<- string)  {
    resp,err := http.get("URL"/user)
    //do the processing and get resp=string
    ch <- resp
}


func AsyncHTTP(users []string) ([]string, error) {
    ch := make(chan string)
    var responses []string
    var user string

    for _ , user = range users {
        go sendUser(user, ch)

        for {
            select {
            case r := <-ch:
                if r.err != nil {
                    fmt.Println(r.err)
                }
                responses = append(responses, r)
                **//Is there a better way to show that the processing of response is complete**?
                if len(responses) == len(users) { 
                    return responses, nil
                }
            case <-time.After(50 * time.Millisecond):
                fmt.Printf(".")
            }
        }
    }
    return responses, nil
}

Questions:

1. Even though I am using a goroutine, request completion time is same as it is without goroutines? Is there anything I am doing wrong with goroutines?

2. For telling the job not to wait anymore here I am using:

   if len(responses) == len(users)
   

   Is there a better way to show that the processing of response is complete and tell ch not to wait anymore?

3. What is wait.Syncgroup? How can I use it in my goroutine?

Answer 1

I might do something like this..

func sendUser(user string, ch chan<- string, wg *sync.WaitGroup) {
    defer wg.Done()
    resp, err := http.Get("URL/" + user)
    if err != nil {
        log.Println("err handle it")
    }
    defer resp.Body.Close()
    b, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Println("err handle it")
    }
    ch <- string(b)
}

func AsyncHTTP(users []string) ([]string, error) {
    ch := make(chan string)
    var responses []string
    var user string
    var wg sync.WaitGroup
    for _, user = range users {
        wg.Add(1)
        go sendUser(user, ch, &wg)
    }

    // close the channel in the background
    go func() {
        wg.Wait()
        close(ch)
    }()
    // read from channel as they come in until its closed
    for res := range ch {
        responses = append(responses, res)
    }

    return responses, nil
}

It allows to read from the channel as they are sent. By using a waitgroup I'll know when to close the channel. By putting the waitgroup and close in a goroutine I can read from the channel in "realtime" without blocking.