Select from slice of channels(sending to a free channel)?

Question

I'm making multiples http request:

    type item struct{
       me []byte
    }
    items := getItems()
    for _, me := range items {
          me.save()
    }

In order to do it efficiently I'm doing it with go rutines, my first approach was to make it like a pool of go rutines:

    items := getItems()
    var wg sync.WaitGroup
    wg.Add(len(items))
    for _, me := range items {
        go func(me item) {
            me.save()
            wg.Done()
        }(me)
    }
    wg.Wait()

But they all try to make http request at the same time and some of them fail because of my bandwidth can't handle them all. So I try channels along with select instead :

    channel1 := make(chan item)
    channel2 := make(chan item)
    channel3 := make(chan item)
    var wg sync.WaitGroup
    items := getItems()
    wg.Add(len(items))
    go func() {
        for me := range channel1 {
            me.save()
            wg.Done()
        }
    }()
    go func() {
        for me := range channel2 {
            me.save()
            wg.Done()
        }
    }()
    go func() {
        for me := range channel3 {
            me.save()
            wg.Done()
        }
    }()
    for _, me := range items {
        select {
        case channel1 <- me:
        case channel2 <- me:
        case channel3 <- me:
        }
    }

But adding more go rutines to find the max go rutines my bandwidht can handle, my code gets larger and larger, and I try to do this:

    max:=7
    var channels []chan item
    for i:=0;i<max;i++{
        channel=make(chan item)
        channels=append(channels,channel)
    }
    for _, me := range items {
        select {
            //???????????????
        }
    }

but I'm not prety sure how to do it as the last approach

Also take in mind that "Select from slice of channels" was a question already asked, but their answers were only when select is listening which channel arrive first, in my case I want Select to send any free channel, so it's different

Answer 1

I had a wrong approach and the answer was easy with worker pools

type item struct {
    me []byte
}

func worker(canalFiles <-chan item, wg *sync.WaitGroup) {
    for file := range canalFiles {
        file.save()
        wg.Done()
    }
}
func main() {
    var wg sync.WaitGroup
    items := getItems()
    wg.Add(len(items))
    canalFiles := make(chan item)
    for i := 0; i < 8; i++ {
        go worker(canalFiles, &wg)
    }
    for _, file := range items {
        canalFiles <- file
    }
    fmt.Printf("waiting.....")
    wg.Wait()
}

Answer 2

You can use reflect.Select, creating a slice of SelectCase structs with Dir=SelectSend, like this:

max:=7
var channels []chan item
for i:=0;i<max;i++{
    channel=make(chan item)
    channels=append(channels,channel)
}
for _, me := range items {
    cases := make([]reflect.SelectCase, max)
    for j := 0; j < max; j++ {
        cases[j] = reflect.SelectCase{
            Dir: reflect.SelectSend,
            Chan: reflect.ValueOf(channels[j]),
            Send: reflect.ValueOf(me)
        }
    }
    reflect.Select(cases)
}