根据控制通道的缓存大小来控制并发的goroutine的最大数目 ```go package main import ( "fmt" "sync" "time" ) func main() { var wg sync.WaitGroup var limit = make(chan int, 3) var works []func() for i := 0; i < 100; i++ { works = append(works, func() { fmt.Println("hi") }) } for _, w := range works { work := w wg.Add(1) go func() { defer wg.Done() limit <- 1 work() time.Sleep(time.Second) <-limit }() } wg.Wait() } ```