大家来解惑--这段代码有啥问题？

``` package main import ( "fmt" "time" ) func main() { limiter := make(chan bool, 10) for i := 0; i < 100; i++ { limiter <- true go download(i, limiter) } } func download(index int, limiter chan bool) { time.Sleep(1 * time.Second) fmt.Println("start to download :", index) <-limiter } ``` 上面这段代码执行结果为什么最大打印值直到 89 ？ 当把 ``` time.Sleep(1 * time.Second) fmt.Println("start to download :", index) ``` 两行上下调换之后，变成以下的代码： ``` fmt.Println("start to download :", index) time.Sleep(1 * time.Second) ``` 就能正常打印到 99 了？