當(dāng)我運(yùn)行此代碼時(shí)，我不明白為什么在打印X后它不打印其他情況。我希望我應(yīng)該看到X打印出來三秒鐘，然后最后從server2package mainfunc server1(ch chan string) {    time.Sleep(6 * time.Second)    ch <- "from server1"}func server2(ch chan string) {    time.Sleep(3 * time.Second)    ch <- "from server2"}func main() {    output1 := make(chan string)    output2 := make(chan string)    go server1(output1)    go server2(output2)    select {    case s1 := <-output1:        fmt.Println(s1)    case s2 := <-output2:        fmt.Println(s2)    default:        fmt.Println(“X”)    }}