Golang通道:超时模式不适用于示例

Timeout pattern 为了我的项目。以下是上述链接的示例代码:

c1 := make(chan string, 1)
go func() {
    time.Sleep(2 * time.Second)
    c1 <- "result 1"
}()

select {
case res := <-c1:
    fmt.Println(res)
case <-time.After(1 * time.Second):
    fmt.Println("timeout 1")
}

另一个例子是:

c2 := make(chan string, 1)
    go func() {
        time.Sleep(2 * time.Second)
        c2 <- "result 2"
    }()
    select {
    case res := <-c2:
        fmt.Println(res)
    case <-time.After(3 * time.Second):
        fmt.Println("timeout 2")
    }

for {
    select {
    case ev := <-c.EventChannel():
        // do something here
    case <-time.After(2 * time.Second):
        // this condition never happend
        return
    default:
       // do nothing as non-blocking channel pattern
    }
}

但我不知道为什么代码永远不会遇到超时情况。当我搬家的时候 time.After(2 * time.Second) 在单独的语句中,它是有效的。以下是修改后的代码:

timeout := time.After(2 * time.Second)
for {
    select {
    case ev := <-c.EventChannel():
        // do something here
    case <-timeout:
        require.Equal(t, "time out after 2s", "")
    default:
        // do nothing as non-blocking channel pattern
    }
}