为什么这些Golang代码无法在多个时间中选择。

Question

Why doesn't this Golang code to select among multiple time.After channels work?

See code below. The 'timeout' message is never issued. Why?

package main

import (
    "fmt"
    "time"
)

func main() {
    count := 0
    for {
        select {
        case <-time.After(1 * time.Second):
            count++
            fmt.Printf("tick %d
", count)
            if count >= 5 {
                fmt.Printf("ugh
")
                return
            }
        case <-time.After(3 * time.Second):
            fmt.Printf("timeout
")
            return
        }
    }
}

Run it on Playground: http://play.golang.org/p/1gku-CWVAh

Output:

tick 1
tick 2
tick 3
tick 4
tick 5
ugh

Answer 1

Because time.After is a function, so on every iteration it returns a new channel. If you want this channel to be the same for all iterations, you should save it before the loop:

timeout := time.After(3 * time.Second)
for {
    select {
    //...
    case <-timeout:
        fmt.Printf("timeout
")
        return
    }
}

Playground: http://play.golang.org/p/muWLgTxpNf.