Golang select语句退出循环

package main

import (
    "fmt"
    "time"
)

func main() {
    done := make(chan interface{})
    go func() {
        time.Sleep(5 * time.Second)
        close(done)
    }()

    workCounter := 0
loop:
    for {
        select {
        case <-done:
            break loop
        default:
        }
        workCounter++
        time.Sleep(1 * time.Second)
    }

    fmt.Printf("Achieved %v cycles of work before signaled to stop.\n", workCounter)
}