类似 pthread_cond_broadcast() 的功能。利用从已关闭的 channel 读取数据时总是非阻塞的特性，可以实现在一个协程中向其他多个协程广播某个事件发生的通知：

package main

import (
    "fmt"
    "time"
)

func main() {
    N := 10
    exit := make(chan struct{})
    done := make(chan struct{}, N)

    //start N worker goroutines
    for i := 0; i < N; i++ {
        go func(n int) {
            for {
                select {
                // wait for exit signal
                case <-exit:
                    fmt.Printf("worker goroutine #%d exit\n", n)
                    done <- struct{}{}
                    return
                case <-time.After(time.Second):
                    fmt.Printf("worker goroutine #%d is working...\n", n)
                }
            }
        }(i)
    }

    time.Sleep(3 * time.Second)
    //broadcast exit signal
    close(exit)

    //wait for all worker goroutines exit
    for i := 0; i < N; i++ {
        <-done
    }

    fmt.Println("main goroutine exit")
}

/*
输出结果：
worker goroutine #0 is working...
worker goroutine #2 is working...
worker goroutine #3 is working...
worker goroutine #1 is working...
worker goroutine #4 is working...
worker goroutine #8 is working...
worker goroutine #9 is working...
worker goroutine #7 is working...
worker goroutine #6 is working...
worker goroutine #5 is working...
worker goroutine #3 is working...
worker goroutine #2 is working...
worker goroutine #0 is working...
worker goroutine #5 is working...
worker goroutine #6 is working...
worker goroutine #8 is working...
worker goroutine #9 is working...
worker goroutine #4 is working...
worker goroutine #1 is working...
worker goroutine #7 is working...
worker goroutine #3 exit
worker goroutine #8 exit
worker goroutine #7 exit
worker goroutine #1 exit
worker goroutine #9 exit
worker goroutine #5 exit
worker goroutine #6 exit
worker goroutine #0 exit
worker goroutine #2 exit
worker goroutine #4 exit
main goroutine exit

 */