Question

在一个值为 nil 的 channel 上发送和接收数据将永久阻塞：

func main() {
    var ch chan int // 未初始化，值为 nil
    for i := 0; i < 3; i++ {
        go func(i int) {
            ch <- i
        }(i)
    }

    fmt.Println("Result: ", <-ch)
    time.Sleep(2 * time.Second)
}

runtime 死锁错误：

fatal error: all goroutines are asleep - deadlock!

goroutine 1 [chan receive (nil chan)]

利用这个死锁的特性，可以用在 select 中动态的打开和关闭 case 语句块：

func main() {
    inCh := make(chan int)
    outCh := make(chan int)

    go func() {
        var in <-chan int = inCh
        var out chan<- int
        var val int

        for {
            select {
            case out <- val:
                println("--------")
                out = nil
                in = inCh
            case val = <-in:
                println("++++++++++")
                out = outCh
                in = nil
            }
        }
    }()

    go func() {
        for r := range outCh {
            fmt.Println("Result: ", r)
        }
    }()

    time.Sleep(0)
    inCh <- 1
    inCh <- 2
    time.Sleep(3 * time.Second)
}

运行效果：