go - Channel中的一个数据被两个routine接收

Question

你好，我学习了围棋例程和 channel 。 我用 channel 做了一些实验，我通过 channel 发送数据并尝试在 2 个函数中捕获它。但是我的第二个函数没有运行

这是我的代码:

package main

import (
    "fmt"
    "os"
    "time"
)

func timeout(duration int, ch chan<- bool) {
    time.AfterFunc(time.Duration(duration)*time.Second, func() {
        ch <- true
    })
}

func watcher(duration int, ch <-chan bool) {
    <-ch
    fmt.Println("\nTimeout! no Answer after", duration, "seconds")
    os.Exit(0)
}

func watcher2(duration int, ch <-chan bool) {
    <-ch
    fmt.Println("This is watcher 2 as a second receiver")
}

func main() {
    var data = make(chan bool)
    var duration = 5

    go timeout(duration, data)
    go watcher(duration, data)
    go watcher2(duration, data)

    var input string
    fmt.Print("What is 725/25 ? ")
    fmt.Scan(&input)

    if input == "29" {
        fmt.Println("Correct")
    } else {
        fmt.Println("Wrong!")
    }
}

你能告诉我一些关于它的解释吗？ 谢谢

Answer 1

正如@Andy Schweig 提到的，您只能从 Go channel 中拉取一次。如果你还想接收消息两次，你可以使用观察者设计模式:

import "fmt"

type Observer interface {
    Notify(message string)
}

type Watcher struct {
    name string
}

func (w Watcher) Notify(message string) {
    fmt.Printf("Watcher %s got message %s\n", w.name, message)
}

var watchers =  [...]Watcher {{name: "Watcher 1"}, {name: "Watcher 2"}}
var c = make(chan string)

func notifier() {

    var message string
    for {
        // Messaged pulled only once
        message = <- c

        // But all watchers still receive it
        for _, w := range watchers {
            w.Notify(message)
        }
    }
}

func main() {
    go notifier()

    c <- "hello"
    c <- "how are you?"
}