doumen1883 2014-04-17 16:32
浏览 322
已采纳

如何从Go中的匿名函数访问全局变量?

I have a code:

var test string

func main() {
    http.HandleFunc("/", func(writer http.ResponseWriter, request *http.Request) {
        test = "index"
    })

    fmt.Println(test)

    if error := http.ListenAndServe(":9001", nil); error != nil {
        log.Fatal("Error!", error)
    }
}

How to change the value of the test variable in the anonymous function? I will be thankful!

  • 写回答

1条回答 默认 最新

  • douxiuyi6529 2014-04-17 16:49
    关注

    The HTTP handler does change your global variable; however you don't protect access to the global variable and thus have a race condition. That is to say fmt.Println(test) runs before your http.HandleFunc.

    I'm assuming this is a toy example: If you want to change your code to wait for the value to be changed / wait for an HTTP hit, before terminating, then you could do this:

    var test string
    var doneCh = make(chan bool, 1)
    
    func main() {
        http.HandleFunc("/", func(writer http.ResponseWriter, request *http.Request) {
            test = "index"
            select {
            case doneCh <- true:
            default:
            }
        })
    
        go func() {
            <-doneCh
            fmt.Println(test)
        }()
    
        if error := http.ListenAndServe(":9001", nil); error != nil {
            log.Fatal("Error!", error)
        }
    }
    

    This uses a channel to guard the state of test. In real code it would be more likely to use sync.Once or sync.Mutex. Also, I should mention (and I hope you already realize) mutating global state is always something to be avoided when possible.

    本回答被题主选为最佳回答 , 对您是否有帮助呢?
    评论

报告相同问题?

悬赏问题

  • ¥15 用三极管设计—个共射极放大电路
  • ¥15 请完成下列相关问题!
  • ¥15 drone 推送镜像时候 purge: true 推送完毕后没有删除对应的镜像,手动拷贝到服务器执行结果正确在样才能让指令自动执行成功删除对应镜像,如何解决?
  • ¥15 求daily translation(DT)偏差订正方法的代码
  • ¥15 js调用html页面需要隐藏某个按钮
  • ¥15 ads仿真结果在圆图上是怎么读数的
  • ¥20 Cotex M3的调试和程序执行方式是什么样的?
  • ¥20 java项目连接sqlserver时报ssl相关错误
  • ¥15 一道python难题3
  • ¥15 牛顿斯科特系数表表示