rest - 如何使用 Mutex 字段创建结构的元素

Question

我有一个 Get()功能:

func Get(url string) *Response {
    res, err := http.Get(url)
    if err != nil {
        return &Response{}
    }
    // res.Body != nil when err == nil
    defer res.Body.Close()
    body, err := ioutil.ReadAll(res.Body)
    if err != nil {
        log.Fatalf("ReadAll: %v", err)
    }
    reflect.TypeOf(body)
    return &Response{sync.Mutex(),string(body), res.StatusCode}
}

以及 Read()功能:

func Read(url string, timeout time.Duration) (res *Response) { 
    done := make(chan bool) 

    go func() {
        res = Get(url)      
        done <- true        
    }()     
        select {    // As soon as either
    case <-done:    // done is sent on the channel or 
    case <-time.After(timeout): // timeout
        res = &Response{"Gateway timeout\n", 504}

    }
    return
}

Response函数返回的类型定义为:

type Response struct {
    Body       string
    StatusCode int
}

这个读取函数使用了 Get()功能，还实现了超时。问题是如果发生超时并且 Get() 可能会发生数据竞争。响应写入 res同时在Read() .

我有一个解决这个问题的计划。就是用Mutex。为此，我将向 Response 添加一个字段结构:

type Response struct {
    mu         sync.Mutex
    Body       string
    StatusCode int
}

这样 Response可以上锁。但是，我不确定如何在代码的其他部分修复此问题。

对于 Get()，我的尝试看起来像这样:

func Get(url string) *Response {
    res, err := http.Get(url)
    if err != nil {
        return &Response{}
    }
    // res.Body != nil when err == nil
    defer res.Body.Close()
    body, err := ioutil.ReadAll(res.Body)
    if err != nil {
        log.Fatalf("ReadAll: %v", err)
    }
    reflect.TypeOf(body)
    return &Response{sync.Mutex(),string(body), res.StatusCode} // This line is changed.
}

对于 Read() :

func Read(url string, timeout time.Duration) (res *Response) { 
    done := make(chan bool) 
    res = &Response{sync.Mutex()} // this line has been added

    go func() { 
        res = Get(url)      
        done <- true        
    }()     
        select {    
    case <-done:    
    case <-time.After(timeout):
        res.mu.Lock()
        res = &Response{sync.Mutex(), "Gateway timeout\n", 504} // And mutex was added here.

    }
    defer res.mu.Unlock()
    return
}

这个“解决方案”产生了这些错误:

./client.go:54: missing argument to conversion to sync.Mutex: sync.Mutex()
./client.go:63: missing argument to conversion to sync.Mutex: sync.Mutex()
./client.go:63: too few values in struct initializer
./client.go:73: missing argument to conversion to sync.Mutex: sync.Mutex()
./client.go:95: cannot use "Service unavailable\n" (type string) as type sync.Mutex in field value
./client.go:95: cannot use 503 (type int) as type string in field value
./client.go:95: too few values in struct initializer

在这种情况下使用 Mutex 的正确方法是什么？

Answer 1

虽然您对 Volker 指导的回答很好，但您可能需要考虑使用非默认的 http.Client，以便您可以在客户端上设置 Timeout请求(这样您就不必担心自己处理超时)。