解决资源共享时的冲突问题的方法

有一个测试服务有 2 个请求。这些请求使用 actualorders 变量形式的共享资源。假设正在运行数百个并行查询，则 actualorders 变量中可能会发生数据冲突。特别是当我循环遍历数组时。为了防止这种情况，使用 mutex 是否足够，就像我在下面的示例中所做的那样？

ma​​in.go：

package main

import (
    "encoding/json"
    "errors"
    "fmt"
    "net/http"
    "os"
    "time"
)

type Order struct {
    Room      string    `json:"room"`
    UserEmail string    `json:"email"`
    From      time.Time `json:"from"`
    To        time.Time `json:"to"`
}

var ActualOrders = []Order{}

var mutex sync.Mutex

func getOrders(responseWriter http.ResponseWriter, request *http.Request) {
    userEmail := request.URL.Query().Get("email")

    results := []Order{}

    mutex.Lock()

    for _, item := range ActualOrders {
        if item.UserEmail == userEmail {
            results = append(results, item)
        }
    }

    mutex.Unlock()

    bytes, err := json.Marshal(results)
    if err != nil {
        http.Error(responseWriter, err.Error(), http.StatusInternalServerError)
        return
    }

    responseWriter.Header().Set("Content-type", "application/json")
    responseWriter.WriteHeader(http.StatusOK)
    responseWriter.Write(bytes)
}

func createOrder(responseWriter http.ResponseWriter, request *http.Request) {
    var newOrder Order

    requestBody := request.Body
    defer request.Body.Close()
    err := json.NewDecoder(requestBody).Decode(&newOrder)
    if err != nil {
        http.Error(responseWriter, err.Error(), http.StatusBadRequest)
        return
    }

    mutex.Lock()

    for _, order := range ActualOrders {
        if !(newOrder.To.Before(order.From) || newOrder.From.After(order.To)) {
            http.Error(responseWriter, http.StatusText(http.StatusConflict), http.StatusConflict)
            return
        }
    }

    ActualOrders = append(ActualOrders, newOrder)

    mutex.Unlock()

    responseWriter.WriteHeader(http.StatusCreated)
}

func main() {
    mux := http.NewServeMux()

    mux.HandleFunc("/orders", getOrders)
    mux.HandleFunc("/order", createOrder)

    err := http.ListenAndServe(":8080", mux)
    if errors.Is(err, http.ErrServerClosed) {
        fmt.Printf("server closedn")
    } else if err != nil {
        fmt.Printf("error starting server: %sn", err)
        os.Exit(1)
    }
}

正确答案

像您一样使用互斥锁可以防止数据争用。不过，您的实施还可以改进。

您可以使用 rwmutex，对 getorders 函数使用读锁，对 createorder 函数使用锁。这将允许在写入时对 actualorders 变量进行独占访问，但允许共享读取：

var mutex sync.RWMutex

func getOrders(responseWriter http.ResponseWriter, request *http.Request) {
    ...
    mutex.RLock()
    ... 
    mutex.RUnlock()
}

func createOrder(responseWriter http.ResponseWriter, request *http.Request) {
    ...
    mutex.Lock()
    for _, order := range ActualOrders {
       ... 
    }
    ActualOrders = append(ActualOrders, newOrder)
    mutex.Unlock()

 }