如何在golang中使用atomic的Load和Store

Question

下面是使用atomic.Value测试结构B的读写互访的一段代码，但我遇到了一些错误，指示无效指针访问。所以我该怎么做？这样做的惯用语是什么？

type A struct {
    numMap map[string]int
}

type B struct {
    numMap map[string]*A
}

var store atomic.Value

var chanA chan bool = make(chan bool, 100)
var chanB chan bool = make(chan bool, 100)

var b *B = &B{}

func fetchB() {
    for i := 0; i < 10000; i++ {
        c := store.Load().(B)
        for k, v := range c.numMap {
            fmt.Println(k, v)
            for k2, v2 := range v.numMap {
                fmt.Println(k2, v2)
            }
        }
    }
    chanA <- true
}

func writeB() {
    for i := 0; i < 10000; i++ {
        //b := store.Load().(B)
        a := new(A)
        a.numMap = make(map[string]int)
        a.numMap["AMap"] = i
        b.numMap = make(map[string]*A)
        b.numMap["str"] = a
        b.numMap["strA"] = a
        delete(b.numMap, "str")
        delete(b.numMap["strA"].numMap, "AMap")
        store.Store(b)
    }
    chanB <- true
}
func main() {
    store.Store(*b)
    for i := 0; i < 100; i++ {
        go writeB()
        go fetchB()
    }
    for i := 0; i < 100; i++ {
        <-chanA
        <-chanB
    }
}

很抱歉，我在问题的第一个 post 中遗漏了一些内容。如果我评论 b := store.Load().(B) 错误会出现，如果我让它可见，它就会消失。那为什么会这样呢？

我得到的错误是这样的：

panic: sync/atomic: store of inconsistently typed value into Value

goroutine 5 [running]: sync/atomic.(*Value).Store(0x597310, 0x4b7f40, 0x597198)
    /usr/local/go/src/sync/atomic/value.go:76 +0x1e9 main.writeB()
    /home/bzhang/devCode/common/src/go/src/audience_service/test.go:47 +0x2cc created by main.main
    /home/bzhang/devCode/common/src/go/src/audience_service/test.go:54 +0x71

goroutine 1 [chan receive]: main.main()
    /home/bzhang/devCode/common/src/go/src/audience_service/test.go:59 +0xf3

goroutine 6 [runnable]: main.fetchB()
    /home/bzhang/devCode/common/src/go/src/audience_service/test.go:23 created by main.main
    /home/bzhang/devCode/common/src/go/src/audience_service/test.go:55 +0x89

goroutine 7 [runnable]: main.writeB()
    /home/bzhang/devCode/common/src/go/src/audience_service/test.go:36 created by main.main
    /home/bzhang/devCode/common/src/go/src/audience_service/test.go:54 +0x71

goroutine 8 [runnable]: main.fetchB()
    /home/bzhang/devCode/common/src/go/src/audience_service/test.go:23 created by main.main
    /home/bzhang/devCode/common/src/go/src/audience_service/test.go:55 +0x89

goroutine 9 [runnable]: main.writeB()
    /home/bzhang/devCode/common/src/go/src/audience_service/test.go:36 created by main.main
    /home/bzhang/devCode/common/src/go/src/audience_service/test.go:54 +0x7

Answer 1

当您注释掉 b := store.Load().(B) 时，函数中使用的变量 b 是 *B 类型的全局 b 并且当您执行 store.Store(b) 你得到错误是因为你试图在存储中存储 *B 类型的值，该值的类型为 B。这就是错误谈论不一致类型的原因。您可以将 store.Store(b) 更改为 store.Store(*b)，代码将正常运行。

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