golang中Map的并发写入

原理

golang中的map不是线程安全的，所以在并发的情况下不能直接使用map。

反面例子

package main

import (
    "strconv"
    "time"
)

var m = make(map[string]interface{})

func main() {
    testMap(m)
    time.Sleep(2 * time.Second)
}

func testMap() {
    go func() {
        for i := 0; i < 10; i++ {
            name := "WangWu" + strconv.Itoa(i)
            writeMap(m, name, i)
        }
    }()

    go func() {
        for i := 0; i < 10; i++ {
            name := "ZhuoQi" + strconv.Itoa(i)
            writeMap(m, name, i)
        }
    }()
}

func writeMap(m map[string]int, key string, val int) {
    m[key] = val
}

运行时，会报错：

fatal error: concurrent map writes

解决办法

1. Map加锁

package main

import (
    "fmt"
    "strconv"
    "sync"
    "time"
)

// 定义锁
var locker = &sync.RWMutex{}
var m = make(map[string]interface{})

func main() {
    testMap()
    time.Sleep(2 * time.Second)
    fmt.Println(m)
}

func testMap() {
    go func() {
        for i := 0; i < 10; i++ {
            name := "WangWu" + strconv.Itoa(i)
            writeMap(name, i)
        }
    }()

    go func() {
        for i := 0; i < 10; i++ {
            name := "ZhuoQi" + strconv.Itoa(i)
            writeMap(name, i)
        }
    }()
}

func writeMap(key string, val int) {
    locker.Lock()
    m[key] = val
    locker.Unlock()
}

2. 使用sync.Map

package main

import (
    "fmt"
    "strconv"
    "sync"
    "time"
)

var m = sync.Map{}

func main() {
    testMap()
    time.Sleep(2 * time.Second)
    m.Range(func(k, v interface{}) bool {
        fmt.Println("map:", k, v)
        return true
    })
}

func testMap() {
    go func() {
        for i := 0; i < 10; i++ {
            name := "WangWu" + strconv.Itoa(i)
            m.Store(name, i)
        }
    }()

    go func() {
        for i := 0; i < 10; i++ {
            name := "ZhuoQi" + strconv.Itoa(i)
            m.Store(name, i)
        }
    }()
}