Golang的map并发安全

已知多个goroutine同时读写Map会出问题
如下代码会抛出异常

package main
import (
    "time"
    "fmt"
)
func main()  {
    c := make(map[string]int)
    go func() {//开一个goroutine写map
        for j := 0; j < 1000000; j++ {
            c[fmt.Sprintf("%d", j)] = j
        }
    }()
    go func() {    //开一个goroutine读map
        for j := 0; j < 1000000; j++ {
            fmt.Println(c[fmt.Sprintf("%d",j)])
        }
    }()

    time.Sleep(time.Second*20)
}

运行结果

fatal error: concurrent map read and map write

由此可见golang中的map并不是并发安全的

那么同时进行len、encode、decode、或者同时write、read的操作呢?

以下进行测试

同时write和len(正常)

package main

import (
    "time"
    "fmt"
)

func main()  {
    c := make(map[string]int)
    go func() {//开一个goroutine写map
        for j := 0; j < 1000000; j++ {
            c[fmt.Sprintf("%d", j)] = j
        }
    }()
    go func() {    //开一个goroutine读map
        for j := 0; j < 1000000; j++ {
            //fmt.Println(c[fmt.Sprintf("%d",j)])
            fmt.Println(len(c))
        }
    }()

    time.Sleep(time.Second*20)
}

运行结果正常,当然,同时read和len也是ok的

同时write和json.Marshal(异常)

package main

import (
    "time"
    "fmt"
    "encoding/json"
)

func main()  {
    c := make(map[string]int)
    go func() {
        for j := 0; j < 1000000; j++ {
            c[fmt.Sprintf("%d", j)] = j
        }
    }()
    go func() {
        for j := 0; j < 1000000; j++ {
            json.Marshal(c)
        }
    }()
    time.Sleep(time.Second*20)
}

运行结果

fatal error: concurrent map iteration and map write

同时read和json.Unmarshal到同一个对象(异常)

package main

import (
    "time"
    "fmt"
    "encoding/json"
)

func main() {
    c := make(map[string]int)
    for j := 0; j < 100; j++ {
        c[fmt.Sprintf("%d", j)] = j
    }
    b1,_:=json.Marshal(c)
    c2 := make(map[string]int)
    go func() { //开一个goroutine读map
        for j := 0; j < 1000000; j++ {
            fmt.Println(c2[fmt.Sprintf("%d", j)])
        }
    }()
    go func() { //开一个goroutine读map
        for j := 0; j < 1000000; j++ {
            json.Unmarshal(b1,&c2)
        }
    }()
    time.Sleep(time.Second * 20)
}

运行结果

fatal error: concurrent map read and map write

同时Read(正常)

package main

import (
    "time"
    "fmt"
    "encoding/json"
)

func main() {
    c := make(map[string]int)
    for j := 0; j < 1000000; j++ {
        c[fmt.Sprintf("%d", j)] = j
    }
    go func() { //开一个goroutine读map
        for j := 0; j < 1000000; j++ {
            fmt.Println(c[fmt.Sprintf("%d", j)])
        }
    }()
    go func() { //开一个goroutine读map
        for j := 0; j < 1000000; j++ {
            fmt.Println(c[fmt.Sprintf("%d", j)])
        }
    }()
    time.Sleep(time.Second * 20)
}

运行结果正常

同时Write(异常)

import (
    "time"
    "fmt"
    "encoding/json"
)

func main() {
    c := make(map[string]int)
    go func() { //开一个goroutine写map
        for j := 0; j < 1000000; j++ {
            c[fmt.Sprintf("%d", j)] = j
        }
    }()
    go func() { //开一个goroutine写map
        for j := 0; j < 1000000; j++ {
            c[fmt.Sprintf("%d", j)] = j
        }
    }()
    time.Sleep(time.Second * 20)
}

运行结果

fatal error: concurrent map writes

结论:

1.无论什么情况下len操作总是正常的
2.同时read不会引发异常,同时read和write会异常,同时write会异常。
3.read或write的同时,json.Marshall或json.Unmarshall此类解析方法也应避免使用,否则也会引发异常。

解决方案很多,控制同步使用,或者使用锁,这里就不多说了

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