Solve the problem of concurrent map writes in go language

Author: Chen Jinjian
personal blog: HTTPS: //jian1098.github.io
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Contact: jian1098 @qq.com

Run the following program will report an errorfatal error: concurrent map writes

package main

import "time"

var m = make(map[int]int)
func main() {
    
    
   for i := 0; i < 10; i++ {
    
    
      go func(n int) {
    
    
         m[n]=n
      }(i)
   }
   time.Sleep(time.Duration(2)*time.Second)
}

The reason is that the map is a reference type. Concurrent writes to the map will cause competition when high concurrency. An error will be reported regardless of whether the same key is the same or not, and concurrent reads to the map will not cause problems.

Solution one

Replace map with sync.Map

package main

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

var m sync.Map
func main() {
    
    
   for i := 0; i < 10; i++ {
    
    
      go func(n int) {
    
    
         m.Store("a",n)    //写入
      }(i)
   }
   time.Sleep(time.Duration(2)*time.Second)
   fmt.Println(m.Load("a"))   //读取
   //遍历
   m.Range(func(k, v interface{
    
    }) bool {
    
    
      fmt.Println( k, v)
      return true
   })
}

Solution two

Lock

package main

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

var m = make(map[int]int)
var lock sync.Mutex

func main() {
    
    
   for i := 0; i < 10; i++ {
    
    
      go func(n int) {
    
    
         lock.Lock()       //加锁,加锁期间其他协程会进入阻塞状态直到解锁
         time.Sleep(time.Duration(2)*time.Second)
         fmt.Println(n,"在执行")
         m[n]=n
         lock.Unlock()  //解锁
      }(i)
   }
   time.Sleep(time.Duration(20)*time.Second)
}