Reproduce Golang "fatal error: concurrent map writes" & Solution. To reproduce comment Mutex related all operation like line no. 12, 30, 32, 44, 46. Mutex is use to prevent race condition which generates this error.

fatal_map_writes.go

package main

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

var activeInstances = make(map[int]string)
var wg sync.WaitGroup
var mutex = &sync.Mutex{}

func main(){

	wg.Add(2)
	go setValue()
	go deleteValue()
	wg.Wait()
}

func setValue(){

	i := 0;

	for {
//		time.Sleep(1 * time.Second)
		fmt.Println("In setValue(). Iteration = " + strconv.Itoa(i) + "\n")

		mutex.Lock()
		activeInstances[i] = "In setValue string"
		mutex.Unlock()
		i++
	}
}

func deleteValue(){
	i := 0;

	for {
//		time.Sleep(1 * time.Second)
		fmt.Println("In deleteValue(). Iteration = " + strconv.Itoa(i) + "\n")

		mutex.Lock()
		delete(activeInstances, i)
		mutex.Unlock()
		i++
	}
}