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General Concepts

Challenge: Implement Race Condition on a Map in Go

Problem Statement

  1. Create one function that will read the value of the data and one function that will update the value.
  2. Place them inside goroutines to make both of them run concurrently.
  3. Add a time.Sleep function at the end to ensure that the main goroutine doesn’t exit.
Note: The time.Sleep function is just a workaround. Don’t use it to make your main goroutine complete its functions. Instead, use WaitGroup.


Create a main.go file in your directory. Add the below code.

package main

import (

func read(sharedMap map[int]int) {
	for {
		_ = sharedMap[0]

func write(sharedMap map[int]int) {
	for {
		sharedMap[0] = sharedMap[0] + 1

func main() {
	sharedMap := make(map[int]int)
	sharedMap[0] = 0

	go read(sharedMap)
	go write(sharedMap)
	time.Sleep(2 * time.Second)

To test this code, fire go run . in your terminal to see the output.

fatal error: concurrent map read and map write

You’ll get the error fatal error: concurrent map read and map write if you execute the above code widget because read and write goroutines are accessing the sharedMap variable at the same time.