Short Example of Race Condition

main.go

package main

import (
	"fmt"
	"time"
)

func main() {
	var v1, v2, v3 int
	var sharedInt int
	stopSignal := false
	doneCh := make(chan bool)

	go func() {
		time.Sleep(1 * time.Second)
		stopSignal = true
	}()

	go func() {
		for stopSignal == false {
			v1++
			sharedInt++
		}
		doneCh <- true
	}()

	go func() {
		for stopSignal == false {
			v2++
			sharedInt++
		}
		doneCh <- true
	}()

	go func() {
		for stopSignal == false {
			v3++
			sharedInt++
		}
		doneCh <- true
	}()

	for i := 0; i < 3; i++ {
		<-doneCh
	}
	fmt.Println("all goroutines have stopped")

	// Because of the race condition the sharedInt
	// will be smaller than the sum of v1, v2 and v3:
	fmt.Println("sharedInt: ", sharedInt)
	fmt.Println("v1+v2+v3:         ", v1+v2+v3)

	// The reason for that is that when multiple goroutines
	// are reading, incrementing and writing to the same variable
	// they eventually will ignore or undo the work of the other
	// goroutines, for example adding 30+1 in all 3 goroutines
	// and then saving 31 3 times in sharedInt.
}