Go slice race condition example

race.go

package main

import (
	"fmt"
	"time"
)

type List struct {
	Items []int
}

func (l *List) Add(i int) {
	l.Items = append(l.Items, i)
}

var GlobalList List

func init() {
	GlobalList = List{}
	for {
		// get case when len != cap
		GlobalList.Add(0)
		if len(GlobalList.Items) < cap(GlobalList.Items) {
			fmt.Println("Initialized that case:", len(GlobalList.Items), cap(GlobalList.Items))
			break
		}
	}
}

func main() {
	// create concurrent writers for "clones" of GlobalList
	for i := 0; i < 2; i++ {
		go func(i int) {
			ticker := time.NewTicker(time.Nanosecond)
			for _ = range ticker.C {
				clone := GlobalList
				clone.Add(i)
				index := len(clone.Items) - 1

				// if thing that we wrote did not match actual value @_@
				if clone.Items[index] != i {
					fmt.Println("add failed by race")
				}
			}
		}(i)
	}

	ticker := time.NewTicker(time.Millisecond * 500)
	for _ = range ticker.C {
		fmt.Println(GlobalList.Items[:cap(GlobalList.Items)])
	}
}