Not Atomic operation on Map

map.go

package main

import (
	"log"
	"runtime"
	"sync"
)

var debug func(a ...interface{})

func init() {
	log.SetFlags(log.Lshortfile)
	debug = func(a ...interface{}) {
		log.Printf("%+v", a)
	}
	debug(runtime.NumCPU())
	runtime.GOMAXPROCS(runtime.NumCPU())
}

func main() {
	var wg sync.WaitGroup
	Map := make(map[int]int)
	for i := 0; i < 100000; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			j := Map[0]
			j = j + 1
			Map[0] = j

			actual := Map[0]
			expected := j
			if actual != expected {
				debug(actual, expected)
			}
		}()
	}
	wg.Wait()
}