package main

import (
	"fmt"
	"sync"
	"time"
)

func increment(l *sync.Mutex, a *int) {
	l.Lock()
	defer l.Unlock()
	*a+=1
}

func main() {
	var l sync.Mutex
	a := 0
	for i := 0; i < 100; i++ {
		go increment(&l, &a)
	}
	fmt.Println("a=", a)
	time.Sleep(time.Second)
}