package main

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

var wg sync.WaitGroup

//var notify bool

//var exitChan chan bool = make(chan bool, 1)

// why context

func f() {
	defer wg.Done()
	//loop:
	for {
		fmt.Println("hello world")
		time.Sleep(time.Millisecond * 500)
		//if notify {
		//	break
		//} //变量
		//select {
		//case <-exitChan:
		//	break loop
		//default:
		//} //channel 版本
	}

}

func main() {
	wg.Add(1)
	go f()
	time.Sleep(time.Second * 3)
	//如何通知goroutine退出？
	//exitChan <- true
	wg.Wait()

}