package main
 
import (
	"fmt"
	"sync"
	"time"
)
 
var l sync.RWMutex
var a string = "1"
 
func f() {
	a = "hello,world"
	l.Unlock()
	//l.RUnlock()
}
 
func main() {
	l.Lock()
	//l.RLock()
	go f()
	l.Lock()Lock()
	//l.URLock()
	fmt.Println(a)
}