You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: 53_互斥锁.go
    path of file: ./repos/learning/golang/source_code/Go语言基础与提升课程资料/源码
    
    the code of the file until where you have to start completion: package main

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

var f1 = false
var f2 = false
var mutex sync.Mutex //定义互斥锁

func main() {
	go person01("hello")
	go person02("word!")
    
func printer(str string) {
	mutex.Lock()         //加锁
	defer mutex.Unlock() //解锁操作
	for _, data := range str {
		fmt.Printf("%c", data)
		time.Sleep(time.Second * 1)
	}
	fmt.Println()

}