localtime-多线程不安全

#include<fstream>
#include<iostream>
#include <map>
#include <unistd.h>
using namespace std;

void*  Fun1(void *arg){
   
    struct tm * tm= (struct tm*)arg;
    tm->tm_mday = tm->tm_mday+1;
    tm->tm_hour = 8;
    tm->tm_min = 0;
    tm->tm_sec = 0;
    usleep(500