cpp once_flag,call_once in mutex

//util.h
#pragma once
#include <chrono>
#include <ctime>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <map>
#include <memory>
#include <mutex>
#include <sstream>
#include <string>
#include <thread>
#include <unistd.h>
#include <uuid/uuid.h>
#include <vector>

class util
{
public:
    std::string get_time_now();
    char *get_uuid();
    util();
    ~util();
    util(const util &ul) = delete;
    util &operator=(util &&ul) = delete;
    char *uuid_value = (char *)malloc(40); 
    std::once_flag of;
    std::map<int, std::string> _once_flag_map;
    static void call_once_func(util &ul, const int &len);
    static void fill_once_flag_map(util &ul, const int &len);
    void mt_call_once_func(util &ul, const int &x, const int &y, const int &z);
};


//model/util.cpp
#include "model/util.h"

void util::mt_call_once_func(util &ul, const int &x, const int &y, const int &z)
{
    std::cout << get_time_now() << ",thread id:" << std::this_thread::get_id() << ", start in " << std::string(__FUNCTION__) << std::endl;
    std::thread t1(call_once_func,std::ref(ul),std::cref(x));
    std::thread t2(call_once_func,std::ref(ul),std::cref(y));
    std::thread t3(call_once_func,std::ref(ul),std::cref(z));
    t1.join();
    t2.join();
    t3.join();
    std::cout << "Size=" << _once_flag_map.size() << std::endl;
    auto itr = _once_flag_map.begin();
    while (itr != _once_flag_map.end())
    {
        std::cout << "Key=" << itr->first << ",value=" << itr->second << std::endl;
        itr++;
    }
    std::cout << get_time_now() << ",thread id:" << std::this_thread::get_id() << ", finish in " << std::string(__FUNCTION__) << std::endl;
}

void util::call_once_func(util &ul, const int &len)
{
    std::call_once(ul.of, fill_once_flag_map,std::ref(ul),std::cref(len));
} 

void util::fill_once_flag_map(util &ul, const int &len)
{
    std::cout << ul.get_time_now() << ",thread id:" << std::this_thread::get_id() << ", start in " << std::string(__FUNCTION__) << std::endl;
    static int num = 0;
    for (int i = 0; i < len; i++)
    {
        ul._once_flag_map.insert(std::pair<int, std::string>(++num, ul.get_uuid()));
    }
    std::cout << ul.get_time_now() << ",thread id:" << std::this_thread::get_id() << ", finish in " << std::string(__FUNCTION__) << std::endl;
}

char *util::get_uuid()
{
    uuid_t new_uuid;
    uuid_generate(new_uuid);
    uuid_unparse(new_uuid, uuid_value);
    return uuid_value;
} 

util::util()
{
    std::cout << get_time_now() << " in constructor!" << std::endl;
}

util::~util()
{
    std::cout << get_time_now() << " in decontructor!" << std::endl;
}

std::string util::get_time_now()
{
    std::chrono::time_point<std::chrono::high_resolution_clock> now = std::chrono::high_resolution_clock::now();
    time_t raw_time = std::chrono::high_resolution_clock::to_time_t(now);
    std::chrono::seconds seconds = std::chrono::duration_cast<std::chrono::seconds>(now.time_since_epoch());
    std::chrono::milliseconds mills = std::chrono::duration_cast<std::chrono::milliseconds>(now.time_since_epoch());
    struct tm tm_info = *localtime(&raw_time);
    std::stringstream ss;
    ss << std::put_time(&tm_info, "%Y%m%d%H%M%S") << std::setw(3) << std::setfill('0') << (mills.count() - seconds.count() * 1000);
    return ss.str();
}


//main.cpp
#include "model/util.h"
 
void mt_call_once_func_demo(const int &x, const int &y, const int &z)
{
    util ul;
    ul.mt_call_once_func(std::ref(ul),std::cref(x),std::cref(y),std::cref(z));
}

int main(int args,char **argv)
{
    mt_call_once_func_demo(atoi(argv[1]),atoi(argv[2]),atoi(argv[3]));
}

g++ -g -std=c++2a -I. *.cpp ./model/*.cpp -o h1 -luuid -lpthread

./h1 10 10 10