C++ mutex lock,unlock

#model/util.h
#pragma once
#include <chrono>
#include <ctime>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <mutex>
#include <sstream>
#include <stdio.h>
#include <time.h>
#include <thread>
#include <unistd.h>
#include <uuid/uuid.h>
#include <vector>

class util
{
public:

 char *uuid_value;
    char *get_uuid();
    std::string get_str_uuid();
    std::string get_time_now();   
    util();
    ~util();
    util(util &ul) = delete;
    util operator=(util &ul) = delete;
};


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

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

util::util()
{
    uuid_value = (char *)malloc(40);
    std::cout << "In constructor and now is " << get_time_now() << std::endl;
}

util::~util()
{
    std::cout << "In deconstructor and now is " << get_time_now() << 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);
    struct tm tm_info = *localtime(&raw_time);
    std::chrono::milliseconds mills = std::chrono::duration_cast<std::chrono::milliseconds>(now.time_since_epoch());
    std::chrono::seconds seconds = std::chrono::duration_cast<std::chrono::seconds>(now.time_since_epoch());
    std::uint64_t mills_count = mills.count() - seconds.count() * 1000;
    std::stringstream ss;
    ss << std::put_time(&tm_info, "%Y%m%d%H%M%S") << std::setfill('0') << std::setw(3) << std::to_string(mills_count);
    return ss.str();
}

std::string util::get_str_uuid()
{
    uuid_t new_uuid;
    uuid_generate(new_uuid);
    uuid_unparse(new_uuid, uuid_value);
    return std::string(uuid_value);
}


//main.cpp
#include "model/util.h"
std::map<int, std::string> _mutex_map;
std::mutex _lock_unlock_mtx;
void fill_mutext_map(util &ul, const int &len)
{
    _lock_unlock_mtx.lock();
    std::cout << "std::this_thread::get_id()=" << std::this_thread::get_id() << "," << ul.get_time_now() << " started in file:" << std::string(__FILE__) << ",function:" << std::string(__FUNCTION__) + ",line:" << std::to_string(__LINE__) << std::endl;
    static int num = 0;
    for (int i = 0; i < len; i++)
    {
        _mutex_map.insert(std::pair<int, std::string>(++num, ul.get_str_uuid()));
    }
    std::cout << num << ",std::this_thread::get_id()=" << std::this_thread::get_id() << "," << ul.get_time_now() << " finished in file:" << std::string(__FILE__) << ",function:" << std::string(__FUNCTION__) + ",line:" << std::to_string(__LINE__) << std::endl;
    _lock_unlock_mtx.unlock();
}

void mutex_multi_threads(const int &x, const int &y)
{
    util ul;
    std::thread t1(fill_mutext_map, std::ref(ul), std::cref(x));    
    std::thread t2(fill_mutext_map, std::ref(ul), std::cref(y));
    t1.join();
    t2.join();
    std::cout << "_mutex_map.size()=" << _mutex_map.size() << std::endl;
    auto itr = _mutex_map.begin();
    while (itr != _mutex_map.end())
    {
        std::cout << itr->first << "," << itr->second << std::endl;
        itr = std::next(itr, 1000000);
    }
    std::cout << ul.get_time_now() << " finished in file:" << std::string(__FILE__) << ",function:" << std::string(__FUNCTION__) + ",line:" << std::to_string(__LINE__) << std::endl;
}

int main(int argc, char **argv)
{
    mutex_multi_threads(atoi(argv[1]), atoi(argv[2]));
}

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