Here is a bad example of creating unique counter id with atomics for blog post

unique_id_with_atomic.cpp

#include <atomic>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <thread>
#include <vector>

int main()
{
    std::atomic_int32_t counter{0};
    //    std::atomic_int64_t all_counted_numbers_count{0};
    std::vector<std::thread> thread_list;

    auto thread_count = std::thread::hardware_concurrency();

    // NOTE In the worst case,this way will lose thread_count-1 number, but doesn't matter
    auto count_per_thread = std::numeric_limits<uint32_t>::max() / thread_count - 1;

    // record start time
    auto start = std::chrono::high_resolution_clock::now();

    for (uint8_t i = 0; i < thread_count; ++i)

    {
        thread_list.push_back(std::thread([&counter, count_per_thread]() {
            for (uint32_t i = 0; i < count_per_thread; ++i)
            {
                auto unique_number = counter++;
            }
            std::clog << count_per_thread << " done" << std::endl;
        }));
    }
    for (auto &thread : thread_list)
    {
        if (thread.joinable())
        {
            thread.join();
        }
    }

    std::cout << "time of all threads " << std::setw(9)
              << std::chrono::duration<double>(std::chrono::high_resolution_clock::now() - start)
                     .count()
              << " s\n";
    std::cout << "Hello World!" << std::endl;
    return 0;
}