demo how std::atomic can fix race conditions

main.cpp

#include <atomic>
#include <thread>
#include <iostream>
#include <string>

static constexpr int ITERATIONS = 1000000;

int main() {
    // std::atomic<long long> num{0};
    long long num{0};
    auto increment_num = [&num]() {
        for (int i = 0; i < ITERATIONS; ++i) {
            ++num;
        }
    };
    auto t1 = std::thread(increment_num);
    auto t2 = std::thread(increment_num);
    t2.join();
    t1.join();
    std::cout << std::to_string(num) << std::endl;
    return 0;
}