modern-cpp-tutorial/code/7/7.6.atomic.cpp

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

std::atomic<int> count = {0};

int main() {
    std::thread t1([](){
        count.fetch_add(1);
    });
    std::thread t2([](){
        count++;        // identical to fetch_add
        count += 1;     // identical to fetch_add
    });
    t1.join();
    t2.join();
    std::cout << count << std::endl;
    return 0;
}