#include <iostream> // std::cout
#include <atomic>   // std::atomic, std::memory_order_relaxed
#include <thread>   // std::thread

std::atomic_int foo(0);

void print_foo()
{
    int x;
    do
    {
        x = foo.load(std::memory_order_relaxed); // get value atomically
    } while (x == 0);
    std::cout << "foo: " << x << '\n';
    // std::this_thread::sleep_for(std::chrono::seconds(10));
}

void set_foo(int x)
{
    foo.store(x, std::memory_order_relaxed); // set value atomically
}

int main()
{
    std::thread first(print_foo);
    std::thread second(set_foo, 10);
    first.join();
    second.join();
    return 0;
}