Cross-thread visibility with a relaxed flag

#include <atomic>
#include <thread>

std::atomic<bool> ready{false};
int data = 0;

void producer() {
    data = 42;
    ready.store(true, std::memory_order_relaxed);
}
void consumer() {
    while (!ready.load(std::memory_order_relaxed)) {}
    std::cout << data;  // may print 0
}