memory_order_relaxed_and_fence.c

// Source: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1525.htm
const int num_mailboxes = 32;
_Atomic volatile int mailbox[num_mailboxes];

void MailboxInspection(int my_id, void (*do_work)(int)) {
    for (int i = 0; i < num_mailboxes; i++) {
        if (atomic_load_explicit(&mailbox[i],  memory_order_relaxed) == my_id) {
            atomic_thread_fence(memory_order_acquire); // prevent speculative reads in do_work [7.17.4.1]
            do_work(i);
        }
    }
}