// http://preshing.com/20120515/memory-reordering-caught-in-the-act

#include "xorshift32.h"
#include <atomic>
#include <functional>
#include <iostream>
#include <random>
#include <semaphore>
#include <thread>

using namespace std::literals;

int x, y, r1, r2;
unsigned reorders = 0, iterations = 0;
std::atomic<bool> run(true);
std::binary_semaphore s1(1), s2(1), s3(1), s4(1);
thread_local xorshift32 rng;

void t1()
{
    while (run)
    {
        s1.acquire();
        while (rng() & 7)
            ;
        x = 1;
        std::atomic_thread_fence(std::memory_order_seq_cst);
        r1 = y;
        s3.release();
    }
}

void t2()
{
    while (run)
    {
        s2.acquire();
        while (rng() & 7)
            ;
        y = 1;
        std::atomic_thread_fence(std::memory_order_seq_cst);
        r2 = x;
        s4.release();
    }
}

void t3()
{
    while (run)
    {
        x = 0;
        y = 0;
        s1.release();
        s2.release();
        s3.acquire();
        s4.acquire();
        if (r1 == 0 && r2 == 0)
            ++reorders;
        ++iterations;
    }
}

int main()
{
    s1.acquire();
    s2.acquire();
    s3.acquire();
    s4.acquire();

    std::jthread t[] = {std::jthread(t1), std::jthread(t2),
                        std::jthread(t3)};

    std::this_thread::sleep_for(500ms);
    run = false;

    s1.release();
    s2.release();
    s3.release();
    s4.release();

    std::cout << reorders << " reorders detected after " << iterations
              << " iterations" << std::endl;
}