memory order SeqCst demo

seq_cst.cpp

#include <thread>
#include <atomic>
#include <assert.h>

using namespace std;

static atomic<int> a = 0;
static atomic<int> b = 0;
static atomic<int> A = 0;
static atomic<int> B = 0;

constexpr auto w_order = memory_order_seq_cst;
constexpr auto r_order = memory_order_seq_cst;

static void threadX()
{
  a.store(1, w_order);
  A = b.load(r_order);
}

static void threadY()
{
  b.store(1, w_order);
  B = a.load(r_order);
}

int main() 
{
  for (int i = 0; i < 10'000; ++i) {
    a = b = A = B = 0;
    auto x = thread(threadX);
    auto y = thread(threadY);
    x.join();
    y.join();
    // fprintf(stderr, "A:%d B:%d\n", A.load(), B.load());
    assert(!(A == 0 && B == 0)); // fails if any of w/r orders are other than SeqCst.
  }
  return 0;
}