void
test_concurrent_push_and_pop_on_empty_queue()
{
  threadsafe_queue<int> q;

  std::promise<void> go, push_ready, pop_ready;
  std::shared_future<void> ready(go.get_future());

  std::future<void> push_done;
  std::future<int> pop_done;

  try {
    push_done = std::async(std::launch::async, [&q, ready, &push_ready]() {
      push_ready.set_value();
      ready.wait();
      q.push(42);
    });
    pop_done  = std::async(std::launch::async, [&q, ready, &pop_ready]() {
      pop_ready.set_value();
      ready.wait();
      return q.pop();
    });
    push_ready.get_future().wait();
    pop_ready.get_future().wait();
    go.set_value();

    push_done.get();
    assert(pop_done.get() == 42);
    assert(q.empty());
  }
  catch (...) {
    go.set_value();
    throw;
  }
}