gistfile1.txt

namespace {
struct Storage {
  std::atomic<std::uint64_t> futex_{0};
  std::atomic<std::uint64_t> next_;
  std::aligned_storage_t<48, 8> storage_;
};

template <typename Waiter>
void transferCurrentException(Waiter* waiter) {
  assert(std::current_exception());
  new (&waiter->storage_) std::exception_ptr{std::current_exception()};
  waiter->futex_.store(1, std::memory_order_release);
}

template <template <typename> class Atom = std::atomic>
void concurrentExceptionPropagationStress(
    int,
    std::chrono::milliseconds) {
  auto exceptions = std::vector<std::unique_ptr<Storage>>{};
  exceptions.resize(1000000);
  for (auto i = std::size_t{0}; i < exceptions.size(); ++i) {
    exceptions[i] = std::make_unique<Storage>();
  }
  auto throwing = std::function<void(std::uint64_t)>{[&](auto counter) {
    if (counter % 2) {
      throw std::runtime_error{folly::to<std::string>(counter)};
    }
  }};

  std::cout << "Started test" << std::endl;
  auto writer = std::thread{[&]() {
    for (auto i = std::size_t{0}; i < exceptions.size(); ++i) {
      try {
        std::this_thread::yield();
        throwing(i);
      } catch (...) {
        transferCurrentException(exceptions.at(i).get());
        continue;
      }

      exceptions.at(i)->futex_.store(2, std::memory_order_release);
    }
  }};

  auto reader = std::thread{[&]() {
    for (auto i = std::size_t{0}; i < exceptions.size(); ++i) {
      auto value = std::uint64_t{};
      while (!(value = exceptions.at(i)->futex_.load(std::memory_order_acquire))) {}

      if (value == 1) {
        try {
          auto buf = reinterpret_cast<std::exception_ptr*>(&exceptions.at(i)->storage_);
          auto ex = folly::launder(buf);
          auto copy = std::move(*ex);
          ex->exception_ptr::~exception_ptr();
          std::rethrow_exception(std::move(copy));
        } catch (std::exception& exc) {
          assert(folly::to<std::uint64_t>(exc.what()) == i);
        }
      }
    }
  }};

  reader.join();
  writer.join();
}
} // namespace