Method enqueue_impl

3rd/MPMCQueue/include/MPMCQueue.hpp:156–181

  template <typename U>
  [[nodiscard]] auto enqueue_impl(U&& item) noexcept -> bool {
    size_t pos;
    Cell* cell;
    size_t seq;

    pos = head_.load(std::memory_order_relaxed);

    for (;;) {
      cell = &buffer_[pos & (Capacity - 1)];
      seq = cell->sequence.load(std::memory_order_acquire);
      intptr_t diff = static_cast<intptr_t>(seq) - static_cast<intptr_t>(pos);

      if (diff == 0) {
        if (head_.compare_exchange_weak(pos, pos + 1,
                                        std::memory_order_relaxed)) {
          cell->data = std::forward<U>(item);
          cell->sequence.store(pos + 1, std::memory_order_release);
          return true;
        }
      } else if (diff < 0) {
        return false;
      } else {
        pos = head_.load(std::memory_order_relaxed);
      }
    }
  }

  // Cache line padding to avoid false sharing
  static constexpr size_t kCacheLineSize = 64;