#include <atomic>
#include <memory>

template <typename T>
class lock_free_stack {
private:
  struct node;
  struct counted_node_ptr {
    int external_count;
    node* ptr;
  };
  struct node {
    std::shared_ptr<T> data;
    std::atomic<int> internal_count;
    counted_node_ptr next;
    node(T const& data_) : data(std::make_shared<T>(data_)), internal_count(0)
    {
    }
  };
  std::atomic<counted_node_ptr> head;

public:
  ~lock_free_stack()
  {
    while (pop())
      ;
  }
  void push(T const& data)
  {
    counted_node_ptr new_node;
    new_node.ptr            = new node(data);
    new_node.external_count = 1;
    new_node.ptr->next      = head.load();
    while (!head.compare_exchange_weak(new_node.ptr->next, new_node))
      ;
  }
};