#include <exception>
#include <memory>

struct empty_stack : std::exception {
  const char* what() const throw();
};

template <typename T>
class threadsafe_stack {
public:
  threadsafe_stack();
  threadsafe_stack(const threadsafe_stack&);
  threadsafe_stack& operator=(const threadsafe_stack&) = delete;

  void push(T new_value);
  std::shared_ptr<T> pop();
  void pop(T& value);
  bool empty() const;
};

int
main()
{
}