template <typename T>
void
threadsafe_queue<T>::push(T new_value)
{
  std::shared_ptr<T> new_data(std::make_shared<T>(std::move(new_value)));
  std::unique_ptr<node> p(new node);
  {
    std::lock_guard<std::mutex> tail_lock(tail_mutex);
    tail->data           = new_data;
    node* const new_tail = p.get();
    tail->next           = std::move(p);
    tail                 = new_tail;
  }
  data_cond.notify_one();
}