使用条件变量的线程安全队列

template<typename T>
class threadsafe_queue
{
private:
 mutable std::mutex mut;
 std::queue<T> data_queue;
 std::condition_variable data_cond;
public:
 threadsafe_queue()
 {}
 
 void push(T new_value)
 {
  std::lock_guard<std::mutex> lk(mut);
  data_queue.push(std::move(new_value));
  data_cond.notify_one();
 }
 
 void wait_and_pop(T& value)
 {
  std::unique_lock<std::mutex> lk(mut);
  data_cond.wait(lk, [this]{return !data_queue.empty(); });
  value = std::move(data_queue.front());
  data_queue.pop();
 }
 
 std::shared_ptr<T> wait_and_pop()
 {
  std::unique_lock<std::mutex> lk(mut);
  data_cond.wait(lk, [this]{return !data_queue.empty(); });
  std::shared_ptr<T> res(
   std::make_shared<T>(std::move(data_queue.front())));
  data_queue.pop();
  return res;
 }
 
 bool try_pop(T& value)
 {
  std::lock_guard<std::mutex> lk(mut);
  if (data_queue.empty())
   return false;
  value = std::move(data_queue.front());
  data_queue.pop();
 }
 
 std::shared_ptr<T> try_pop()
 {
  std::lock_guard<std::mutex> lk(mut);
  if (data_queue.empty())
   return std::shared_ptr<T>();
  std::shared_ptr<T> res(
   std::make_shared<T>(std::move(data_queue.front())));
  data_queue.pop();
  return res;
 }
 
 bool empty() const
 {
  std::lock_guard<std::mutex> lk(mut);
  return data_queue.empty();
 }
};
template<typename T>
class threadsafe_queue