C++用条件变量实现线程安全的queue容器

#include <queue>
#include <memory>
#include <mutex>
#include <condition_variable>
template<typename T>
class threadsafe_queue
{
   
   
private:
  mutable std::mutex mut;  // 1 互斥量必须是可变的 
  std::queue<T> data_queue;
  std::condition_variable data_cond;
public:
  threadsafe_queue()
  {
   
   }
  threadsafe_queue(threadsafe_queue const& other)
  {
   
   
    std::lock_guard<std::mutex> lk(other.mut);
    data_queue