利用CAS实现自旋锁

class spin_mutex {private:  std::atomic
    
      flag = ATOMIC_VAR_INIT(false);public:  spin_mutex() = default;  spin_mutex(const spin_mutex&) = delete;  spin_mutex& operator= (const spin_mutex&) = delete;  void lock() {    bool expected = false;    while(!flag.compare_exchange_strong(expected, true))      expected = false;  }  void unlock() {    flag.store(false);  }};