单例模式两种实现方法

yunn_2026-05-27 18:10

设计模式

单例模式：

复制代码

#include <iostream>
#include<mutex>

class MyCAS {
private:
  MyCAS() {};
  MyCAS(const MyCAS*) = delete;
  MyCAS& operator=(const MyCAS*) = delete;
private:
  static MyCAS* m_instance;
  static std::mutex m_mutex;

public:

  static MyCAS* GetInstance() {
    if (m_instance == nullptr) {
      std::lock_guard<std::mutex> lock(m_mutex);
      if (m_instance == nullptr) {
        m_instance = new MyCAS();
        static CGarhuishou cl;
      }

    }
    return m_instance;
  };

  class CGarhuishou {
  public:
    ~CGarhuishou() {
      if (MyCAS::m_instance) {
        delete MyCAS::m_instance;
        MyCAS::m_instance = nullptr;
      }
    }
  };
  void func() {
    std::cout << "测试" << std::endl;
  }
};
MyCAS* MyCAS::m_instance = nullptr;
std::mutex MyCAS::m_mutex;

使用std::once_flag ，作为一个标记，std::call_once通过这个标记来决定对应传入的函数是否执行，调用call_once成功后，call_once会反转这个标记，这样再次调用这个call_once后，传入的函数就不会再次被执行了；

复制代码

#include <iostream>
#include<mutex>

class MyCAS {
private:
  MyCAS() {};
  MyCAS(const MyCAS*) = delete;
  MyCAS& operator=(const MyCAS*) = delete;
private:
  static MyCAS* m_instance;

  static std::once_flag m_flag;
public:
  static void CreateInstance() {
    m_instance = new MyCAS();
    static CGarhuishou cl;
  }
  static MyCAS* GetInstance() {

    std::call_once(m_flag, CreateInstance);

    return m_instance;
  };

  class CGarhuishou {
  public:
    ~CGarhuishou() {
      if (MyCAS::m_instance) {
        delete MyCAS::m_instance;
        MyCAS::m_instance = nullptr;
      }
    }
  };
  void func() {
    std::cout << "测试" << std::endl;
  }
};
MyCAS* MyCAS::m_instance = nullptr;

std::once_flag MyCAS::m_flag;