C++线程安全的模板单例类写法

单例基类定义

#include <memory>
#include <mutex>
#include <iostream>
using namespace std;
template <typename T>
class Singleton {
protected:
    Singleton() = default;
    Singleton(const Singleton<T>&) = delete;
    Singleton& operator=(const Singleton<T>& st) = delete;

    static std::shared_ptr<T> _instance;
public:
    static std::shared_ptr<T> GetInstance() {
        static std::once_flag s_flag;
        std::call_once(s_flag, [&]() {
            _instance = shared_ptr<T>(new T);
            });

        return _instance;
    }
    void PrintAddress() {
        std::cout << _instance.get() << endl;
    }
    ~Singleton() {
        std::cout << "this is singleton destruct" << std::endl;
    }
};

template <typename T>
std::shared_ptr<T> Singleton<T>::_instance = nullptr;

父类继承使用单例类

#include "singleton.h"

class HttpMgr:public Singleton<HttpMgr>,
	public std::enable_shared_from_this<HttpMgr>
{
public:
    ~HttpMgr();
private:
    friend class Singleton<HttpMgr>;
    HttpMgr();
};