Singleton Pattern combined with Template

Singleton Pattern 是软件设计中比较常用到的一个模式，有些时候需要将多个class都设计为Singleton，那除了copy and paste之外，还有啥更好的方法呢？C++ Template机制就提供了一个很好的手段。如下代码就是这样的一种实现，compiled and tested with Linux 2.6.18 and gcc 4.1.1

 

//TemplateSingleton.cpp

//please compile with g++ TemplateSingleton -lpthread

 

#include <iostream>
#include <pthread.h>

using namespace std;

template <class T>
class Singleton
{
protected:
    Singleton();
   
public:
    static T* t_;                 
    static pthread_mutex_t m_;                //Each template class or function generated from a template has its own copies of any static variables or members.
   
    static T* getInstance();
};

class C1
{
    friend class Singleton<C1>;
protected:
    C1() {cout << "C1 constructor" << endl;}
    ~C1() {cout << "C1 destructor" << endl;}
};

class C2
{
    friend class Singleton<C2>;
protected:
    C2() {cout << "C2 constructor" << endl;}
    ~C2() {cout << "C2 destructor" << endl;}
};

template <class T> T* Singleton<T>::t_ = 0;
template <class T> pthread_mutex_t Singleton<T>::m_;

template <class T> T* Singleton<T>::getInstance()
{
    if (t_ == 0)    //try to comment out this line and the line with pthread_mutex_unlock to confirm that m_ is not shared by Singleton<C1> and Singleton<C2>
    {
        pthread_mutex_lock(&m_);
        if (t_ == 0)
            t_ = new T;
        pthread_mutex_unlock(&m_);
    }

    return t_;
}

int main(void)
{
    {
    C1* c1 = Singleton<C1>::getInstance();
    C2* c2 = Singleton<C2>::getInstance();

    cout << "c1 address: 0x" << hex << &c1 << dec << endl;
    cout << "c2 address: 0x" << hex << &c2 << dec << endl;

    cout << "c1 points to: 0x" << hex << c1 << dec << endl;
    cout << "c2 points to: 0x" << hex << c2 << dec << endl;

//    delete c1;                   //C1 is protected for construction and destruction
    }

    {
    C1* c3 = Singleton<C1>::getInstance();
    C2* c4 = Singleton<C2>::getInstance();

    cout << "c3 address: 0x" << hex << &c3 << dec << endl;
    cout << "c4 address: 0x" << hex << &c4 << dec << endl;

    cout << "c3 points to: 0x" << hex << c3 << dec << endl;
    cout << "c4 points to: 0x" << hex << c4 << dec << endl;   
    }
}

 

 

 

 

有了Singleton class 之后，其他真正想实现为Singleton Pattern的class就不用再考虑和该pattern相关的逻辑了，只需要在常规class定义的基础上做出如下改动
1。 申明构造函数为protected
2.  申明友元friend class Singleton<ClassName>;

在需要用到Singleton Instance的地方，只要作如下调用即可
ClassName* c1 = Singleton<ClassName>::getInstance();