设计模式

单例模式    http://blog.csdn.net/hackbuteer1/article/details/7460019

 

#include<stdio.h>                                                                                                                                     
#include<pthread.h>
#include<memory>
class Lock{
private:
    pthread_mutex_t _mutex;
public:
    Lock(){
        pthread_mutex_init(&_mutex, NULL);
    }   
    ~Lock(){
        pthread_mutex_destroy(&_mutex);
    }   
    void lock(){
        pthread_mutex_lock(&_mutex);
    }   
    void unlock(){
        pthread_mutex_unlock(&_mutex);
    }   
};
 
class Guard{
public:
    explicit Guard(Lock* lock){
        _lock = lock;
        if(_lock){
            _lock->lock();
        }   
    }   
    ~Guard(){
        if(_lock){
            _lock->unlock();
        }   
    }   
private:
    Lock* _lock;
};
                                                                                                                                                      
 
class Singleton{
private:
    Singleton(){}
    virtual ~Singleton(){}
    Singleton(const Singleton &){}
    Singleton& operator=(const Singleton&){}
    static Singleton * _instance;
    static Lock _lock;
public:
    static Singleton* get_instance(){
        if (_instance == NULL){
            Guard guard(&_lock);
            if(_instance == NULL){
                _instance = new(std::nothrow) Singleton();
                if(_instance == NULL){
                    perror("new instance FATAL");
                    return NULL;
                }
            }
        }
        return _instance;
    }
    void do_sth(){
        printf("this is a singleton\n");
    }
};
 
Singleton * Singleton::_instance = NULL;
Lock Singleton::_lock;
 
int main(int argc, char* argv[]){
    Singleton* sing = Singleton::get_instance();
        sing->do_sth();                                                                                                                                   
    return 0;
}