单件模式

单件模式 确保一个类只有一个实例，并提供一个全局访问点。

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


using namespace std;


class Singleton {
public:
    static Singleton *getInstance() {
        if (uniqueInstance == NULL) {
            pthread_mutex_lock (&mutex);
            if (uniqueInstance == NULL) {
                uniqueInstance = new Singleton();
            }
            pthread_mutex_unlock(&mutex);
        }

        return uniqueInstance;
    }

private:
    Singleton() {}
    static Singleton *uniqueInstance;
    static pthread_mutex_t mutex;
};

Singleton *Singleton::uniqueInstance = NULL;
pthread_mutex_t Singleton::mutex = PTHREAD_MUTEX_INITIALIZER;


void *test_singleton(void *arg) {
    Singleton *s = Singleton::getInstance();
    cout << s << endl;
    return NULL;
}

int main(int argc, char **argv)
{
    pthread_t writer_id[10];

    for (int i = 0; i < 10; ++i)
    {
        pthread_create (&writer_id[i], NULL, test_singleton, NULL);
    }

    return 0;
}