一种多线程安全的单例模式

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template <typename T>class StaticSingletonT {public:static T* SafeInstance() {    static T* s_instance_ptr = NULL;    if (!s_instance_ptr) {        if (atomic_compare_exchange(&s_state,             OBJECT_CREATING,             OBJECT_NOT_CREATE) == OBJECT_NOT_CREATE) {                s_instance_ptr = StaticSingletonT<T>::GetInstance();                s_state = OBJECT_CREATED;        } else {            while (s_state != OBJECT_CREATED) usleep(1);            s_instance_ptr = StaticSingletonT<T>::GetInstance();        }    }    return s_instance_ptr;}private:    static T* GetInstance() { static T s_instance; return &s_instance; }private:    enum OBJECT_STATE {        OBJECT_NOT_CREATE = 0,              // Not created        OBJECT_CREATING   = 1,              // Creating        OBJECT_CREATED    = 2               // Has been created    };    static volatile uint32_t s_state;};template<class T> volatile uint32_t StaticSingletonT<T>::s_state = OBJECT_NOT_CREATE;

ps:atomic_compare_exchange换成对应平台支持的API

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