std::atomic<Singleton*> Singleton::m_instance;
std::mutex Singleton::m_mutex;

Singleton* Singleton::getInstance() {
    Singleton* tmp = m_instance.load();
    if (tmp == nullptr) {
        std::lock_guard<std::mutex> lock(m_mutex);
        tmp = m_instance.load();
        if (tmp == nullptr) {
            tmp = new Singleton;
            m_instance.store(tmp);
        }
    }
    return tmp;
}