singleton.h

template <typename T>
class shared_data {
    public:
        ~shared_data() { }
        explicit shared_data(const shared_data &) = delete;
        shared_data &operator=(const shared_data &) = delete;

        // get shared object of this instance
        static shared_data *get();

        // put object / data
        void put_data(T &data);

        // get object / data
        T &get_data();

    private:
        shared_data() { }

        // make sure write and read are serialized
        std::mutex lock;

        // stored data object
        T data;
};