std::promise的使用

std::promise用於多線程間交換數據：

void test1(std::promise<int> &p)
{
    //while (1)
    {
        std::cout<< "test1";
        std::chrono::system_clock t;
        std::cout << std::this_thread::get_id() << endl;
        std::cout<< "test1 quit" <<endl;

        int val = 123;
        cout << "in data" << endl;
        p.set_value(val);
        p.set_value(val);
    }

}

void test2(std::future<int>& f)
{
    //while (1)
    {
        auto val = f.get();
        cout << "val value:" << val;
        std::cout<< "test2";
        std::this_thread::sleep_for(seconds(3));
        std::cout<< "test2 quit"<<endl;
    }

}



int main()
{

    std::promise<int> m;
    std::future<int> n;
    n = m.get_future();

    thread testA(test1, std::ref(m));
    thread testB(test2, std::ref(n));


    testA.join();
    testB.join();

    cout << "Hello World end!" << endl;
    return 0;
}