C++标准库类std::shared_future

#include <iostream>
#include <thread>
#include <future>

void promise_string(std::promise<std::string> &pr)
{
    for (int i = 0; i < 100; i++)
    {
        std::this_thread::sleep_for(std::chrono::milliseconds(10));
        std::cout << "sleep" << std::endl;
    }

    std::string str = "the current function name is: ";
    str.append(__FUNCTION__);
    pr.set_value(str);
}

int main()
{
    std::promise<std::string> pr;
    std::future<std::string> fu(pr.get_future());
    std::shared_future<std::string> sfu(fu.share());

    std::thread t1([&sfu]() {
        std::string str = sfu.get();
        std::cout << "thread1 function is: " << str.c_str() << std::endl;
    });

    std::thread t2([&sfu]() {
        std::string str = sfu.get();
        std::cout << "thread2 function is: " << str.c_str() << std::endl;
    });

    std::async(std::launch::async, [&pr]() {
        promise_string(pr);
    });
    //std::async(std::launch::async, promise_string,ref(pr));

    t1.join();
    t2.join();
    system("pause");
}