shared_future.cpp

#include <future>
#include <iostream>
#include <thread>
using namespace std;


int factorial(std::shared_future<int> f){
    int N = f.get();
    int res = 1;
    for(int i=2;i<=N;i++){
        res *= i;
    }

    return res;
}

int main(){

    std::promise<int> p;
    std::future<int> f = p.get_future();
    std::shared_future<int> sf = f.share();

    std::future<int> fu = std::async(std::launch::async,factorial, sf);
    std::future<int> fu2 = std::async(std::launch::async,factorial, sf);
    std::future<int> fu3 = std::async(std::launch::async,factorial, sf);

    // do something else
    std::this_thread::sleep_for(chrono::milliseconds(1000));

    p.set_value(6);

    int x = fu.get();
    cout <<"the result x is : " << x << endl;

    // p.set_value(8);
    int x2 = fu2.get();
    cout <<"the result x2 is : " << x << endl;

    int x3 = fu3.get();
    cout << "the result x3 is: " << x3 << endl;

}