std::shared_future, std::async, std::launch

#include <thread>
#include <future>
#include <iostream>
                                                                                                                
using std::thread,
    std::promise,
    std::future,
    std::shared_future,
    std::cerr;

int main(){
    int test = 0;
    promise<int> p, p1, p2;
    shared_future<int> sfuture(p.get_future());

    auto task_lambda1 = [sfuture](promise<int>* pr, int l, int* t)->int{
        int n = l * 3 + *t;
        pr->set_value(n);
        sfuture.wait();
        return *t;
    };

    auto task_lambda2 = [sfuture](promise<int>* pr, int l, int* t)->int{
        int n = l *5 + *t;
        pr->set_value(n);
        sfuture.wait();
        return n;
    };

    future<int> a = p1.get_future();
    future<int> b = p2.get_future();

    future<int> result1 = std::async(std::launch::async, task_lambda1, &p1, 10, &test);
    future<int> result2 = std::async(std::launch::async, task_lambda2, &p2, 10, &test);

//  these work if uncommented but don't forget to uncomment
//  the join() calls below.
//  thread s(task_lambda1, &p1, 10, &test);
//  thread t(task_lambda2, &p2, 10, &test);

//  these do not work. pretty sure they're not supposed to
//  in this situation
//  task_lambda1(&p1, 10);
//  task_lambda2(&p2, 10);

    a.wait();
    b.wait();

    test = 17;

//  this is necessary to get everything going
    p.set_value(0);

//  these work if uncommented
//  cerr << "a: " << a.get() << "\n";
//  cerr << "b: " << b.get() << "\n";

    cerr << "result1: " << result1.get() << "\n";
    cerr << "result2: " << result2.get() << "\n";

//  s.join();
//  t.join();

    return 0;
}