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I have just started learning parallel programming in c++ and wanted to use HPX for it. I need to complete several tasks in groups of N and I wanted to write code that puts all the threads into a vector and when at least one is done replace it with the next thread.

#include <iostream>
#include <vector>
#include "hpx/hpx_main.hpp"
#include "hpx/future.hpp"

using namespace std;



int dummy(int a){
    return a;
    }
    
int main(){
    vector<hpx::future<int>>futures;
    futures.reserve(3);
    
    for(int step = 0; step < 3; step++){
        futures.push_back(hpx::async(dummy, step));
        }
    
    int index;
    auto f2 = hpx::when_any(futures).then([&](auto f){
        return f;
        });
        
    
    auto res = f2.get();
    vector<hpx::future<int>> fut3 = res.futures;
    for(int i = 0; i < fut3.size(); i++){
        cout << fut3[i].get() << endl;
        }
    }

This code results in a following error:

error: static assertion failed: result type must be constructible from input type

I have tryied to find solutions online, but there is barely any examples of code with hpx.

Василий максимов
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  • It is cogent that you do not use `using namespace std;` when writing HPX code given that a lot of `std::` facilities are reimplemented under `hpx::` and using unqualifed names might confuse the compiler ;) – gonidelis Jan 31 '23 at 00:01
  • Now that I am thinking of, it is not a good thing to use unqualified names in general regardless of HPX. – gonidelis Jan 31 '23 at 00:02

1 Answers1

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Try adding std::move when copying the resulting futures:

std::vector<hpx::future<int>> fut3 = std::move(res.futures);

The problem is that res.futures is invalidaded after the copy.

gonidelis
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