std::async to read big text file

main.cpp

#include <string>
#include <set>
#include <future>
#include <iostream>
#include <memory>
#include <fstream>
#include <chrono>

class InputReader {
public:

    std::set<std::string> ReadAll() {
        std::cout << "STARTING" << std::endl; // debug

        std::set<std::string> result;

        std::string word;
        while (ifs >> word)
        {
            result.insert(word);
        }

        return result;
    }

    InputReader(std::istream &ifs) : ifs(ifs) { }

private:

    std::istream &ifs;

};

int main() {
    std::ifstream ifs("test.txt");
    auto reader = std::make_unique<InputReader>(ifs);

    auto f = std::async(std::launch::async, &InputReader::ReadAll, reader.get());

    while (true) {
        int x;
        std::cout << "Something:" << std::endl;
        std::cin >> x;

        if (x == 0) {
            break;
        }

        if (x == 1) {
            std::cout << "Valid? " << std::boolalpha << f.valid() << "\n";
            if (f.valid()) {
                auto s = f.get();
                std::cout << "Size of the set: " << s.size() << "\n";
                std::cout << *s.begin();
            }
        }

    }
}