use threads instead loop

[RodrigoDornelles]

I'm a beginner in C++, the solution I was trying was having race conditions problems.

int
main(int argc, char *argv[]) {
    if (argc < 2) {
        std::cerr << "command list:";
        for (const auto &command : commands_list) {
            std::cerr << " " << command.first;
        }
        std::cerr << std::endl;
        return 1;
    }

    std::vector<decltype(commands_list.begin())> commands;
    std::vector<std::stringstream> pipes(argc - 2);
    std::vector<std::thread> threads;

    for (int i = 1; i < argc; ++i) {
        auto command = commands_list.find(argv[i]);
        if (command == commands_list.end()) {
            std::cerr << "Command not found: " << argv[i] << std::endl;
            return 1;
        }
        commands.push_back(command);
    }

    for (size_t i = 0; i < commands.size(); ++i) {
        auto command = commands[i];
        std::istream &pipe_in = (i == 0) ? std::cin : pipes[i - 1];
        std::ostream &pipe_out = (i + 1 == commands.size()) ? std::cout : pipes[i];
        threads.emplace_back(command->second, std::ref(pipe_in), std::ref(pipe_out));
    }
    for (auto &thread : threads) {
        thread.join();
    }
    return 0;
}