c++ – Which of these Boost Asio multithread tcp server examples is more correct?

Have seen two different examples of this and what/which one is correct?

1. std::vector<std::thread> threads;

2. boost::asio::io_context io_context{(int)threads};

std::vector<std::thread> threads;
auto count = std::thread::hardware_concurrency();
for (unsigned int n = 0; n < count; ++n) {
    threads.emplace_back([&] { io_context->run(); });
}

for (auto &thread : threads) {
    if (thread.joinable())
        thread.join();
}

auto threads = std::thread::hardware_concurrency();
boost::asio::io_context io_context{(int)threads};

std::vector<std::thread> v;
v.reserve(threads - 1);
for(auto i = threads - 1; i > 0; --i)
    v.emplace_back(
        [&io_context]
        {
            io_context.run();
        });
io_context.run();