Method ThreadPool

external/cpp-httplib/httplib.h:540–545

    class ThreadPool : public TaskQueue {
    public:
        explicit ThreadPool(size_t n) : shutdown_(false) {
            while (n) {
                threads_.emplace_back(worker(*this));
                n--;
            }
        }

        ThreadPool(const ThreadPool&) = delete;
        ~ThreadPool() override = default;