Method enqueue

deps/httplib/httplib.h:669–676

  ~ThreadPool() override = default;

  void enqueue(std::function<void()> fn) override {
    {
      L_unique_lock<L_mutex> lock(mutex_);
      jobs_.push_back(std::move(fn));
    }

    cond_.notify_one();
  }

  void shutdown() override {
    // Stop all worker threads...