Method enqueue

examples/server/httplib.h:603–610

  ~ThreadPool() override = default;

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

    cond_.notify_one();
  }

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