Method ThreadPool

external/httplib.h:753–759

class ThreadPool final : public TaskQueue {
public:
  explicit ThreadPool(size_t n, size_t mqr = 0)
      : shutdown_(false), max_queued_requests_(mqr) {
    while (n) {
      threads_.emplace_back(worker(*this));
      n--;
    }
  }

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