  void remove_handler(Http2Handler *handler) {
    handlers_.erase(handler);
    if (handlers_.empty() && !fd_cache_.empty()) {
      ev_timer_again(loop_, &release_fd_timer_);
    }
  }
  void remove_handler(Http2Handler *handler) {
    handlers_.erase(handler);
    if (handlers_.empty() && !fd_cache_.empty()) {
      ev_timer_again(loop_, &release_fd_timer_);
    }
  }