Method AddClient

cpp/src/arrow/filesystem/s3fs.cc:847–862

 public:
  Result<std::shared_ptr<S3ClientHolder>> AddClient(std::shared_ptr<S3Client> client) {
    std::unique_lock lock(mutex_);
    if (finalized_) {
      return ErrorS3Finalized();
    }

    auto holder = std::make_shared<S3ClientHolder>(shared_from_this(), std::move(client));

    // Remove expired entries before adding new one
    auto end = std::remove_if(
        holders_.begin(), holders_.end(),
        [](std::weak_ptr<S3ClientHolder> holder) { return holder.expired(); });
    holders_.erase(end, holders_.end());
    holders_.emplace_back(holder);
    return holder;
  }

  void Finalize() {
    std::unique_lock lock(mutex_);