Copilot commented on code in PR #50158:
URL: https://github.com/apache/arrow/pull/50158#discussion_r3396204823
##########
cpp/src/parquet/arrow/reader.cc:
##########
@@ -825,10 +824,17 @@ Status StructReader::BuildArray(int64_t
length_upper_bound,
END_PARQUET_CATCH_EXCEPTIONS
// Gather children arrays and def levels
- for (auto& child : children_) {
- std::shared_ptr<ChunkedArray> field;
- RETURN_NOT_OK(child->BuildArray(validity_io.values_read, &field));
- ARROW_ASSIGN_OR_RAISE(std::shared_ptr<ArrayData> array_data,
ChunksToSingle(*field));
+ const int num_children = static_cast<int>(children_.size());
Review Comment:
`children_.size()` is `size_t`, and narrowing it via `static_cast<int>` can
silently truncate for large values. Prefer using a checked/narrowing-safe cast
helper (e.g., Arrow's checked_cast/narrow_cast) or keep the task count in a
wider integer type if supported by `OptionalParallelFor` to avoid potential
overflow/truncation.
##########
cpp/src/parquet/arrow/reader.cc:
##########
@@ -735,10 +735,9 @@ class PARQUET_NO_EXPORT StructReader : public
ColumnReaderImpl {
bool IsOrHasRepeatedChild() const final { return has_repeated_child_; }
Status LoadBatch(int64_t records_to_read) override {
- for (const std::unique_ptr<ColumnReaderImpl>& reader : children_) {
- RETURN_NOT_OK(reader->LoadBatch(records_to_read));
- }
- return Status::OK();
+ return ::arrow::internal::OptionalParallelFor(
+ ctx_->reader_properties->use_threads(),
static_cast<int>(children_.size()),
+ [&](int i) { return children_[i]->LoadBatch(records_to_read); });
Review Comment:
`children_.size()` is `size_t`, and narrowing it via `static_cast<int>` can
silently truncate for large values. Prefer using a checked/narrowing-safe cast
helper (e.g., Arrow's checked_cast/narrow_cast) or keep the task count in a
wider integer type if supported by `OptionalParallelFor` to avoid potential
overflow/truncation.
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