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GH-48134: [C++] Make StructArray::field() thread-safe #48128

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Merged
merged 1 commit into from
Nov 20, 2025
+18 −13
Merged

GH-48134: [C++] Make StructArray::field() thread-safe #48128

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29 changes: 17 additions & 12 deletions cpp/src/arrow/array/array_nested.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -1076,20 +1076,25 @@ const ArrayVector& StructArray::fields() const {
return boxed_fields_;
}

const std::shared_ptr<Array>& StructArray::field(int i) const {
std::shared_ptr<Array> StructArray::field(int i) const {
std::shared_ptr<Array> result = std::atomic_load(&boxed_fields_[i]);
if (!result) {
std::shared_ptr<ArrayData> field_data;
if (data_->offset != 0 || data_->child_data[i]->length != data_->length) {
field_data = data_->child_data[i]->Slice(data_->offset, data_->length);
} else {
field_data = data_->child_data[i];
}
result = MakeArray(field_data);
std::atomic_store(&boxed_fields_[i], std::move(result));
return boxed_fields_[i];
if (result) {
return result;
}
return boxed_fields_[i];
std::shared_ptr<ArrayData> field_data;
if (data_->offset != 0 || data_->child_data[i]->length != data_->length) {
field_data = data_->child_data[i]->Slice(data_->offset, data_->length);
} else {
field_data = data_->child_data[i];
}
result = MakeArray(field_data);
// Check if some other thread inserted the array in the meantime and return
// that in that case.
std::shared_ptr<Array> expected = nullptr;
if (!std::atomic_compare_exchange_strong(&boxed_fields_[i], &expected, result)) {
result = std::move(expected);
}
return result;
}

std::shared_ptr<Array> StructArray::GetFieldByName(const std::string& name) const {
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2 changes: 1 addition & 1 deletion cpp/src/arrow/array/array_nested.h
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Original file line number Diff line number Diff line change
Expand Up @@ -692,7 +692,7 @@ class ARROW_EXPORT StructArray : public Array {
// Return a shared pointer in case the requestor desires to share ownership
// with this array. The returned array has its offset, length and null
// count adjusted.
const std::shared_ptr<Array>& field(int pos) const;
std::shared_ptr<Array> field(int pos) const;

const ArrayVector& fields() const;

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