pitrou commented on code in PR #48128:
URL: https://github.com/apache/arrow/pull/48128#discussion_r2546450378
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cpp/src/arrow/array/array_nested.cc:
##########
@@ -1076,20 +1076,27 @@ 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_explicit(&boxed_fields_[i],
&expected, result,
Review Comment:
I would feel more confident using simply
`std::atomic_compare_exchange_strong`.
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