kou commented on code in PR #41824:
URL: https://github.com/apache/arrow/pull/41824#discussion_r1625539769
##########
cpp/src/arrow/util/iterator.h:
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@@ -105,9 +105,18 @@ class Iterator : public
util::EqualityComparable<Iterator<T>> {
Iterator() : ptr_(NULLPTR, [](void*) {}) {}
/// \brief Return the next element of the sequence,
IterationTraits<T>::End() when the
- /// iteration is completed. Calling this on a default constructed Iterator
- /// will result in undefined behavior.
- Result<T> Next() { return next_(ptr_.get()); }
+ /// iteration is completed.
+ Result<T> Next() {
+ if (ptr_) {
+ auto next_result = next_(ptr_.get());
+ if (next_result.ok() && IsIterationEnd(next_result.ValueUnsafe())) {
Review Comment:
Could you explain the reason? Performance?
For the #41771 case:
This is the underlying iterator:
https://github.com/apache/arrow/blob/7f0c4070dd723b2f7e1967d7f7f2cccf6fb256b7/cpp/src/arrow/dataset/scanner.cc#L380-L386
We want to release the IPC reader created at:
https://github.com/apache/arrow/blob/7bc2452b350867b3ddc9de9ceceeef0e4d722941/cpp/src/arrow/dataset/file_ipc.cc#L144
It's referred by the underlying iterator indirectly via
`Future`/`std::function`.
It seems that we can't remove a reference from `Future`/`std::function`
without deleting `Future`/`std::function` and we can't delete
`Future`/`std::function` without deleting the underlying iterator.
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