[GitHub] [arrow] westonpace commented on a diff in pull request #13205: ARROW-16515: [C++] Adding a Close method to RecordBatchReader

[GitBox <gi...@apache.org>]

westonpace commented on code in PR #13205:
URL: https://github.com/apache/arrow/pull/13205#discussion_r878616768


##########
cpp/src/arrow/record_batch.h:
##########
@@ -243,6 +243,9 @@ class ARROW_EXPORT RecordBatchReader {
     return batch;
   }
 
+  /// \brief finalize reader
+  virtual Status Close() = 0;

Review Comment:
   Instead of making this pure virtual (`= 0`) can you make this virtual and give it an implementation?
   ```suggestion
     virtual Status Close() {
       return Status::OK();
     };
   ```



##########
cpp/src/arrow/dataset/scanner.cc:
##########
@@ -85,6 +85,8 @@ class ScannerRecordBatchReader : public RecordBatchReader {
     return Status::OK();
   }
 
+  Status Close() override { return Status::OK(); }

Review Comment:
   We should execute exec plans until they finish.  So this should look something like...
   ```
   Status Close() override {
     std::shared_ptr<RecordBatch> batch;
     RETURN_NOT_OK(ReadNext(&batch));
     while (batch != nullptr) {
       RETURN_NOT_OK(ReadNext(&batch));
     }
     return Status::OK();
   }
   ```



##########
cpp/src/arrow/compute/exec/exec_plan.cc:
##########
@@ -476,6 +476,8 @@ std::shared_ptr<RecordBatchReader> MakeGeneratorReader(
       return Status::OK();
     }
 
+    Status Close() override { return Status::OK(); }

Review Comment:
   This should read from the generator until the end is reached.



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