Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/7904#discussion_r36579540
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/joins/RowIterator.scala
---
@@ -0,0 +1,63 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.execution.joins
+
+import java.util.NoSuchElementException
+
+import org.apache.spark.sql.catalyst.InternalRow
+
+private[sql] abstract class RowIterator {
+ def advanceNext(): Boolean
+ def getRow: InternalRow
+ def toScala: Iterator[InternalRow] = new RowIteratorToScala(this)
+}
+
+object RowIterator {
+ def fromScala(scalaIter: Iterator[InternalRow]): RowIterator = {
+ scalaIter match {
+ case wrappedRowIter: RowIteratorToScala => wrappedRowIter.rowIter
+ case _ => new RowIteratorFromScala(scalaIter)
+ }
+ }
+}
+
+private final class RowIteratorToScala(val rowIter: RowIterator) extends
Iterator[InternalRow] {
+ private [this] var _hasNext: Boolean = rowIter.advanceNext()
+ override def hasNext: Boolean = _hasNext
+ override def next(): InternalRow = {
+ if (!_hasNext) throw new NoSuchElementException
+ val row: InternalRow = rowIter.getRow.copy()
--- End diff --
Come to think of it, we could quickly figure out whether this copying is
necessary by adding an assertion to detect whether `hasNext()` is ever called
two times in a row. If it's not, then we shouldn't need the copy. We can still
keep the `RowIteratorToScala` class as a wrapper to enforce this guarantee and
can plan to remove it when / if we transition all of our internal iterator
interfaces to use something more like `RowIterator`.
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