Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/15089#discussion_r80130429
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/python/RowQueue.scala ---
@@ -0,0 +1,278 @@
+/*
+* 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.python
+
+import java.io._
+
+import com.google.common.io.Closeables
+
+import org.apache.spark.SparkException
+import org.apache.spark.memory.{MemoryConsumer, TaskMemoryManager}
+import org.apache.spark.sql.catalyst.expressions.UnsafeRow
+import org.apache.spark.unsafe.Platform
+import org.apache.spark.unsafe.memory.MemoryBlock
+
+/**
+ * A RowQueue is an FIFO queue for UnsafeRow.
+ */
+private[python] trait RowQueue {
+ /**
+ * Add a row to the end of it, returns true iff the row has added into
it.
+ */
+ def add(row: UnsafeRow): Boolean
+
+ /**
+ * Retrieve and remove the first row, returns null if it's empty.
+ *
+ * It can only be called after add is called.
+ */
+ def remove(): UnsafeRow
+
+ /**
+ * Cleanup all the resources.
+ */
+ def close(): Unit
+}
+
+/**
+ * A RowQueue that is based on in-memory page. UnsafeRows are appended
into it until it's full.
+ * Another thread could read from it at the same time (behind the writer).
+ *
+ * The format of UnsafeRow in page:
+ * [4 bytes to hold length of record (N)] [N bytes to hold record] [...]
+ */
+private[python] abstract class InMemoryRowQueue(val page: MemoryBlock,
numFields: Int)
+ extends RowQueue {
+ private val base: AnyRef = page.getBaseObject
+ private val endOfPage: Long = page.getBaseOffset + page.size
+ // the first location where a new row would be written
+ private var writeOffset = page.getBaseOffset
+ // points to the start of the next row to read
+ private var readOffset = page.getBaseOffset
+ private val resultRow = new UnsafeRow(numFields)
+
+ def add(row: UnsafeRow): Boolean = {
+ val size = row.getSizeInBytes
+ if (writeOffset + 4 + size > endOfPage) {
+ // if there is not enough space in this page to hold the new record
+ if (writeOffset + 4 <= endOfPage) {
+ // if there's extra space at the end of the page, store a special
"end-of-page" length (-1)
+ Platform.putInt(base, writeOffset, -1)
+ }
+ false
+ } else {
+ Platform.putInt(base, writeOffset, size)
+ Platform.copyMemory(row.getBaseObject, row.getBaseOffset, base,
writeOffset + 4, size)
+ writeOffset += 4 + size
+ true
+ }
+ }
+
+ def remove(): UnsafeRow = {
+ if (readOffset + 4 > endOfPage || Platform.getInt(base, readOffset) <
0) {
+ null
+ } else {
+ val size = Platform.getInt(base, readOffset)
+ resultRow.pointTo(base, readOffset + 4, size)
+ readOffset += 4 + size
+ resultRow
+ }
+ }
+}
+
+/**
+ * A RowQueue that is backed by a file on disk. This queue will stop
accepting new rows once any
+ * reader has begun reading from the queue.
+ */
+private[python] case class DiskRowQueue(file: File, fields: Int) extends
RowQueue {
+ private var fout = new FileOutputStream(file.toString)
+ private var out = new DataOutputStream(new BufferedOutputStream(fout))
+ private var unreadBytes = 0L
+
+ private var fin: FileInputStream = _
+ private var in: DataInputStream = _
+ private val resultRow = new UnsafeRow(fields)
+
+ def add(row: UnsafeRow): Boolean = synchronized {
+ if (out == null) {
+ // Another thread is reading, stop writing this one
+ return false
+ }
+ out.writeInt(row.getSizeInBytes)
+ out.write(row.getBytes)
+ unreadBytes += 4 + row.getSizeInBytes
+ true
+ }
+
+ def remove(): UnsafeRow = synchronized {
+ if (out != null) {
+ out.close()
+ out = null
+ fout.close()
+ fout = null
+
+ fin = new FileInputStream(file.toString)
+ in = new DataInputStream(new BufferedInputStream(fin))
+ }
+
+ if (unreadBytes > 0) {
+ val size = in.readInt()
+ val bytes = new Array[Byte](size)
+ in.readFully(bytes)
+ unreadBytes -= 4 + size
+ resultRow.pointTo(bytes, size)
+ resultRow
+ } else {
+ null
+ }
+ }
+
+ def close(): Unit = synchronized {
+ Closeables.close(fout, true)
+ fout = null
+ Closeables.close(fin, true)
+ fin = null
+ if (file.exists()) {
+ file.delete()
+ }
+ }
+}
+
+/**
+ * A RowQueue that has a list of RowQueues, which could be in memory or
disk.
+ *
+ * HybridRowQueue could be safely appended in one thread, and pulled in
another thread in the same
+ * time.
+ */
+private[python] case class HybridRowQueue(
+ memManager: TaskMemoryManager,
+ tempDir: File,
+ numFields: Int)
+ extends MemoryConsumer(memManager) with RowQueue {
+
+ // Each buffer should have at least one row
+ private var queues = new java.util.LinkedList[RowQueue]()
+
+ private var writing: RowQueue = _
+ private var reading: RowQueue = _
+
+ // exposed for testing
+ private[python] def numQueues(): Int = queues.size()
+
+ def spill(size: Long, trigger: MemoryConsumer): Long = {
+ if (trigger == this) {
+ // When it's triggered by itself, it should write upcoming rows into
disk instead of copying
+ // the rows already in the queue.
+ return 0L
+ }
+ var released = 0L
+ synchronized {
+ // poll out all the buffers and add them back in the same order to
make sure that the rows
+ // are in correct order.
+ val iter = queues.iterator()
+ val newQueues = new java.util.LinkedList[RowQueue]()
+ while (iter.hasNext) {
+ val queue = queues.remove()
--- End diff --
I think this block is still slightly confusing because it's calling
`iter.hasNext()` but never calls `iter.nex()`.
If `LinkedList`'s iterator implements `Iterator.remove()` then I think it
would be preferable to use that.
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