Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/7021#discussion_r33971920
--- Diff:
core/src/main/scala/org/apache/spark/util/CheckpointingIterator.scala ---
@@ -0,0 +1,151 @@
+/*
+ * 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.util
+
+import java.io.IOException
+
+import scala.reflect.ClassTag
+
+import org.apache.hadoop.fs.FileSystem
+import org.apache.hadoop.fs.Path
+
+import org.apache.spark._
+import org.apache.spark.broadcast.Broadcast
+import org.apache.spark.rdd.CheckpointRDD
+import org.apache.spark.serializer.SerializationStream
+
+/**
+ * Wrapper around an iterator which writes checkpoint data to HDFS while
running action on
+ * a RDD to support checkpointing RDD.
+ */
+private[spark] class CheckpointingIterator[A: ClassTag](
+ values: Iterator[A],
+ path: String,
+ broadcastedConf: Broadcast[SerializableConfiguration],
+ partitionId: Int,
+ context: TaskContext,
+ blockSize: Int = -1) extends Iterator[A] with Logging {
+
+ private val env = SparkEnv.get
+ private var fs: FileSystem = null
+ private val bufferSize = env.conf.getInt("spark.buffer.size", 65536)
+ private var serializeStream: SerializationStream = null
+
+ private var finalOutputPath: Path = null
+ private var tempOutputPath: Path = null
+
+ /**
+ * Initialize this iterator by creating temporary output path and
serializer instance.
+ *
+ */
+ def init(): this.type = {
+ val outputDir = new Path(path)
+ fs = outputDir.getFileSystem(broadcastedConf.value.value)
+
+ val finalOutputName = CheckpointRDD.splitIdToFile(partitionId)
+ finalOutputPath = new Path(outputDir, finalOutputName)
+ tempOutputPath =
+ new Path(outputDir, "." + finalOutputName + "-attempt-" +
context.attemptNumber)
+
+ if (fs.exists(tempOutputPath)) {
+ // There are more than one iterator of the RDD is consumed.
+ // Don't checkpoint data in this iterator.
+ doCheckpoint = false
+ return this
+ }
+
+ val fileOutputStream = if (blockSize < 0) {
+ fs.create(tempOutputPath, false, bufferSize)
+ } else {
+ // This is mainly for testing purpose
+ fs.create(tempOutputPath, false, bufferSize,
fs.getDefaultReplication, blockSize)
+ }
+ val serializer = env.serializer.newInstance()
+ serializeStream = serializer.serializeStream(fileOutputStream)
+ this
+ }
+
+ /**
+ * Called when this iterator is on the latest element by `hasNext`.
+ * This method will rename temporary output path to final output path of
checkpoint data.
+ */
+ def completion(): Unit = {
+ if (!doCheckpoint) {
+ return
+ }
+
+ serializeStream.close()
+
+ if (!fs.rename(tempOutputPath, finalOutputPath)) {
+ if (!fs.exists(finalOutputPath)) {
+ logInfo("Deleting tempOutputPath " + tempOutputPath)
+ fs.delete(tempOutputPath, false)
+ throw new IOException("Checkpoint failed: failed to save output of
task: "
+ + context.attemptNumber + " and final output path does not
exist")
+ } else {
+ // Some other copy of this task must've finished before us and
renamed it
+ logInfo("Final output path " + finalOutputPath + " already exists;
not overwriting it")
+ fs.delete(tempOutputPath, false)
+ }
+ }
+ }
+
+ def checkpointing(item: A): Unit = {
+ serializeStream.writeObject(item)
+ }
+
+ override def next(): A = {
+ val item = values.next()
+ if (doCheckpoint) {
+ checkpointing(item)
+ }
+ // If this the latest item, call hasNext will write to final output
early.
+ hasNext
+ item
+ }
+
+ private[this] var doCheckpoint = true
+ private[this] var completed = false
--- End diff --
please declare all variables at the top
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