Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/9428#discussion_r44320330
--- Diff:
core/src/main/scala/org/apache/spark/util/CheckpointingIterator.scala ---
@@ -0,0 +1,225 @@
+/*
+ * 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 java.util.concurrent.ConcurrentHashMap
+
+import scala.reflect.ClassTag
+import scala.util.control.NonFatal
+
+import org.apache.hadoop.fs.{FileSystem, Path}
+
+import org.apache.spark._
+import org.apache.spark.broadcast.Broadcast
+import org.apache.spark.rdd.{RDD, ReliableCheckpointRDD}
+import org.apache.spark.storage.RDDBlockId
+
+/**
+ * Wrapper around an iterator which writes checkpoint data to HDFS while
running action on
+ * an RDD.
+ *
+ * @param id the unique id for a partition of an RDD
+ * @param values the data to be checkpointed
+ * @param fs the FileSystem to use
+ * @param tempOutputPath the temp path to write the checkpoint data
+ * @param finalOutputPath the final path to move the temp file to when
finishing checkpointing
+ * @param context the task context
+ * @param blockSize the block size for writing the checkpoint data
+ */
+private[spark] class CheckpointingIterator[T: ClassTag](
+ id: RDDBlockId,
+ values: Iterator[T],
+ fs: FileSystem,
+ tempOutputPath: Path,
+ finalOutputPath: Path,
+ context: TaskContext,
+ blockSize: Int) extends Iterator[T] with Logging {
+
+ private[this] var completed = false
+
+ context.addTaskCompletionListener { ctx =>
+ // We don't know if the task is successful. So it's possible that we
still checkpoint the
+ // remaining values even if the task is failed.
+ // TODO optimize the failure case if we can know the task status
+ complete()
+ }
+
+ private[this] val fileOutputStream = {
+ val bufferSize = SparkEnv.get.conf.getInt("spark.buffer.size", 65536)
+ if (blockSize < 0) {
+ fs.create(tempOutputPath, false, bufferSize)
+ } else {
+ // This is mainly for testing purpose
+ fs.create(tempOutputPath, false, bufferSize,
fs.getDefaultReplication, blockSize)
+ }
+ }
+
+ private[this] val serializeStream =
+ SparkEnv.get.serializer.newInstance().serializeStream(fileOutputStream)
+
+ /**
+ * 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.
+ */
+ private[this] def complete(): Unit = {
+ if (completed) {
+ return
+ }
+
+ if (serializeStream == null) {
+ // There is some exception when creating serializeStream, we only
need to clean up the
+ // resources.
+ cleanup()
+ return
+ }
+
+ while (values.hasNext) {
+ serializeStream.writeObject(values.next)
+ }
+
+ completed = true
+ CheckpointingIterator.releaseLockForPartition(id)
+ 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)
+ }
+ }
+ }
+
+ private[this] def cleanup(): Unit = {
+ completed = true
+ CheckpointingIterator.releaseLockForPartition(id)
+ if (serializeStream != null) {
+ serializeStream.close()
+ }
+ fs.delete(tempOutputPath, false)
+ }
+
+ override def hasNext: Boolean = {
+ try {
+ val r = values.hasNext
+ if (!r) {
+ complete()
+ }
+ r
+ } catch {
+ case e: Throwable =>
+ try {
+ cleanup()
+ } catch {
+ case NonFatal(e1) =>
+ // Log `e1` since we should not override `e`
+ logError(e1.getMessage, e1)
+ }
+ throw e
+ }
+ }
+
+ override def next(): T = {
+ try {
+ val value = values.next()
+ serializeStream.writeObject(value)
+ value
+ } catch {
+ case e: Throwable =>
--- End diff --
maybe we should put this in a private method? Something like `def
cleanupOnFailure(body: => T)`
```
try {
body
} catch {
case NonFatal(e) => ...
}
```
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