Github user pwendell commented on a diff in the pull request:
https://github.com/apache/spark/pull/3389#discussion_r20682042
--- Diff:
streaming/src/main/scala/org/apache/spark/streaming/dstream/FileInputDStream.scala
---
@@ -17,18 +17,50 @@
package org.apache.spark.streaming.dstream
-import java.io.{ObjectInputStream, IOException}
-import scala.collection.mutable.{HashSet, HashMap}
+import java.io.{IOException, ObjectInputStream}
+
+import scala.Some
+import scala.collection.mutable
+import scala.collection.mutable.HashMap
import scala.reflect.ClassTag
+
import org.apache.hadoop.fs.{FileSystem, Path, PathFilter}
-import org.apache.hadoop.conf.Configuration
import org.apache.hadoop.mapreduce.{InputFormat => NewInputFormat}
-import org.apache.spark.rdd.RDD
-import org.apache.spark.rdd.UnionRDD
-import org.apache.spark.streaming.{StreamingContext, Time}
+import org.apache.spark.rdd.{RDD, UnionRDD}
+import org.apache.spark.streaming._
import org.apache.spark.util.{TimeStampedHashMap, Utils}
-
+/**
+ * This class represents an input stream that monitors a Hadoop-compatible
filesystem for new
+ * files and creates a stream out of them. The way it works as follows.
+ *
+ * This class remembers the information about the files selected in past
batches for
--- End diff --
This goes right into discussing how to work around file visibility issues
but it doesn't discuss anything about the basic operation of the class first.
It might be good to have something first that says:
```
At each batch interval, new files are detected and included in that batch.
In this case "new" means files that became visible to readers during that time
period. Some extra care is needed to deal with the fact that files may become
visible after they are created.
```
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