Major Description
Just before 2.3.0, SPARK-23219 renamed ReadTask to DataReaderFactory. The intent was to make the read and write API match (write side uses DataWriterFactory), but the underlying problem is that the two classes are not equivalent.
ReadTask/DataReader function as Iterable/Iterator. ReadTask is a specific to a read task, in contrast to DataWriterFactory where the same factory instance is used in all write tasks. ReadTask's purpose is to manage the lifecycle of DataReader with an explicit create operation to mirror the close operation. This is no longer clear from the API, where DataReaderFactory appears to be more generic than it is and it isn't clear why a set of them is produced for a read.
We should rename DataReaderFactory back to ReadTask, which correctly conveys the purpose and use of the class.
