Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/19136#discussion_r138546295
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/sources/v2/reader/ReadTask.java ---
@@ -0,0 +1,43 @@
+/*
+ * 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.sources.v2.reader;
+
+import java.io.Serializable;
+
+/**
+ * A read task returned by a data source reader and is responsible to
create the data reader.
+ * The relationship between `ReadTask` and `DataReader` is similar to
`Iterable` and `Iterator`.
+ *
+ * Note that, the read task will be serialized and sent to executors, then
the data reader will be
+ * created on executors and do the actual reading.
+ */
+public interface ReadTask<T> extends Serializable {
+ /**
+ * The preferred locations for this read task to run faster, but Spark
can't guarantee that this
+ * task will always run on these locations. Implementations should make
sure that it can
+ * be run on any location.
+ */
+ default String[] preferredLocations() {
--- End diff --
hmmm, do you mean create a `Host` class which only has a string field?
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