Github user squito commented on a diff in the pull request:
https://github.com/apache/spark/pull/17902#discussion_r119408662
--- Diff:
common/kvstore/src/main/java/org/apache/spark/kvstore/KVStoreView.java ---
@@ -0,0 +1,126 @@
+/*
+ * 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.kvstore;
+
+import java.util.Iterator;
+import java.util.Map;
+
+import com.google.common.base.Preconditions;
+
+/**
+ * A configurable view that allows iterating over values in a {@link
KVStore}.
+ *
+ * <p>
+ * The different methods can be used to configure the behavior of the
iterator. Calling the same
+ * method multiple times is allowed; the most recent value will be used.
+ * </p>
+ *
+ * <p>
+ * The iterators returns by this view are of type {@link KVStoreIterator};
they auto-close
+ * when used in a for loop that exhausts their contents, but when used
manually, they need
+ * to be closed explicitly unless all elements are read.
+ * </p>
+ */
+public abstract class KVStoreView<T> implements Iterable<T> {
+
+ final Class<T> type;
+
+ boolean ascending = true;
+ String index = KVIndex.NATURAL_INDEX_NAME;
+ Object first = null;
+ Object last = null;
+ Object parent = null;
+ long skip = 0L;
+ long max = Long.MAX_VALUE;
+
+ public KVStoreView(Class<T> type) {
+ this.type = type;
+ }
+
+ /**
+ * Reverses the order of iteration. By default, iterates in ascending
order.
+ */
+ public KVStoreView<T> reverse() {
+ ascending = !ascending;
+ return this;
+ }
+
+ /**
+ * Iterates according to the given index.
+ */
+ public KVStoreView<T> index(String name) {
+ this.index = Preconditions.checkNotNull(name);
+ return this;
+ }
+
+ /**
+ * Defines the value of the parent index when iterating over a child
index. Only elements that
+ * match the parent index's value will be included in the iteration.
+ *
+ * <p>
+ * Required for iterating over child indices, will generate an error if
iterating over a
+ * parent-less index.
+ * </p>
+ */
+ public KVStoreView<T> parent(Object value) {
+ this.parent = value;
+ return this;
+ }
+
+ /**
+ * Iterates starting at the given value of the chosen index.
+ */
+ public KVStoreView<T> first(Object value) {
+ this.first = value;
+ return this;
+ }
+
+ /**
+ * Stops iteration at the given value of the chosen index.
--- End diff --
would be nice to clarify whether the matching element is included or not.
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