Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/16758#discussion_r98794869
--- Diff: sql/core/src/main/scala/org/apache/spark/sql/State.scala ---
@@ -0,0 +1,101 @@
+/*
+ * 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
+
+import org.apache.spark.annotation.{Experimental, InterfaceStability}
+import org.apache.spark.sql.catalyst.plans.logical.LogicalState
+
+/**
+ * :: Experimental ::
+ *
+ * Wrapper class for interacting with state data in `mapGroupsWithState`
and
+ * `flatMapGroupsWithState` operations on
+ * [[org.apache.spark.sql.KeyValueGroupedDataset KeyValueGroupedDataset]].
+ *
+ * @note Operations on state are not threadsafe.
+ *
+ * Scala example of using `State`:
+ * {{{
+ * // A mapping function that maintains an integer state for string
keys and returns a string.
+ * def mappingFunction(key: String, value: Iterable[Int], state:
State[Int]): Option[String] = {
+ * // Check if state exists
+ * if (state.exists) {
+ * val existingState = state.get // Get the existing state
+ * val shouldRemove = ... // Decide whether to remove the
state
+ * if (shouldRemove) {
+ * state.remove() // Remove the state
+ * } else {
+ * val newState = ...
+ * state.update(newState) // Set the new state
+ * }
+ * } else {
+ * val initialState = ...
+ * state.update(initialState) // Set the initial state
+ * }
+ * ... // return something
+ * }
+ *
+ * }}}
+ *
+ * Java example of using `State`:
+ * {{{
+ * // A mapping function that maintains an integer state for string
keys and returns a string.
+ * Function3<String, Iterable<Integer>, State<Integer>, String>
mappingFunction =
+ * new Function3<String, Iterable<Integer>, State<Integer>,
String>() {
+ *
+ * @Override
+ * public String call(String key, Optional<Integer> value,
State<Integer> state) {
+ * if (state.exists()) {
+ * int existingState = state.get(); // Get the existing state
+ * boolean shouldRemove = ...; // Decide whether to remove the
state
+ * if (shouldRemove) {
+ * state.remove(); // Remove the state
+ * } else {
+ * int newState = ...;
+ * state.update(newState); // Set the new state
+ * }
+ * } else {
+ * int initialState = ...; // Set the initial state
+ * state.update(initialState);
+ * }
+ * ... // return something
+ * }
+ * };
+ * }}}
+ *
+ * @tparam S Type of the state
+ * @since 2.1.1
+ */
+@Experimental
+@InterfaceStability.Evolving
+trait State[S] extends LogicalState[S] {
--- End diff --
Agreed.
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