Github user mateiz commented on a diff in the pull request:
https://github.com/apache/spark/pull/9256#discussion_r44213890
--- Diff: streaming/src/main/scala/org/apache/spark/streaming/State.scala
---
@@ -0,0 +1,199 @@
+/*
+ * 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.streaming
+
+import scala.language.implicitConversions
+
+import org.apache.spark.annotation.Experimental
+
+/**
+ * :: Experimental ::
+ * Abstract class for getting and updating the tracked state in the
`trackStateByKey` operation of
+ * a [[org.apache.spark.streaming.dstream.PairDStreamFunctions pair
DStream]] (Scala) or a
+ * [[org.apache.spark.streaming.api.java.JavaPairDStream JavaPairDStream]]
(Java).
+ *
+ * Scala example of using `State`:
+ * {{{
+ * def trackStateFunc(key: String, data: Option[Int], wrappedState:
State[Int]): Option[Int] = {
+ *
+ * // Check if state exists
+ * if (state.exists) {
+ *
+ * val existingState = wrappedState.get // Get the existing state
+ *
+ * val shouldRemove = ... // Decide whether to remove the state
+ *
+ * if (shouldRemove) {
+ *
+ * wrappedState.remove() // Remove the state
+ *
+ * } else {
+ *
+ * val newState = ...
+ * wrappedState(newState) // Set the new state
+ *
+ * }
+ * } else {
+ *
+ * val initialState = ...
+ * state.update(initialState) // Set the initial state
+ *
+ * }
+ * }
+ *
+ * }}}
+ *
+ * Java example:
+ * {{{
+ * TODO(@zsxwing)
+ * }}}
+ */
+@Experimental
+sealed abstract class State[S] {
+
+ /** Whether the state already exists */
+ def exists(): Boolean
+
+ /**
+ * Get the state if it exists, otherwise it will throw
`java.util.NoSuchElementException`.
+ * Check with `exists()` whether the state exists or not before calling
`get()`.
+ *
+ * @throws java.util.NoSuchElementException If the state does not exist.
+ */
+ def get(): S
+
+ /**
+ * Update the state with a new value.
+ *
+ * State cannot be updated if it has been already removed (that is,
`remove()` has already been
+ * called) or it is going to be removed due to timeout (that is,
`isTimingOut()` is `true`).
+ *
+ * @throws java.lang.IllegalArgumentException If the state has already
been removed, or is
+ * going to be removed
+ */
+ def update(newState: S): Unit
+
+ /**
+ * Remove the state if it exists.
+ *
+ * State cannot be updated if it has been already removed (that is,
`remove()` has already been
+ * called) or it is going to be removed due to timeout (that is,
`isTimingOut()` is `true`).
+ */
+ def remove(): Unit
+
+ /**
+ * Whether the state is timing out and going to be removed by the system
after the current batch.
+ * This timeou can occur if timeout duration has been specified in the
+ * [[org.apache.spark.streaming.StateSpec StatSpec]] and the key has not
received any new data
+ * for that timeout duration.
+ */
+ def isTimingOut(): Boolean
+
+ /**
+ * Get the state as an [[scala.Option]]. It will be `Some(state)` if it
exists, otherwise `None`.
+ */
+ @inline final def getOption(): Option[S] = if (exists) Some(get()) else
None
+
+ @inline final override def toString(): String = {
+ getOption.map { _.toString }.getOrElse("<state not set>")
+ }
+}
+
+private[streaming]
+object State {
+ implicit def toOption[S](state: State[S]): Option[S] = state.getOption()
+}
--- End diff --
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