spark State 源码

spark State 代码

文件路径：/streaming/src/main/scala/org/apache/spark/streaming/State.scala

/*
 * 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 org.apache.spark.annotation.Experimental

/**
 * :: Experimental ::
 * Abstract class for getting and updating the state in mapping function used in the `mapWithState`
 * 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`:
 * {{{
 *    // A mapping function that maintains an integer state and returns a String
 *    def mappingFunction(key: String, value: Option[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 and returns a String
 *    Function3<String, Optional<Integer>, State<Integer>, String> mappingFunction =
 *       new Function3<String, Optional<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 Class of the state
 */
@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 timeout 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 a `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>")
  }
}

/** Internal implementation of the [[State]] interface */
private[streaming] class StateImpl[S] extends State[S] {

  private var state: S = null.asInstanceOf[S]
  private var defined: Boolean = false
  private var timingOut: Boolean = false
  private var updated: Boolean = false
  private var removed: Boolean = false

  // ========= Public API =========
  override def exists(): Boolean = {
    defined
  }

  override def get(): S = {
    if (defined) {
      state
    } else {
      throw new NoSuchElementException("State is not set")
    }
  }

  override def update(newState: S): Unit = {
    require(!removed, "Cannot update the state after it has been removed")
    require(!timingOut, "Cannot update the state that is timing out")
    state = newState
    defined = true
    updated = true
  }

  override def isTimingOut(): Boolean = {
    timingOut
  }

  override def remove(): Unit = {
    require(!timingOut, "Cannot remove the state that is timing out")
    require(!removed, "Cannot remove the state that has already been removed")
    defined = false
    updated = false
    removed = true
  }

  // ========= Internal API =========

  /** Whether the state has been marked for removing */
  def isRemoved(): Boolean = {
    removed
  }

  /** Whether the state has been updated */
  def isUpdated(): Boolean = {
    updated
  }

  /**
   * Update the internal data and flags in `this` to the given state option.
   * This method allows `this` object to be reused across many state records.
   */
  def wrap(optionalState: Option[S]): Unit = {
    optionalState match {
      case Some(newState) =>
        this.state = newState
        defined = true

      case None =>
        this.state = null.asInstanceOf[S]
        defined = false
    }
    timingOut = false
    removed = false
    updated = false
  }

  /**
   * Update the internal data and flags in `this` to the given state that is going to be timed out.
   * This method allows `this` object to be reused across many state records.
   */
  def wrapTimingOutState(newState: S): Unit = {
    this.state = newState
    defined = true
    timingOut = true
    removed = false
    updated = false
  }
}

相关信息

spark 源码目录

相关文章

spark Checkpoint 源码

spark ContextWaiter 源码

spark DStreamGraph 源码

spark Duration 源码

spark Interval 源码

spark StateSpec 源码

spark StreamingConf 源码

spark StreamingContext 源码

spark StreamingSource 源码

spark Time 源码