heron/api/src/java/org/apache/heron/api/topology/IStatefulComponent.java

/**
 * 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.heron.api.topology;

import java.io.Serializable;

import org.apache.heron.api.state.State;

/**
 * Defines a component that saves its internal state in the State interface
 */
public interface IStatefulComponent<K extends Serializable, V extends Serializable>
                 extends IComponent {

  /**
   * Initializes the state of the function or operator to that of a previous checkpoint.
   * This method is invoked when a component is executed as part of a recovery run. In case
   * there was prior state associated with the component, the state will be empty.
   * Stateful Spouts/Bolts are expected to hold on to the state variable to save their
   * internal state
   * <p>
   * Note that initialState() is called before open() or prepare().
   *
   * @param state the previously saved state of the component.
   */
  void initState(State<K, V> state);

  /**
   * This is a hook for the component to perform some actions just before the
   * framework saves its state.
   *
   * @param checkpointId the ID of the checkpoint
   */
  void preSave(String checkpointId);
}