api/src/main/java/com/datatorrent/api/annotation/Stateless.java

/**
 * Copyright (C) 2015 DataTorrent, Inc.
 *
 * Licensed 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 com.datatorrent.api.annotation;

import java.lang.annotation.*;

/**
 * When a class or interface is annotated with this annotation, the object which are
 * instanceof such a class or interface are assumed to have the same serialized state
 * it attains after it's configured completely.
 *
 * This annotation is typically is used to mark the operator Stateless. That means
 * the checkpointing for such an operator will be skipped. In case of failure the
 * serialized instance of the operator which was submitted to the DAG will be used to
 * reinstantiate it and used to recover the application from the assumed checkpoint
 * onwards.
 *
 * @since 0.9.4
 */
@Documented
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Stateless
{
  /**
   * WindowId of the unaltered state of an operator.
   * The first windowId during which data may be given to the operator is zero.
   */
  long WINDOW_ID = -1;
}