content: /**
   * 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.atlas.listener;
  
  import org.apache.atlas.AtlasException;
  
  /**
   * An interface that should be implemented by objects and services to react to changes in state of an Atlas server.
   *
   * The two state transitions we handle are (1) becoming active and (2) becoming passive.
   */
  public interface ActiveStateChangeHandler {
      enum HandlerOrder {
          AUDIT_REPOSITORY(0),
          GRAPH_BACKED_SEARCH_INDEXER(1),
          TYPEDEF_STORE_INITIALIZER(2),
          ATLAS_PATCH_SERVICE(3),
          DEFAULT_METADATA_SERVICE(4),
          NOTIFICATION_HOOK_CONSUMER(5),
          TASK_MANAGEMENT(6),
          INDEX_RECOVERY(7),
          IMPORT_TASK_LISTENER(8);
  
          private final int order;
  
          HandlerOrder(int order) {
              this.order = order;
          }
  
          public int getOrder() {
              return order;
          }
      }
  
      /**
       * Callback that is invoked on an implementor when this instance of Atlas server is declared the leader.
       *
       * Any initialization that must be carried out by an implementor only when the server becomes active
       * should happen on this callback.
       *
       * @throws {@link AtlasException} if anything is wrong on initialization
       */
      void instanceIsActive() throws AtlasException;
  
      /**
       * Callback that is invoked on an implementor when this instance of Atlas server is removed as the leader.
       *
       * Any cleanup that must be carried out by an implementor when the server becomes passive
       * should happen on this callback.
       *
       * @throws {@link AtlasException} if anything is wrong on shutdown
       */
  
      void instanceIsPassive() throws AtlasException;
  
      /**
       * Defines the order in which the handler should be called.
       *   When state becomes active, the handler will be called from low order to high
       *   When state becomes passive, the handler will be called from high order to low
       */
      int getHandlerOrder();
  }
  