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Apache Solr (module: core)
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/*
 * 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.solr.core;

/**
 * Used to request notification when the core is closed.
 *
 * Call {@link org.apache.solr.core.SolrCore#addCloseHook(org.apache.solr.core.CloseHook)} during
 * the {@link org.apache.solr.util.plugin.SolrCoreAware#inform(SolrCore)} method to add a close hook
 * to your object.
 *
 * 
The close hook can be useful for releasing objects related to the request handler (for
 * instance, if you have a JDBC DataSource or something like that)
 */
public interface CloseHook {

  /**
   * Method called when the given SolrCore object is closing / shutting down but before the update
   * handler and searcher(s) are actually closed 

   * Important: Keep the method implementation as short as possible. If it were to use any
   * heavy i/o , network connections - it might be a better idea to launch in a separate Thread so
   * as to not block the process of shutting down a given SolrCore instance.
   *
   * @param core SolrCore object that is shutting down / closing
   */
  default void preClose(SolrCore core) {}

  /**
   * Method called when the given SolrCore object has been shut down and update handlers and
   * searchers are closed 

   * Use this method for post-close clean up operations e.g. deleting the index from disk. 

   * The core's passed to the method is already closed and therefore, its update handler or
   * searcher should *NOT* be used
   *
   * Important: Keep the method implementation as short as possible. If it were to use any
   * heavy i/o , network connections - it might be a better idea to launch in a separate Thread so
   * as to not block the process of shutting down a given SolrCore instance.
   *
   * @param core SolrCore object that is shutting down / closing
   */
  default void postClose(SolrCore core) {}
}