/*
* 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.lucene.search;
import java.io.IOException;
import java.util.Collection;
/**
* A manager of collectors. This class is useful to parallelize execution of
* search requests and has two main methods:
* <ul>
* <li>{@link #newCollector()} which must return a NEW collector which
* will be used to collect a certain set of leaves.</li>
* <li>{@link #reduce(Collection)} which will be used to reduce the
* results of individual collections into a meaningful result.
* This method is only called after all leaves have been fully
* collected.</li>
* </ul>
*
* @see IndexSearcher#search(Query, CollectorManager)
* @lucene.experimental
*/
public interface CollectorManager<C extends Collector, T> {
/**
* Return a new {@link Collector}. This must return a different instance on
* each call.
*/
C newCollector() throws IOException;
/**
* Reduce the results of individual collectors into a meaningful result.
* For instance a {@link TopDocsCollector} would compute the
* {@link TopDocsCollector#topDocs() top docs} of each collector and then
* merge them using {@link TopDocs#merge(int, TopDocs[])}.
* This method must be called after collection is finished on all provided
* collectors.
*/
T reduce(Collection<C> collectors) throws IOException;
}