| /* |
| * 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.flink.api.common.functions; |
| |
| import java.io.Serializable; |
| |
| import org.apache.flink.annotation.Public; |
| import org.apache.flink.util.Collector; |
| |
| /** |
| * Generic interface used for combine functions ("combiners"). Combiners act as auxiliaries to a {@link GroupReduceFunction} |
| * and "pre-reduce" the data. The combine functions typically do not see the entire group of elements, but |
| * only a sub-group. |
| * <p> |
| * Combine functions are frequently helpful in increasing the program efficiency, because they allow the system to |
| * reduce the data volume earlier, before the entire groups have been collected. |
| * <p> |
| * This special variant of the combine function supports to return more than one element per group. |
| * It is frequently less efficient to use than the {@link CombineFunction}. |
| * |
| * @param <IN> The data type processed by the combine function. |
| * @param <OUT> The data type emitted by the combine function. |
| */ |
| @Public |
| public interface GroupCombineFunction<IN, OUT> extends Function, Serializable { |
| |
| /** |
| * The combine method, called (potentially multiple timed) with subgroups of elements. |
| * |
| * @param values The elements to be combined. |
| * @param out The collector to use to return values from the function. |
| * |
| * @throws Exception The function may throw Exceptions, which will cause the program to cancel, |
| * and may trigger the recovery logic. |
| */ |
| void combine(Iterable<IN> values, Collector<OUT> out) throws Exception; |
| } |