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 com.aliyun.odps.graph;
  
  import java.io.IOException;
  
  import com.aliyun.odps.conf.Configuration;
  import com.aliyun.odps.io.Writable;
  import com.aliyun.odps.io.WritableComparable;
  
  /**
   * Combiner 对发送给同一个点的消息进行合并，用于减少网络开销和内存占用.
   *
   * <p>
   * Combiner 会被用于发送端和接收端，发送端可以减少消息发送量，接收端可以减少内存占用.
   *
   * @param <I>
   *     Vertex ID 类型
   * @param <M>
   *     Message 类型
   */
  public abstract class Combiner<I extends WritableComparable, M extends Writable> {
  
    /**
     * 此方法会在 Combiner 对象被new出来后立即调用，传入运行时的{@link Configuration}对象
     *
     * @param conf
     *     运行时的 {@link Configuration} 对象
     */
    public void configure(Configuration conf) throws IOException {
    }
  
    /**
     * 将发送给同一个点的多条消息聚集成一条消息.
     *
     * @param vertexId
     *     点的标识
     * @param combinedMessage
     *     合并后的消息
     * @param messageToCombine
     *     将要被合并的消息
     * @throws IOException
     */
    public abstract void combine(I vertexId, M combinedMessage, M messageToCombine)
        throws IOException;
  
  }
  