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Giraph examples (for learning and testing)
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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.giraph.examples;

import org.apache.giraph.edge.Edge;
import org.apache.giraph.edge.EdgeFactory;
import org.apache.giraph.graph.BasicComputation;
import org.apache.giraph.graph.Vertex;
import org.apache.giraph.io.VertexReader;
import org.apache.giraph.io.formats.GeneratedVertexInputFormat;
import org.apache.giraph.io.formats.TextVertexOutputFormat;
import org.apache.hadoop.io.FloatWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.log4j.Logger;

import com.google.common.collect.Lists;

import java.io.IOException;
import java.util.List;

/**
 * Just a simple Vertex compute implementation that executes 3 supersteps, then
 * finishes.
 */
public class SimpleSuperstepComputation extends BasicComputation {
  @Override
  public void compute(
      Vertex vertex,
      Iterable messages) throws IOException {
    // Some checks for additional testing
    if (getTotalNumVertices() < 1) {
      throw new IllegalStateException("compute: Illegal total vertices " +
          getTotalNumVertices());
    }
    if (getTotalNumEdges() < 0) {
      throw new IllegalStateException("compute: Illegal total edges " +
          getTotalNumEdges());
    }
    if (vertex.isHalted()) {
      throw new IllegalStateException("compute: Impossible to be halted - " +
          vertex.isHalted());
    }

    if (getSuperstep() > 3) {
      vertex.voteToHalt();
    }
  }

  /**
   * Simple VertexReader that supports {@link SimpleSuperstepComputation}
   */
  public static class SimpleSuperstepVertexReader extends
      GeneratedVertexReader {
    /** Class logger */
    private static final Logger LOG =
        Logger.getLogger(SimpleSuperstepVertexReader.class);

    @Override
    public boolean nextVertex() throws IOException, InterruptedException {
      return totalRecords > recordsRead;
    }

    @Override
    public Vertex getCurrentVertex()
      throws IOException, InterruptedException {
      Vertex vertex =
          getConf().createVertex();
      long tmpId = reverseIdOrder ?
          ((inputSplit.getSplitIndex() + 1) * totalRecords) -
          recordsRead - 1 :
            (inputSplit.getSplitIndex() * totalRecords) + recordsRead;
      LongWritable vertexId = new LongWritable(tmpId);
      IntWritable vertexValue =
          new IntWritable((int) (vertexId.get() * 10));
      List> edges = Lists.newLinkedList();
      long targetVertexId =
          (vertexId.get() + 1) %
          (inputSplit.getNumSplits() * totalRecords);
      float edgeValue = vertexId.get() * 100f;
      edges.add(EdgeFactory.create(new LongWritable(targetVertexId),
          new FloatWritable(edgeValue)));
      vertex.initialize(vertexId, vertexValue, edges);
      ++recordsRead;
      if (LOG.isInfoEnabled()) {
        LOG.info("next: Return vertexId=" + vertex.getId().get() +
            ", vertexValue=" + vertex.getValue() +
            ", targetVertexId=" + targetVertexId +
            ", edgeValue=" + edgeValue);
      }
      return vertex;
    }
  }

  /**
   * Simple VertexInputFormat that supports {@link SimpleSuperstepComputation}
   */
  public static class SimpleSuperstepVertexInputFormat extends
    GeneratedVertexInputFormat {
    @Override
    public VertexReader
    createVertexReader(InputSplit split, TaskAttemptContext context)
      throws IOException {
      return new SimpleSuperstepVertexReader();
    }
  }


  /**
   * Simple VertexOutputFormat that supports {@link SimpleSuperstepComputation}
   */
  public static class SimpleSuperstepVertexOutputFormat extends
      TextVertexOutputFormat {
    @Override
    public TextVertexWriter createVertexWriter(TaskAttemptContext context)
      throws IOException, InterruptedException {
      return new SimpleSuperstepVertexWriter();
    }

    /**
     * Simple VertexWriter that supports {@link SimpleSuperstepComputation}
     */
    public class SimpleSuperstepVertexWriter extends TextVertexWriter {
      @Override
      public void writeVertex(Vertex vertex) throws IOException, InterruptedException {
        getRecordWriter().write(
            new Text(vertex.getId().toString()),
            new Text(vertex.getValue().toString()));
      }
    }
  }
}