bookExamples.ch4.algorithms.SimpleShortestPathsComputation.java Source code

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Here is the source code for bookExamples.ch4.algorithms.SimpleShortestPathsComputation.java

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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 bookExamples.ch4.algorithms;

import org.apache.giraph.Algorithm;
import org.apache.giraph.graph.BasicComputation;
import org.apache.giraph.conf.LongConfOption;
import org.apache.giraph.edge.Edge;
import org.apache.giraph.graph.Vertex;
import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.FloatWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.log4j.Logger;

import java.io.IOException;

/**
 * Demonstrates the basic Pregel shortest paths implementation.
 */
@Algorithm(name = "Shortest paths", description = "Finds all shortest paths from a selected vertex")
public class SimpleShortestPathsComputation
        extends BasicComputation<LongWritable, DoubleWritable, FloatWritable, DoubleWritable> {
    /** The shortest paths id */
    public static final LongConfOption SOURCE_ID = new LongConfOption("SimpleShortestPathsVertex.sourceId", 1,
            "The shortest paths id");
    /** Class logger */
    private static final Logger LOG = Logger.getLogger(SimpleShortestPathsComputation.class);

    /**
     * Is this vertex the source id?
     *
     * @param vertex Vertex
     * @return True if the source id
     */
    private boolean isSource(Vertex<LongWritable, ?, ?> vertex) {
        return vertex.getId().get() == SOURCE_ID.get(getConf());
    }

    @Override
    public void compute(Vertex<LongWritable, DoubleWritable, FloatWritable> vertex,
            Iterable<DoubleWritable> messages) throws IOException {
        if (getSuperstep() == 0) {
            vertex.setValue(new DoubleWritable(Double.MAX_VALUE));
        }
        double minDist = isSource(vertex) ? 0d : Double.MAX_VALUE;
        for (DoubleWritable message : messages) {
            minDist = Math.min(minDist, message.get());
        }
        if (LOG.isDebugEnabled()) {
            LOG.debug("Vertex " + vertex.getId() + " got minDist = " + minDist + " vertex value = "
                    + vertex.getValue());
        }
        if (minDist < vertex.getValue().get()) {
            vertex.setValue(new DoubleWritable(minDist));
            for (Edge<LongWritable, FloatWritable> edge : vertex.getEdges()) {
                double distance = minDist + edge.getValue().get();
                if (LOG.isDebugEnabled()) {
                    LOG.debug(
                            "Vertex " + vertex.getId() + " sent to " + edge.getTargetVertexId() + " = " + distance);
                }
                sendMessage(edge.getTargetVertexId(), new DoubleWritable(distance));
            }
        }
        vertex.voteToHalt();
    }
}