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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 java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.Charset;
import java.util.Set;

import org.apache.giraph.worker.WorkerContext;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.filecache.DistributedCache;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.log4j.Logger;

import com.google.common.collect.ImmutableSet;

/**
 * Worker context for random walks.
 */
public class RandomWalkWorkerContext extends WorkerContext {
  /** Default maximum number of iterations */
  private static final int DEFAULT_MAX_SUPERSTEPS = 30;
  /** Default teleportation probability */
  private static final float DEFAULT_TELEPORTATION_PROBABILITY = 0.15f;
  /** Maximum number of iterations */
  private static int MAX_SUPERSTEPS;
  /** Teleportation probability */
  private static double TELEPORTATION_PROBABILITY;
  /** Preference vector */
  private static Set SOURCES;

  /** Configuration parameter for the source vertex */
  private static final String SOURCE_VERTEX =
      RandomWalkWithRestartComputation.class.getName() + ".sourceVertex";

  /** Logger */
  private static final Logger LOG = Logger
      .getLogger(RandomWalkWorkerContext.class);

  /**
   * @return The maximum number of iterations to perform.
   */
  public int getMaxSupersteps() {
    if (MAX_SUPERSTEPS == 0) {
      throw new IllegalStateException(
          RandomWalkWorkerContext.class.getSimpleName() +
              " was not initialized. Relaunch your job " +
              "by setting the appropriate WorkerContext");
    }
    return MAX_SUPERSTEPS;
  }

  /**
   * @return The teleportation probability.
   */
  public double getTeleportationProbability() {
    if (TELEPORTATION_PROBABILITY == 0) {
      throw new IllegalStateException(
          RandomWalkWorkerContext.class.getSimpleName() +
              " was not initialized. Relaunch your job " +
              "by setting the appropriate WorkerContext");
    }
    return TELEPORTATION_PROBABILITY;
  }

  /**
   * Checks if a vertex is a source.
   * @param id The vertex ID to check.
   * @return True if the vertex is a source in the preference vector.
   */
  public boolean isSource(long id) {
    return SOURCES.contains(id);
  }

  /**
   * @return The number of sources in the preference vector.
   */
  public int numSources() {
    return SOURCES.size();
  }

  /**
   * Initialize sources for Random Walk with Restart. First option
   * (preferential) is single source given from the command line as a parameter.
   * Second option is a file with a list of vertex IDs, one per line. In this
   * second case the preference vector is a uniform distribution over these
   * vertexes.
   * @param configuration The configuration.
   * @return a (possibly empty) set of source vertices
   */
  private ImmutableSet initializeSources(Configuration configuration) {
    ImmutableSet.Builder builder = ImmutableSet.builder();
    long sourceVertex = configuration.getLong(SOURCE_VERTEX, Long.MIN_VALUE);
    if (sourceVertex != Long.MIN_VALUE) {
      return ImmutableSet.of(sourceVertex);
    } else {
      Path sourceFile = null;
      try {

        Path[] cacheFiles = DistributedCache.getLocalCacheFiles(configuration);
        if (cacheFiles == null || cacheFiles.length == 0) {
          // empty set if no source vertices configured
          return ImmutableSet.of();
        }

        sourceFile = cacheFiles[0];
        FileSystem fs = FileSystem.getLocal(configuration);
        BufferedReader in = new BufferedReader(new InputStreamReader(
            fs.open(sourceFile), Charset.defaultCharset()));
        String line;
        while ((line = in.readLine()) != null) {
          builder.add(Long.parseLong(line));
        }
        in.close();
      } catch (IOException e) {
        getContext().setStatus(
            "Could not load local cache files: " + sourceFile);
        LOG.error("Could not load local cache files: " + sourceFile, e);
      }
    }
    return builder.build();
  }

  @Override
  public void preApplication() throws InstantiationException,
      IllegalAccessException {
    setStaticVars(getContext().getConfiguration());
  }

  /**
   * Set static variables from Configuration
   *
   * @param configuration the conf
   */
  private void setStaticVars(Configuration configuration) {
    MAX_SUPERSTEPS = configuration.getInt(RandomWalkComputation.MAX_SUPERSTEPS,
        DEFAULT_MAX_SUPERSTEPS);
    TELEPORTATION_PROBABILITY = configuration.getFloat(
        RandomWalkComputation.TELEPORTATION_PROBABILITY,
        DEFAULT_TELEPORTATION_PROBABILITY);
    SOURCES = initializeSources(configuration);
  }

  @Override
  public void preSuperstep() {
  }

  @Override
  public void postSuperstep() {
  }

  @Override
  public void postApplication() {
  }
}