src/main/java/org/apache/giraph/graph/TextAggregatorWriter.java

/*
 * 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.graph;

import java.io.IOException;
import java.util.Map;
import java.util.Map.Entry;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapreduce.Mapper.Context;

/**
 * Default implementation of {@link AggregatorWriter}. Each line consists of 
 * text and contains the aggregator name, the aggregator value and the 
 * aggregator class.
 */
public class TextAggregatorWriter 
        implements AggregatorWriter {
    /** The filename of the outputfile */
    public static final String FILENAME = 
        "giraph.textAggregatorWriter.filename";
    /** The frequency of writing:
     *  - NEVER: never write, files aren't created at all
     *  - AT_THE_END: aggregators are written only when the computation is over
     *  - int: i.e. 1 is every superstep, 2 every two supersteps and so on 
     */
    public static final String FREQUENCY = 
        "giraph.textAggregatorWriter.frequency";
    private static final String DEFAULT_FILENAME = "aggregatorValues";
    /** Signal for "never write" frequency */
    public static final int NEVER = 0;
    /** Signal for "write only the final values" frequency */
    public static final int AT_THE_END = -1;
    /** Handle to the outputfile */
    protected FSDataOutputStream output;
    private int frequency;
    
    @Override
    @SuppressWarnings("rawtypes")
    public void initialize(Context context, long attempt) throws IOException {
        Configuration conf = context.getConfiguration();
        frequency = conf.getInt(FREQUENCY, NEVER);
        String filename  = conf.get(FILENAME, DEFAULT_FILENAME);
        if (frequency != NEVER) {
            Path p = new Path(filename+"_"+attempt);
            FileSystem fs = FileSystem.get(conf);
            if (fs.exists(p)) {
                throw new RuntimeException("aggregatorWriter file already" +
                    " exists: " + p.getName());
            }
            output = fs.create(p);
        }
    }

    @Override
    final public void writeAggregator(
            Map<String, Aggregator<Writable>> aggregators,
            long superstep) throws IOException {
        
        if (shouldWrite(superstep)) {
            for (Entry<String, Aggregator<Writable>> a: 
                    aggregators.entrySet()) {
                output.writeUTF(aggregatorToString(a.getKey(), 
                                                   a.getValue(), 
                                                   superstep));
            }
            output.flush();
        }
    }
    
    /**
     * Implements the way an aggregator is converted into a String.
     * Override this if you want to implement your own text format.
     * 
     * @param aggregatorName Name of the aggregator
     * @param a Aggregator
     * @param superstep Current superstep
     * @return The String representation for the aggregator
     */
    protected String aggregatorToString(String aggregatorName, 
                                        Aggregator<Writable> a,
                                        long superstep) {

        return new StringBuilder("superstep=").append(superstep).append("\t")
            .append(aggregatorName).append("=").append(a.getAggregatedValue())
            .append("\t").append(a.getClass().getCanonicalName()).append("\n")
            .toString();
    }

    private boolean shouldWrite(long superstep) {
        return ((frequency == AT_THE_END && superstep == LAST_SUPERSTEP) ||
                (frequency != NEVER && superstep % frequency == 0));
    }

    @Override
    public void close() throws IOException {
        if (output != null) {
            output.close();
        }
    }
}