/*

  * 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.aggregators.DoubleSumAggregator;

 import org.apache.giraph.aggregators.LongSumAggregator;

 import org.apache.giraph.master.DefaultMasterCompute;

 import org.apache.hadoop.io.DoubleWritable;

 import org.apache.hadoop.io.LongWritable;

 import org.apache.log4j.Logger;

 /**

  * Master compute associated with {@link RandomWalkComputation}. It handles

  * dangling nodes.

  */

 public class RandomWalkVertexMasterCompute extends DefaultMasterCompute {

   /** threshold for the L1 norm of the state vector difference  */

   static final double CONVERGENCE_THRESHOLD = 0.00001;

   /** logger */

   private static final Logger LOG =

       Logger.getLogger(RandomWalkVertexMasterCompute.class);

   @Override

   public void compute() {

     double danglingContribution =

         this.<DoubleWritable>getAggregatedValue(

             RandomWalkComputation.CUMULATIVE_DANGLING_PROBABILITY).get();

     double cumulativeProbability =

         this.<DoubleWritable>getAggregatedValue(

             RandomWalkComputation.CUMULATIVE_PROBABILITY).get();

     double l1NormOfStateDiff =

         this.<DoubleWritable>getAggregatedValue(

             RandomWalkComputation.L1_NORM_OF_PROBABILITY_DIFFERENCE).get();

     long numDanglingVertices =

         this.<LongWritable>getAggregatedValue(

             RandomWalkComputation.NUM_DANGLING_VERTICES).get();

     LOG.info("[Superstep " + getSuperstep() + "] Dangling contribution = " +

         danglingContribution + ", number of dangling vertices = " +

         numDanglingVertices + ", cumulative probability = " +

         cumulativeProbability + ", L1 Norm of state vector difference = " +

         l1NormOfStateDiff);

     // Convergence check: halt once the L1 norm of the difference between the

     // state vectors fall below the threshold

     if (getSuperstep() > 1 && l1NormOfStateDiff < CONVERGENCE_THRESHOLD) {

       haltComputation();

     }

   }

   @Override

   public void initialize() throws InstantiationException,

       IllegalAccessException {

     registerAggregator(RandomWalkComputation.NUM_DANGLING_VERTICES,

         LongSumAggregator.class);

     registerAggregator(RandomWalkComputation.CUMULATIVE_DANGLING_PROBABILITY,

         DoubleSumAggregator.class);

     registerAggregator(RandomWalkComputation.CUMULATIVE_PROBABILITY,

         DoubleSumAggregator.class);

     registerAggregator(RandomWalkComputation.L1_NORM_OF_PROBABILITY_DIFFERENCE,

         DoubleSumAggregator.class);

   }

 }