/*

  * 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.comm.aggregators;

 import java.util.AbstractMap;

 import java.util.Map;

 import java.util.Set;

 import java.util.concurrent.ConcurrentMap;

 import org.apache.giraph.reducers.ReduceOperation;

 import org.apache.giraph.reducers.Reducer;

 import org.apache.giraph.utils.TaskIdsPermitsBarrier;

 import org.apache.hadoop.io.Writable;

 import org.apache.hadoop.util.Progressable;

 import org.apache.log4j.Logger;

 import com.google.common.base.Function;

 import com.google.common.collect.Iterables;

 import com.google.common.collect.Maps;

 /**

  * Class for holding aggregators which current worker owns,

  * and aggregating partial aggregator values from workers.

  *

  * Protocol:

  * 1. Before the beginning of superstep, worker receives its aggregators

  * from master, and these aggregators will be registered to this class.

  * Multiple registrations can be called concurrently.

  * 2. During the superstep, whenever a worker finishes computation,

  * it will send partial aggregated values to worker owner. This class is used

  * to help deserialize the arriving aggregator values, and aggregate the values

  * at the destination owner worker; these can happen concurrently.

  * (we know step 1. is finished before anything from step 2. happens because

  * other workers can't start computation before they receive aggregators

  * which this worker owns)

  * 3. This class also tracks the number of partial aggregator requests which

  * worker received. In the end of superstep, getMyAggregatorValuesWhenReady

  * will be called to ensure everything was received and get the values which

  * need to be sent to master.

  * Because of this counting, in step 2. even if worker owns no aggregators,

  * it will still send a message without aggregator data.

  * 4. In the end we reset to prepare for the next superstep.

  */

 public class OwnerAggregatorServerData {

   /** Class logger */

   private static final Logger LOG =

       Logger.getLogger(OwnerAggregatorServerData.class);

   /** Map of aggregators which current worker owns */

   private final ConcurrentMap<String, Reducer<Object, Writable>>

   myReducerMap = Maps.newConcurrentMap();

   /**

    * Counts the requests with partial aggregated values from other workers.

    * It uses GlobalCommType.SPECIAL_COUNT to know how many requests it

    * has to receive.

    */

   private final TaskIdsPermitsBarrier workersBarrier;

   /** Progressable used to report progress */

   private final Progressable progressable;

   /**

    * Constructor

    *

    * @param progressable Progressable used to report progress

    */

   public OwnerAggregatorServerData(Progressable progressable) {

     this.progressable = progressable;

     workersBarrier = new TaskIdsPermitsBarrier(progressable);

   }

   /**

    * Register a reducer which current worker owns. Thread-safe.

    *

    * @param name Name of aggregator

    * @param reduceOp Reduce operation

    */

   public void registerReducer(String name,

       ReduceOperation<Object, Writable> reduceOp) {

     if (LOG.isDebugEnabled() && myReducerMap.isEmpty()) {

       LOG.debug("registerAggregator: The first registration after a reset()");

     }

     myReducerMap.putIfAbsent(name, new Reducer<>(reduceOp));

     progressable.progress();

   }

   /**

    * Reduce partial value of one of current worker's reducers.

    *

    * Thread-safe. Call only after reducers have been registered.

    *

    * @param name Name of the reducer

    * @param value Value to reduce to it

    */

   public void reduce(String name, Writable value) {

     Reducer<Object, Writable> reducer = myReducerMap.get(name);

     synchronized (reducer) {

       reducer.reduceMerge(value);

     }

     progressable.progress();

   }

   /**

    * Create initial value for a reducer. Used so requests

    * would be able to deserialize data.

    *

    * Thread-safe. Call only after reducer has been registered.

    *

    * @param name Name of the reducer

    * @return Empty value

    */

   public Writable createInitialValue(String name) {

     Reducer<Object, Writable> reducer = myReducerMap.get(name);

     synchronized (reducer) {

       return reducer.createInitialValue();

     }

   }

   /**

    * Notify this object that a partial aggregated values request from some

    * worker have been received. Thread-safe.

    */

   public void receivedRequestFromWorker() {

     workersBarrier.releaseOnePermit();

   }

   /**

    * Notify this object about the total number of requests which should

    * arrive from one of the workers. Thread-safe.

    *

    * @param requestCount Number of requests which should arrive

    * @param taskId Task id of that worker

    */

   public void receivedRequestCountFromWorker(long requestCount, int taskId) {

     workersBarrier.requirePermits(requestCount, taskId);

   }

   /**

    * This function will wait until all partial aggregated values from all

    * workers are ready and aggregated, and return final aggregated values

    * afterwards.

    *

    * @param workerIds All workers in the job apart from the current one

    * @return Iterable through final aggregated values which this worker owns

    */

   public Iterable<Map.Entry<String, Writable>>

   getMyReducedValuesWhenReady(Set<Integer> workerIds) {

     workersBarrier.waitForRequiredPermits(workerIds);

     if (LOG.isDebugEnabled()) {

       LOG.debug("getMyAggregatorValuesWhenReady: Values ready");

     }

     return Iterables.transform(myReducerMap.entrySet(),

         new Function<Map.Entry<String, Reducer<Object, Writable>>,

             Map.Entry<String, Writable>>() {

           @Override

           public Map.Entry<String, Writable> apply(

               Map.Entry<String, Reducer<Object, Writable>> aggregator) {

             return new AbstractMap.SimpleEntry<String, Writable>(

                 aggregator.getKey(),

                 aggregator.getValue().getCurrentValue());

           }

         });

   }

   /**

    * Prepare for next superstep

    */

   public void reset() {

     myReducerMap.clear();

     if (LOG.isDebugEnabled()) {

       LOG.debug("reset: Ready for next superstep");

     }

   }

 }