/*
* 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.tinkerpop.gremlin.spark.process.computer;
import org.apache.tinkerpop.gremlin.process.computer.MapReduce;
import org.apache.tinkerpop.gremlin.process.traversal.util.FastNoSuchElementException;
import scala.Tuple2;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Queue;
/**
* @author Marko A. Rodriguez (http://markorodriguez.com)
*/
public final class ReduceIterator<K, V, OK, OV> implements Iterator<Tuple2<OK, OV>> {
private final Iterator<Tuple2<K, Iterable<V>>> inputIterator;
private final MapReduce<K, V, OK, OV, ?> mapReduce;
private final Queue<Tuple2<OK, OV>> queue = new LinkedList<>();
private final ReduceIteratorEmitter reduceIteratorEmitter = new ReduceIteratorEmitter();
public ReduceIterator(final MapReduce<K, V, OK, OV, ?> mapReduce, final Iterator<Tuple2<K, Iterable<V>>> inputIterator) {
this.inputIterator = inputIterator;
this.mapReduce = mapReduce;
this.mapReduce.workerStart(MapReduce.Stage.REDUCE);
}
@Override
public boolean hasNext() {
if (!this.queue.isEmpty())
return true;
else if (!this.inputIterator.hasNext()) {
this.mapReduce.workerEnd(MapReduce.Stage.REDUCE);
return false;
} else {
this.processNext();
return this.hasNext();
}
}
@Override
public Tuple2<OK, OV> next() {
if (!this.queue.isEmpty())
return this.queue.remove();
else if (!this.inputIterator.hasNext()) {
this.mapReduce.workerEnd(MapReduce.Stage.REDUCE);
throw FastNoSuchElementException.instance();
} else {
this.processNext();
return this.next();
}
}
private void processNext() {
final Tuple2<K, Iterable<V>> nextKeyValues = this.inputIterator.next();
this.mapReduce.reduce(nextKeyValues._1(), nextKeyValues._2().iterator(), this.reduceIteratorEmitter);
}
private class ReduceIteratorEmitter implements MapReduce.ReduceEmitter<OK, OV> {
@Override
public void emit(final OK key, OV value) {
queue.add(new Tuple2<>(key, value));
}
}
}