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/***********************************************************************************************************************
 * Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
 *
 * Licensed 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 eu.stratosphere.pact.runtime.task;

import java.io.IOException;
import java.util.List;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import eu.stratosphere.api.common.functions.GenericReduce;
import eu.stratosphere.api.common.typeutils.TypeComparator;
import eu.stratosphere.api.common.typeutils.TypeSerializer;
import eu.stratosphere.api.common.typeutils.TypeSerializerFactory;
import eu.stratosphere.core.memory.MemorySegment;
import eu.stratosphere.nephele.services.memorymanager.MemoryManager;
import eu.stratosphere.pact.runtime.sort.FixedLengthRecordSorter;
import eu.stratosphere.pact.runtime.sort.InMemorySorter;
import eu.stratosphere.pact.runtime.sort.NormalizedKeySorter;
import eu.stratosphere.pact.runtime.sort.QuickSort;
import eu.stratosphere.util.Collector;
import eu.stratosphere.util.MutableObjectIterator;

/**
 * Combine operator for Reduce functions, standalone (not chained).
 * Sorts and groups and reduces data, but never spills the sort. May produce multiple
 * partially aggregated groups.
 * 
 * @param  The data type consumed and produced by the combiner.
 */
public class ReduceCombineDriver implements PactDriver, T> {
	
	private static final Log LOG = LogFactory.getLog(ReduceCombineDriver.class);

	/** Fix length records with a length below this threshold will be in-place sorted, if possible. */
	private static final int THRESHOLD_FOR_IN_PLACE_SORTING = 32;
	
	
	private PactTaskContext, T> taskContext;

	private TypeSerializer serializer;

	private TypeComparator comparator;
	
	private GenericReduce reducer;
	
	private Collector output;
	
	
	private MemoryManager memManager;
	
	private InMemorySorter sorter;
	
	private QuickSort sortAlgo = new QuickSort();
	
	
	private boolean running;

	// ------------------------------------------------------------------------

	@Override
	public void setup(PactTaskContext, T> context) {
		this.taskContext = context;
		this.running = true;
	}
	
	@Override
	public int getNumberOfInputs() {
		return 1;
	}

	@Override
	public Class> getStubType() {
		@SuppressWarnings("unchecked")
		final Class> clazz = (Class>) (Class) GenericReduce.class;
		return clazz;
	}

	@Override
	public boolean requiresComparatorOnInput() {
		return true;
	}

	@Override
	public void prepare() throws Exception {
		if (this.taskContext.getTaskConfig().getDriverStrategy() != DriverStrategy.SORTED_PARTIAL_REDUCE) {
			throw new Exception("Invalid strategy " + this.taskContext.getTaskConfig().getDriverStrategy() + " for reduce combiner.");
		}
		
		this.memManager = this.taskContext.getMemoryManager();
		final int numMemoryPages = memManager.computeNumberOfPages(this.taskContext.getTaskConfig().getMemoryDriver());
		
		// instantiate the serializer / comparator
		final TypeSerializerFactory serializerFactory = this.taskContext.getInputSerializer(0);
		this.serializer = serializerFactory.getSerializer();
		this.comparator = this.taskContext.getInputComparator(0);
		this.serializer = serializerFactory.getSerializer();
		this.reducer = this.taskContext.getStub();
		this.output = this.taskContext.getOutputCollector();

		final List memory = this.memManager.allocatePages(this.taskContext.getOwningNepheleTask(), numMemoryPages);

		// instantiate a fix-length in-place sorter, if possible, otherwise the out-of-place sorter
		if (this.comparator.supportsSerializationWithKeyNormalization() &&
			this.serializer.getLength() > 0 && this.serializer.getLength() <= THRESHOLD_FOR_IN_PLACE_SORTING)
		{
			this.sorter = new FixedLengthRecordSorter(this.serializer, this.comparator, memory);
		} else {
			this.sorter = new NormalizedKeySorter(this.serializer, this.comparator.duplicate(), memory);
		}
	}

	@Override
	public void run() throws Exception {
		if (LOG.isDebugEnabled()) {
			LOG.debug("Combiner starting.");
		}
		
		final MutableObjectIterator in = this.taskContext.getInput(0);
		final TypeSerializer serializer = this.serializer;
		
		T value = serializer.createInstance();
		
		while (running && (value = in.next(value)) != null) {
			
			// try writing to the sorter first
			if (this.sorter.write(value)) {
				continue;
			}
	
			// do the actual sorting, combining, and data writing
			sortAndCombine();
			this.sorter.reset();
			
			// write the value again
			if (!this.sorter.write(value)) {
				throw new IOException("Cannot write record to fresh sort buffer. Record too large.");
			}
		}
		
		// sort, combine, and send the final batch
		sortAndCombine();
	}
		
	private void sortAndCombine() throws Exception {
		final InMemorySorter sorter = this.sorter;

		if (!sorter.isEmpty()) {
			this.sortAlgo.sort(sorter);
			
			final TypeSerializer serializer = this.serializer;
			final TypeComparator comparator = this.comparator;
			
			final GenericReduce function = this.reducer;
			
			final Collector output = this.output;
			
			final MutableObjectIterator input = sorter.getIterator();
			
			T value = input.next(serializer.createInstance());
			
			// iterate over key groups
			while (this.running && value != null) {
				comparator.setReference(value);
				T res = value;
				
				// iterate within a key group
				while ((value = input.next(serializer.createInstance())) != null) {
					if (comparator.equalToReference(value)) {
						// same group, reduce
						res = function.reduce(res, value);
					} else {
						// new key group
						break;
					}
				}
				
				output.collect(res);
			}
		}
	}

	@Override
	public void cleanup() {
		this.memManager.release(this.sorter.dispose());
	}

	@Override
	public void cancel() {
		this.running = false;
		this.memManager.release(this.sorter.dispose());
	}
}