001/**
002 * Copyright (c) 2011, The University of Southampton and the individual contributors.
003 * All rights reserved.
004 *
005 * Redistribution and use in source and binary forms, with or without modification,
006 * are permitted provided that the following conditions are met:
007 *
008 *   *  Redistributions of source code must retain the above copyright notice,
009 *      this list of conditions and the following disclaimer.
010 *
011 *   *  Redistributions in binary form must reproduce the above copyright notice,
012 *      this list of conditions and the following disclaimer in the documentation
013 *      and/or other materials provided with the distribution.
014 *
015 *   *  Neither the name of the University of Southampton nor the names of its
016 *      contributors may be used to endorse or promote products derived from this
017 *      software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
020 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
021 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
022 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
023 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
026 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
028 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package org.openimaj.util.parallel.partition;
031
032import java.util.ArrayList;
033import java.util.Iterator;
034import java.util.List;
035
036/**
037 * A {@link GrowingChunkPartitioner} dynamically partitions data into chunks. 
038 * The partitioner does not need to know about the length of the data apriori.
039 * The size of the chunks grows over time exponentially.
040 * 
041 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
042 *
043 * @param <T> Type of object in the partition
044 */
045public class GrowingChunkPartitioner<T> implements Partitioner<T> {
046        private static final int NUM_HW_THREADS = Runtime.getRuntime().availableProcessors();
047        private Iterator<T> objects;
048        
049        /**
050         * Construct with data in the form of an {@link Iterable}. 
051         * 
052         * @param objects the {@link Iterable} representing the data.
053         */
054        public GrowingChunkPartitioner(Iterable<T> objects) {
055                this.objects = objects.iterator();
056        }
057
058        @Override
059        public Iterator<Iterator<T>> getPartitions() {
060                return new Iterator<Iterator<T>>() {
061                        private int currentIteration = 0;
062                        private int chunkSize = 2;
063                        
064                        @Override
065                        public boolean hasNext() {
066                                synchronized (objects) {
067                                        return objects.hasNext();
068                                }
069                        }
070
071                        @Override
072                        public Iterator<T> next() {
073                                synchronized (objects) {
074                                        if (!objects.hasNext())
075                                                return null;
076                                        
077                                        if (currentIteration % NUM_HW_THREADS == 0) {
078                                                chunkSize = (int)Math.pow(2, (currentIteration/NUM_HW_THREADS) + 1);
079                                        }
080                                        
081                                        List<T> list = new ArrayList<T>(chunkSize);
082                                        
083                                        int i=0;
084                                        while (objects.hasNext() && i<chunkSize) {
085                                                list.add(objects.next());
086                                                i++;
087                                        }
088                                        
089                                        currentIteration++;
090                                        return list.iterator();
091                                }
092                        }
093
094                        @Override
095                        public void remove() {
096                                throw new UnsupportedOperationException("Not supported");
097                        }
098                };
099        }
100}