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 FixedSizeChunkPartitioner} dynamically partitions data into chunks
038 * of a fixed length. The partitioner does not need to know
039 * about the length of the data apriori. 
040 * 
041 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
042 *
043 * @param <T> Type of object in the partition
044 */
045public class FixedSizeChunkPartitioner<T> implements Partitioner<T> {
046        private Iterator<T> objects;
047        private int chunkSize = 20;
048        
049        /**
050         * Construct with data in the form of an {@link Iterable}. The number of
051         * items per chunk is set at the default value (20).
052         * 
053         * @param objects the {@link Iterable} representing the data.
054         */
055        public FixedSizeChunkPartitioner(Iterable<T> objects) {
056                this.objects = objects.iterator();
057        }
058        
059        /**
060         * Construct with data in the form of an {@link Iterable} and the given
061         * number of items per chunk.
062         * 
063         * @param objects the {@link Iterable} representing the data.
064         * @param chunkSize number of items in each chunk.
065         */
066        public FixedSizeChunkPartitioner(Iterable<T> objects, int chunkSize) {
067                this.objects = objects.iterator();
068                this.chunkSize = chunkSize;
069        }
070
071        @Override
072        public Iterator<Iterator<T>> getPartitions() {
073                return new Iterator<Iterator<T>>() {
074
075                        @Override
076                        public boolean hasNext() {
077                                synchronized (objects) {
078                                        return objects.hasNext();
079                                }
080                        }
081
082                        @Override
083                        public Iterator<T> next() {
084                                synchronized (objects) {
085                                        if (!objects.hasNext())
086                                                return null;
087                                        
088                                        List<T> list = new ArrayList<T>(chunkSize);
089                                        
090                                        int i=0;
091                                        while (objects.hasNext() && i<chunkSize) {
092                                                list.add(objects.next());
093                                                i++;
094                                        }
095                                        
096                                        return list.iterator();
097                                }
098                        }
099
100                        @Override
101                        public void remove() {
102                                throw new UnsupportedOperationException("Not supported");
103                        }
104                };
105        }
106}