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;
035import java.util.Queue;
036
037/**
038 * A {@link FixedSizeBlockingChunkPartitioner} dynamically partitions data into
039 * chunks of a fixed length. The partitioner does not need to know about the
040 * length of the data apriori. Beyond a {@link FixedSizeChunkPartitioner} this
041 * implementation doesn't use an underlying iterator. It can only be
042 * instantiated on queues and will always report to have more items available
043 * while it waits for the queue to be filled.
044 * 
045 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
046 * 
047 * @param <T>
048 *            Type of object in the partition
049 */
050public class FixedSizeBlockingChunkPartitioner<T> implements Partitioner<T> {
051        private Queue<T> queue;
052        private int chunkSize = 20;
053
054        /**
055         * Construct with data in the form of a {@link Queue}. The number of items
056         * per chunk is set at the default value (20).
057         * 
058         * @param objects
059         *            the {@link Queue} representing the data.
060         */
061        public FixedSizeBlockingChunkPartitioner(Queue<T> objects) {
062                this.queue = objects;
063        }
064
065        /**
066         * Construct with data in the form of an {@link Queue} and the given number
067         * of items per chunk.
068         * 
069         * @param objects
070         *            the {@link Queue} representing the data.
071         * @param chunkSize
072         *            number of items in each chunk.
073         */
074        public FixedSizeBlockingChunkPartitioner(Queue<T> objects, int chunkSize) {
075                this.queue = objects;
076                this.chunkSize = chunkSize;
077        }
078
079        @Override
080        public Iterator<Iterator<T>> getPartitions() {
081                return new Iterator<Iterator<T>>() {
082
083                        @Override
084                        public boolean hasNext() {
085                                return true;
086                        }
087
088                        @Override
089                        public Iterator<T> next() {
090
091                                final List<T> list = new ArrayList<T>(chunkSize);
092
093                                int i = 0;
094                                while (i < chunkSize) {
095                                        T toAdd = null;
096                                        synchronized (queue) {
097                                                toAdd = queue.poll();
098                                        }
099                                        if (toAdd == null) {
100                                                continue;
101                                        }
102                                        list.add(toAdd);
103                                        i++;
104                                }
105
106                                return list.iterator();
107
108                        }
109
110                        @Override
111                        public void remove() {
112                                throw new UnsupportedOperationException("Not supported");
113                        }
114                };
115        }
116}