    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.collections4.bloomfilter;
    018
    019import java.util.Arrays;
    020import java.util.Objects;
    021import java.util.function.IntPredicate;
    022import java.util.function.LongPredicate;
    023import java.util.stream.IntStream;
    024
    025/**
    026 * A counting Bloom filter using an int array to track cells for each enabled bit.
    027 *
    028 * <p>
    029 * Any operation that results in negative counts or integer overflow of counts will mark this filter as invalid. This transition is not reversible. The
    030 * operation is completed in full, no exception is raised and the state is set to invalid. This allows the cells for the filter immediately prior to the
    031 * operation that created the invalid state to be recovered. See the documentation in {@link #isValid()} for details.
    032 * </p>
    033 *
    034 * <p>
    035 * All the operations in the filter assume the cells are currently valid, for example {@code cardinality} or {@code contains} operations. Behavior of an invalid
    036 * filter is undefined. It will no longer function identically to a standard Bloom filter that is the merge of all the Bloom filters that have been added to and
    037 * not later subtracted from the counting Bloom filter.
    038 * </p>
    039 *
    040 * <p>
    041 * The maximum supported number of items that can be stored in the filter is limited by the maximum array size combined with the {@link Shape}. For example an
    042 * implementation using a {@link Shape} with a false-positive probability of 1e-6 and {@link Integer#MAX_VALUE} bits can reversibly store approximately 75
    043 * million items using 20 hash functions per item with a memory consumption of approximately 8 GB.
    044 * </p>
    045 *
    046 * @see Shape
    047 * @see CellExtractor
    048 * @since 4.5.0-M1
    049 */
    050public final class ArrayCountingBloomFilter implements CountingBloomFilter {
    051
    052    /**
    053     * The shape of this Bloom filter.
    054     */
    055    private final Shape shape;
    056
    057    /**
    058     * The cell for each bit index in the filter.
    059     */
    060    private final int[] cells;
    061
    062    /**
    063     * The state flag. This is a bitwise {@code OR} of the entire history of all updated
    064     * cells. If negative then a negative cell or integer overflow has occurred on
    065     * one or more cells in the history of the filter and the state is invalid.
    066     *
    067     * <p>Maintenance of this state flag is branch-free for improved performance. It
    068     * eliminates a conditional check for a negative cell during remove/subtract
    069     * operations and a conditional check for integer overflow during merge/add
    070     * operations.</p>
    071     *
    072     * <p>Note: Integer overflow is unlikely in realistic usage scenarios. A cell
    073     * that overflows indicates that the number of items in the filter exceeds the
    074     * maximum possible size (number of bits) of any Bloom filter constrained by
    075     * integer indices. At this point the filter is most likely full (all bits are
    076     * non-zero) and thus useless.</p>
    077     *
    078     * <p>Negative cells are a concern if the filter is used incorrectly by
    079     * removing an item that was never added. It is expected that a user of a
    080     * counting Bloom filter will not perform this action as it is a mistake.
    081     * Enabling an explicit recovery path for negative or overflow cells is a major
    082     * performance burden not deemed necessary for the unlikely scenarios when an
    083     * invalid state is created. Maintenance of the state flag is a concession to
    084     * flag improper use that should not have a major performance impact.</p>
    085     */
    086    private int state;
    087
    088    private ArrayCountingBloomFilter(final ArrayCountingBloomFilter source) {
    089        this.shape = source.shape;
    090        this.state = source.state;
    091        this.cells = source.cells.clone();
    092    }
    093
    094    /**
    095     * Constructs an empty counting Bloom filter with the specified shape.
    096     *
    097     * @param shape the shape of the filter
    098     */
    099    public ArrayCountingBloomFilter(final Shape shape) {
    100        Objects.requireNonNull(shape, "shape");
    101        this.shape = shape;
    102        cells = new int[shape.getNumberOfBits()];
    103    }
    104
    105    @Override
    106    public boolean add(final CellExtractor other) {
    107        Objects.requireNonNull(other, "other");
    108        other.processCells(this::add);
    109        return isValid();
    110    }
    111
    112    /**
    113     * Add to the cell for the bit index.
    114     *
    115     * @param idx the index
    116     * @param addend the amount to add
    117     * @return {@code true} always.
    118     */
    119    private boolean add(final int idx, final int addend) {
    120        try {
    121            final int updated = cells[idx] + addend;
    122            state |= updated;
    123            cells[idx] = updated;
    124            return true;
    125        } catch (final IndexOutOfBoundsException e) {
    126            throw new IllegalArgumentException(
    127                    String.format("Filter only accepts values in the [0,%d) range", getShape().getNumberOfBits()), e);
    128        }
    129    }
    130
    131    @Override
    132    public int[] asIndexArray() {
    133        return IntStream.range(0, cells.length).filter(i -> cells[i] > 0).toArray();
    134    }
    135
    136    @Override
    137    public int cardinality() {
    138        return (int) IntStream.range(0, cells.length).filter(i -> cells[i] > 0).count();
    139    }
    140
    141    @Override
    142    public int characteristics() {
    143        return SPARSE;
    144    }
    145
    146    @Override
    147    public void clear() {
    148        Arrays.fill(cells, 0);
    149    }
    150
    151    @Override
    152    public boolean contains(final BitMapExtractor bitMapExtractor) {
    153        return contains(IndexExtractor.fromBitMapExtractor(bitMapExtractor));
    154    }
    155
    156    @Override
    157    public boolean contains(final IndexExtractor indexExtractor) {
    158        return indexExtractor.processIndices(idx -> cells[idx] != 0);
    159    }
    160
    161    /**
    162     * Creates a new instance of this {@link ArrayCountingBloomFilter} with the same properties as the current one.
    163     *
    164     * @return a copy of this BloomFilter.
    165     */
    166    @Override
    167    public ArrayCountingBloomFilter copy() {
    168        return new ArrayCountingBloomFilter(this);
    169    }
    170
    171    @Override
    172    public int getMaxCell() {
    173        return Integer.MAX_VALUE;
    174    }
    175
    176    @Override
    177    public int getMaxInsert(final CellExtractor cellExtractor) {
    178        final int[] max = { Integer.MAX_VALUE };
    179        cellExtractor.processCells((x, y) -> {
    180            final int count = cells[x] / y;
    181            if (count < max[0]) {
    182                max[0] = count;
    183            }
    184            return max[0] > 0;
    185        });
    186        return max[0];
    187    }
    188
    189    @Override
    190    public Shape getShape() {
    191        return shape;
    192    }
    193
    194    /**
    195     * {@inheritDoc}
    196     *
    197     * <p>
    198     * <em>Implementation note</em>
    199     * </p>
    200     *
    201     * <p>
    202     * The state transition to invalid is permanent.
    203     * </p>
    204     *
    205     * <p>
    206     * This implementation does not correct negative cells to zero or integer overflow cells to {@link Integer#MAX_VALUE}. Thus the operation that generated
    207     * invalid cells can be reversed by using the complement of the original operation with the same Bloom filter. This will restore the cells to the state
    208     * prior to the invalid operation. Cells can then be extracted using {@link #processCells(CellPredicate)}.
    209     * </p>
    210     */
    211    @Override
    212    public boolean isValid() {
    213        return state >= 0;
    214    }
    215
    216    @Override
    217    public boolean processBitMaps(final LongPredicate consumer) {
    218        Objects.requireNonNull(consumer, "consumer");
    219        final int blocksm1 = BitMaps.numberOfBitMaps(cells.length) - 1;
    220        int i = 0;
    221        long value;
    222        // must break final block separate as the number of bits may not fall on the long boundary
    223        for (int j = 0; j < blocksm1; j++) {
    224            value = 0;
    225            for (int k = 0; k < Long.SIZE; k++) {
    226                if (cells[i++] != 0) {
    227                    value |= BitMaps.getLongBit(k);
    228                }
    229            }
    230            if (!consumer.test(value)) {
    231                return false;
    232            }
    233        }
    234        // Final block
    235        value = 0;
    236        for (int k = 0; i < cells.length; k++) {
    237            if (cells[i++] != 0) {
    238                value |= BitMaps.getLongBit(k);
    239            }
    240        }
    241        return consumer.test(value);
    242    }
    243
    244    @Override
    245    public boolean processCells(final CellPredicate consumer) {
    246        Objects.requireNonNull(consumer, "consumer");
    247        for (int i = 0; i < cells.length; i++) {
    248            if (cells[i] != 0 && !consumer.test(i, cells[i])) {
    249                return false;
    250            }
    251        }
    252        return true;
    253    }
    254
    255    @Override
    256    public boolean processIndices(final IntPredicate consumer) {
    257        Objects.requireNonNull(consumer, "consumer");
    258        for (int i = 0; i < cells.length; i++) {
    259            if (cells[i] != 0 && !consumer.test(i)) {
    260                return false;
    261            }
    262        }
    263        return true;
    264    }
    265
    266    @Override
    267    public boolean subtract(final CellExtractor other) {
    268        Objects.requireNonNull(other, "other");
    269        other.processCells(this::subtract);
    270        return isValid();
    271    }
    272
    273    /**
    274     * Subtracts from the cell for the bit index.
    275     *
    276     * @param idx the index
    277     * @param subtrahend the amount to subtract
    278     * @return {@code true} always.
    279     */
    280    private boolean subtract(final int idx, final int subtrahend) {
    281        try {
    282            final int updated = cells[idx] - subtrahend;
    283            state |= updated;
    284            cells[idx] = updated;
    285            return true;
    286        } catch (final IndexOutOfBoundsException e) {
    287            throw new IllegalArgumentException(
    288                    String.format("Filter only accepts values in the [0,%d) range", getShape().getNumberOfBits()), e);
    289        }
    290    }
    291}