| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You 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 org.apache.lucene.util; |
| |
| |
| import java.util.Arrays; |
| import java.util.HashMap; |
| import java.util.Map; |
| |
| /** |
| * A ring buffer that tracks the frequency of the integers that it contains. |
| * This is typically useful to track the hash codes of popular recently-used |
| * items. |
| * |
| * This data-structure requires 22 bytes per entry on average (between 16 and |
| * 28). |
| * |
| * @lucene.internal |
| */ |
| public final class FrequencyTrackingRingBuffer implements Accountable { |
| |
| private static final long BASE_RAM_BYTES_USED = RamUsageEstimator.shallowSizeOfInstance(FrequencyTrackingRingBuffer.class); |
| |
| private final int maxSize; |
| private final int[] buffer; |
| private int position; |
| private final IntBag frequencies; |
| |
| /** Create a new ring buffer that will contain at most <code>maxSize</code> items. |
| * This buffer will initially contain <code>maxSize</code> times the |
| * <code>sentinel</code> value. */ |
| public FrequencyTrackingRingBuffer(int maxSize, int sentinel) { |
| if (maxSize < 2) { |
| throw new IllegalArgumentException("maxSize must be at least 2"); |
| } |
| this.maxSize = maxSize; |
| buffer = new int[maxSize]; |
| position = 0; |
| frequencies = new IntBag(maxSize); |
| |
| Arrays.fill(buffer, sentinel); |
| for (int i = 0; i < maxSize; ++i) { |
| frequencies.add(sentinel); |
| } |
| assert frequencies.frequency(sentinel) == maxSize; |
| } |
| |
| @Override |
| public long ramBytesUsed() { |
| return BASE_RAM_BYTES_USED |
| + frequencies.ramBytesUsed() |
| + RamUsageEstimator.sizeOf(buffer); |
| } |
| |
| /** |
| * Add a new item to this ring buffer, potentially removing the oldest |
| * entry from this buffer if it is already full. |
| */ |
| public void add(int i) { |
| // remove the previous value |
| final int removed = buffer[position]; |
| final boolean removedFromBag = frequencies.remove(removed); |
| assert removedFromBag; |
| // add the new value |
| buffer[position] = i; |
| frequencies.add(i); |
| // increment the position |
| position += 1; |
| if (position == maxSize) { |
| position = 0; |
| } |
| } |
| |
| /** |
| * Returns the frequency of the provided key in the ring buffer. |
| */ |
| public int frequency(int key) { |
| return frequencies.frequency(key); |
| } |
| |
| // pkg-private for testing |
| Map<Integer, Integer> asFrequencyMap() { |
| return frequencies.asMap(); |
| } |
| |
| /** |
| * A bag of integers. |
| * Since in the context of the ring buffer the maximum size is known up-front |
| * there is no need to worry about resizing the underlying storage. |
| */ |
| private static class IntBag implements Accountable { |
| |
| private static final long BASE_RAM_BYTES_USED = RamUsageEstimator.shallowSizeOfInstance(IntBag.class); |
| |
| private final int[] keys; |
| private final int[] freqs; |
| private final int mask; |
| |
| IntBag(int maxSize) { |
| // load factor of 2/3 |
| int capacity = Math.max(2, maxSize * 3 / 2); |
| // round up to the next power of two |
| capacity = Integer.highestOneBit(capacity - 1) << 1; |
| assert capacity > maxSize; |
| keys = new int[capacity]; |
| freqs = new int[capacity]; |
| mask = capacity - 1; |
| } |
| |
| @Override |
| public long ramBytesUsed() { |
| return BASE_RAM_BYTES_USED |
| + RamUsageEstimator.sizeOf(keys) |
| + RamUsageEstimator.sizeOf(freqs); |
| } |
| |
| /** Return the frequency of the give key in the bag. */ |
| int frequency(int key) { |
| for (int slot = key & mask; ; slot = (slot + 1) & mask) { |
| if (keys[slot] == key) { |
| return freqs[slot]; |
| } else if (freqs[slot] == 0) { |
| return 0; |
| } |
| } |
| } |
| |
| /** Increment the frequency of the given key by 1 and return its new frequency. */ |
| int add(int key) { |
| for (int slot = key & mask; ; slot = (slot + 1) & mask) { |
| if (freqs[slot] == 0) { |
| keys[slot] = key; |
| return freqs[slot] = 1; |
| } else if (keys[slot] == key) { |
| return ++freqs[slot]; |
| } |
| } |
| } |
| |
| /** Decrement the frequency of the given key by one, or do nothing if the |
| * key is not present in the bag. Returns true iff the key was contained |
| * in the bag. */ |
| boolean remove(int key) { |
| for (int slot = key & mask; ; slot = (slot + 1) & mask) { |
| if (freqs[slot] == 0) { |
| // no such key in the bag |
| return false; |
| } else if (keys[slot] == key) { |
| final int newFreq = --freqs[slot]; |
| if (newFreq == 0) { // removed |
| relocateAdjacentKeys(slot); |
| } |
| return true; |
| } |
| } |
| } |
| |
| private void relocateAdjacentKeys(int freeSlot) { |
| for (int slot = (freeSlot + 1) & mask; ; slot = (slot + 1) & mask) { |
| final int freq = freqs[slot]; |
| if (freq == 0) { |
| // end of the collision chain, we're done |
| break; |
| } |
| final int key = keys[slot]; |
| // the slot where <code>key</code> should be if there were no collisions |
| final int expectedSlot = key & mask; |
| // if the free slot is between the expected slot and the slot where the |
| // key is, then we can relocate there |
| if (between(expectedSlot, slot, freeSlot)) { |
| keys[freeSlot] = key; |
| freqs[freeSlot] = freq; |
| // slot is the new free slot |
| freqs[slot] = 0; |
| freeSlot = slot; |
| } |
| } |
| } |
| |
| /** Given a chain of occupied slots between <code>chainStart</code> |
| * and <code>chainEnd</code>, return whether <code>slot</code> is |
| * between the start and end of the chain. */ |
| private static boolean between(int chainStart, int chainEnd, int slot) { |
| if (chainStart <= chainEnd) { |
| return chainStart <= slot && slot <= chainEnd; |
| } else { |
| // the chain is across the end of the array |
| return slot >= chainStart || slot <= chainEnd; |
| } |
| } |
| |
| Map<Integer, Integer> asMap() { |
| Map<Integer, Integer> map = new HashMap<>(); |
| for (int i = 0; i < keys.length; ++i) { |
| if (freqs[i] > 0) { |
| map.put(keys[i], freqs[i]); |
| } |
| } |
| return map; |
| } |
| |
| } |
| |
| } |