| /* |
| * 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.jackrabbit.oak.segment.file; |
| |
| import static org.apache.jackrabbit.guava.common.base.Preconditions.checkArgument; |
| import static org.apache.jackrabbit.guava.common.base.Preconditions.checkNotNull; |
| import static java.lang.Integer.bitCount; |
| import static java.lang.Integer.numberOfTrailingZeros; |
| import static java.lang.Long.numberOfLeadingZeros; |
| import static java.lang.Math.max; |
| import static java.util.Arrays.fill; |
| |
| import org.apache.jackrabbit.guava.common.cache.CacheStats; |
| import org.apache.jackrabbit.guava.common.cache.Weigher; |
| import org.apache.jackrabbit.oak.segment.CacheWeights; |
| import org.jetbrains.annotations.NotNull; |
| import org.jetbrains.annotations.Nullable; |
| |
| import org.apache.jackrabbit.guava.common.base.Predicate; |
| import org.apache.jackrabbit.guava.common.base.Supplier; |
| |
| /** |
| * {@code PriorityCache} implements a partial mapping from keys of type {@code K} to values |
| * of type {@code V}. Mappings are associates with a cost, which states how expensive it is |
| * to recreate that mapping. This cache uses the cost such that mappings with a higher cost |
| * have a lower chance of being evicted than mappings with a lower cost. When an item from |
| * this cache is successfully looked up its cost is incremented by one, unless it has reached |
| * its maximum cost of {@link Byte#MAX_VALUE} already. |
| * <p> |
| * Additionally this cache tracks a generation for mappings. Mappings of later generations |
| * always take precedence over mappings of earlier generations. That is, putting a mapping of |
| * a later generation into the cache can cause any mapping of an earlier generation to be evicted |
| * regardless of its cost. |
| * <p> |
| * This cache uses rehashing to resolve clashes. The number of rehashes is configurable. When |
| * a clash cannot be resolved by rehashing the given number of times the put operation fails. |
| * <p> |
| * This cache is thread safe. |
| * @param <K> type of the keys |
| * @param <V> type of the values |
| */ |
| public class PriorityCache<K, V> { |
| private final int rehash; |
| private final Entry<?,?>[] entries; |
| private final int[] costs = new int[256]; |
| private final int[] evictions = new int[256]; |
| |
| private long hitCount; |
| private long missCount; |
| private long loadCount; |
| private long loadExceptionCount; |
| private long evictionCount; |
| private long size; |
| |
| @NotNull |
| private final Weigher<K, V> weigher; |
| private long weight = 0; |
| |
| /** |
| * Static factory for creating new {@code PriorityCache} instances. |
| * @param size size of the cache. Must be a power of 2. |
| * @return a new {@code PriorityCache} instance of the given {@code size}. |
| */ |
| public static <K, V> Supplier<PriorityCache<K, V>> factory(final int size, @NotNull final Weigher<K, V> weigher) { |
| checkArgument(bitCount(size) == 1); |
| checkNotNull(weigher); |
| return new Supplier<PriorityCache<K, V>>() { |
| @Override |
| public PriorityCache<K, V> get() { |
| return new PriorityCache<>(size, weigher); |
| } |
| }; |
| } |
| |
| /** |
| * Static factory for creating new {@code PriorityCache} instances. |
| * @param size size of the cache. Must be a power of 2. |
| * @return a new {@code PriorityCache} instance of the given {@code size}. |
| */ |
| public static <K, V> Supplier<PriorityCache<K, V>> factory(final int size) { |
| checkArgument(bitCount(size) == 1); |
| return new Supplier<PriorityCache<K, V>>() { |
| @Override |
| public PriorityCache<K, V> get() { |
| return new PriorityCache<>(size); |
| } |
| }; |
| } |
| |
| private static class Entry<K, V> { |
| static final Entry<Void, Void> NULL = new Entry<>(null, null, -1, Byte.MIN_VALUE); |
| |
| final K key; |
| final V value; |
| final int generation; |
| byte cost; |
| |
| public Entry(K key, V value, int generation, byte cost) { |
| this.key = key; |
| this.value = value; |
| this.generation = generation; |
| this.cost = cost; |
| } |
| |
| @Override |
| public String toString() { |
| return this == NULL |
| ? "NULL" |
| : "Entry{" + key + "->" + value + " @" + generation + ", $" + cost + "}"; |
| } |
| } |
| |
| /** |
| * Round {@code size} up to the next power of two or 1 for negative values. |
| * @param size |
| * @return the next power of two starting from {@code size}. |
| */ |
| public static long nextPowerOfTwo(int size) { |
| return 1L << (64L - numberOfLeadingZeros((long)max(1, size) - 1L)); |
| } |
| |
| /** |
| * Create a new instance of the given {@code size}. {@code rehash} specifies the number |
| * of rehashes to resolve a clash. |
| * @param size Size of the cache. Must be a power of {@code 2}. |
| * @param rehash Number of rehashes. Must be greater or equal to {@code 0} and |
| * smaller than {@code 32 - numberOfTrailingZeros(size)}. |
| */ |
| PriorityCache(int size, int rehash) { |
| this(size, rehash, CacheWeights.<K, V> noopWeigher()); |
| } |
| |
| /** |
| * Create a new instance of the given {@code size}. {@code rehash} specifies the number |
| * of rehashes to resolve a clash. |
| * @param size Size of the cache. Must be a power of {@code 2}. |
| * @param rehash Number of rehashes. Must be greater or equal to {@code 0} and |
| * smaller than {@code 32 - numberOfTrailingZeros(size)}. |
| * @param weigher Needed to provide an estimation of the cache weight in memory |
| */ |
| public PriorityCache(int size, int rehash, @NotNull Weigher<K, V> weigher) { |
| checkArgument(bitCount(size) == 1); |
| checkArgument(rehash >= 0); |
| checkArgument(rehash < 32 - numberOfTrailingZeros(size)); |
| this.rehash = rehash; |
| entries = new Entry<?,?>[size]; |
| fill(entries, Entry.NULL); |
| this.weigher = checkNotNull(weigher); |
| } |
| |
| /** |
| * Create a new instance of the given {@code size}. The number of rehashes is |
| * the maximum number allowed by the given {@code size}. ({@code 31 - numberOfTrailingZeros(size)}. |
| * @param size Size of the cache. Must be a power of {@code 2}. |
| */ |
| public PriorityCache(int size, @NotNull Weigher<K, V> weigher) { |
| this(size, 31 - numberOfTrailingZeros(size), weigher); |
| } |
| |
| public PriorityCache(int size) { |
| this(size, 31 - numberOfTrailingZeros(size)); |
| } |
| |
| private int project(int hashCode, int iteration) { |
| return (hashCode >> iteration) & (entries.length - 1); |
| } |
| |
| /** |
| * @return the number of mappings in this cache. |
| */ |
| public long size() { |
| return size; |
| } |
| |
| /** |
| * Add a mapping to the cache. |
| * @param key the key of the mapping |
| * @param value the value of the mapping |
| * @param generation the generation of the mapping |
| * @param initialCost the initial cost associated with this mapping |
| * @return {@code true} if the mapping has been added, {@code false} otherwise. |
| */ |
| public synchronized boolean put(@NotNull K key, @NotNull V value, int generation, byte initialCost) { |
| int hashCode = key.hashCode(); |
| byte cheapest = initialCost; |
| int index = -1; |
| boolean eviction = false; |
| for (int k = 0; k <= rehash; k++) { |
| int i = project(hashCode, k); |
| Entry<?, ?> entry = entries[i]; |
| if (entry == Entry.NULL) { |
| // Empty slot -> use this index |
| index = i; |
| eviction = false; |
| break; |
| } else if (entry.generation <= generation && key.equals(entry.key)) { |
| // Key exists and generation is greater or equal -> use this index and boost the cost |
| index = i; |
| initialCost = entry.cost; |
| if (initialCost < Byte.MAX_VALUE) { |
| initialCost++; |
| } |
| eviction = false; |
| break; |
| } else if (entry.generation < generation) { |
| // Old generation -> use this index |
| index = i; |
| eviction = false; |
| break; |
| } else if (entry.cost < cheapest) { |
| // Candidate slot, keep on searching for even cheaper slots |
| cheapest = entry.cost; |
| index = i; |
| eviction = true; |
| } |
| } |
| |
| if (index >= 0) { |
| Entry<?, ?> old = entries[index]; |
| Entry<?, ?> newE = new Entry<>(key, value, generation, initialCost); |
| entries[index] = newE; |
| loadCount++; |
| costs[initialCost - Byte.MIN_VALUE]++; |
| if (old != Entry.NULL) { |
| costs[old.cost - Byte.MIN_VALUE]--; |
| if (eviction) { |
| evictions[old.cost - Byte.MIN_VALUE]++; |
| evictionCount++; |
| } |
| weight -= weighEntry(old); |
| } else { |
| size++; |
| } |
| weight += weighEntry(newE); |
| return true; |
| } else { |
| loadExceptionCount++; |
| return false; |
| } |
| } |
| |
| /** |
| * Look up a mapping from this cache by its {@code key} and {@code generation}. |
| * @param key key of the mapping to look up |
| * @param generation generation of the mapping to look up |
| * @return the mapping for {@code key} and {@code generation} or {@code null} if this |
| * cache does not contain such a mapping. |
| */ |
| @SuppressWarnings("unchecked") |
| @Nullable |
| public synchronized V get(@NotNull K key, int generation) { |
| int hashCode = key.hashCode(); |
| for (int k = 0; k <= rehash; k++) { |
| int i = project(hashCode, k); |
| Entry<?, ?> entry = entries[i]; |
| if (generation == entry.generation && key.equals(entry.key)) { |
| if (entry.cost < Byte.MAX_VALUE) { |
| costs[entry.cost - Byte.MIN_VALUE]--; |
| entry.cost++; |
| costs[entry.cost - Byte.MIN_VALUE]++; |
| } |
| hitCount++; |
| return (V) entry.value; |
| } |
| } |
| missCount++; |
| return null; |
| } |
| |
| /** |
| * Purge all keys from this cache whose entry's generation matches the |
| * passed {@code purge} predicate. |
| * @param purge |
| */ |
| public synchronized void purgeGenerations(@NotNull Predicate<Integer> purge) { |
| for (int i = 0; i < entries.length; i++) { |
| Entry<?, ?> entry = entries[i]; |
| if (entry != Entry.NULL && purge.apply(entry.generation)) { |
| entries[i] = Entry.NULL; |
| size--; |
| weight -= weighEntry(entry); |
| } |
| } |
| } |
| |
| @SuppressWarnings("unchecked") |
| private int weighEntry(Entry<?, ?> entry) { |
| return weigher.weigh((K) entry.key, (V) entry.value); |
| } |
| |
| @Override |
| public synchronized String toString() { |
| return "PriorityCache" + |
| "{ costs=" + toString(costs) + |
| ", evictions=" + toString(evictions) + " }"; |
| } |
| |
| private static String toString(int[] ints) { |
| StringBuilder b = new StringBuilder("["); |
| String sep = ""; |
| for (int i = 0; i < ints.length; i++) { |
| if (ints[i] > 0) { |
| b.append(sep).append(i).append("->").append(ints[i]); |
| sep = ","; |
| } |
| } |
| return b.append(']').toString(); |
| } |
| |
| /** |
| * @return access statistics for this cache |
| */ |
| @NotNull |
| public CacheStats getStats() { |
| return new CacheStats(hitCount, missCount, loadCount, loadExceptionCount, 0, evictionCount); |
| } |
| |
| public long estimateCurrentWeight() { |
| return weight; |
| } |
| |
| } |