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package org.apache.lucene.facet.taxonomy.writercache.lru;
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import java.util.HashMap;
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import java.util.Iterator;
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import java.util.LinkedHashMap;
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import org.apache.lucene.facet.taxonomy.CategoryPath;
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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* An an LRU cache of mapping from name to int.
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* Used to cache Ordinals of category paths.
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* @lucene.experimental
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// Note: Nothing in this class is synchronized. The caller is assumed to be
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// synchronized so that no two methods of this class are called concurrently.
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class NameIntCacheLRU {
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private HashMap<Object, Integer> cache;
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long nMisses = 0; // for debug
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long nHits = 0; // for debug
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private int maxCacheSize;
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NameIntCacheLRU(int maxCacheSize) {
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this.maxCacheSize = maxCacheSize;
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createCache(maxCacheSize);
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public int getMaxSize() {
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public int getSize() {
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private void createCache (int maxSize) {
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if (maxSize<Integer.MAX_VALUE) {
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cache = new LinkedHashMap<Object, Integer>(1000,(float)0.7,true); //for LRU
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cache = new HashMap<Object, Integer>(1000,(float)0.7); //no need for LRU
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Integer get (CategoryPath name) {
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Integer res = cache.get(key(name));
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* Subclasses can override this to provide caching by e.g. hash of the string.
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Object key(CategoryPath name) {
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// Note that a copy constructor (cloning) here is necessary, because a
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// CategoryPath object is mutable, so we cannot save a reference to an
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// existing CategoryPath. Subclasses which override this method can
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// avoid this cloning by, e.g., hashing the name.
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return new CategoryPath(name);
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Object key(CategoryPath name, int prefixLen) {
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// Note that a copy constructor (cloning) here is necessary, because a
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// CategoryPath object is mutable, so we cannot save a reference to an
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// existing CategoryPath. Subclasses which override this method can
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// avoid this cloning by, e.g., hashing the name.
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return new CategoryPath(name, prefixLen);
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* Add a new value to cache.
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* Return true if cache became full and some room need to be made.
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boolean put (CategoryPath name, Integer val) {
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cache.put(key(name), val);
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boolean put (CategoryPath name, int prefixLen, Integer val) {
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cache.put(key(name, prefixLen), val);
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return isCacheFull();
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private boolean isCacheFull() {
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return (cache.size()>maxCacheSize);
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return "#miss="+nMisses+" #hit="+nHits;
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* If cache is full remove least recently used entries from cache.
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* Return true if anything was removed, false otherwise.
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* See comment in {@link DirectoryTaxonomyWriter#addToCache(String, Integer)}
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* for an explanation why we clean 2/3rds of the cache, and not just one
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boolean makeRoomLRU() {
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if (!isCacheFull()) {
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int n = cache.size() - (2*maxCacheSize)/3;
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Iterator<Object> it = cache.keySet().iterator();
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while (i<n && it.hasNext()) {