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package org.apache.lucene.search;
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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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import java.util.Comparator;
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import java.util.Date;
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import java.util.HashMap;
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import java.util.Iterator;
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import java.util.TreeSet;
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import org.apache.lucene.util.ThreadInterruptedException;
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* Filter caching singleton. It can be used to save filters locally for reuse.
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* This class makes it possible to cache Filters even when using RMI, as it
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* keeps the cache on the searcher side of the RMI connection.
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* Also could be used as a persistent storage for any filter as long as the
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* filter provides a proper hashCode(), as that is used as the key in the cache.
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* The cache is periodically cleaned up from a separate thread to ensure the
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* cache doesn't exceed the maximum size.
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* @deprecated used by remote package which is deprecated as well. You should
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* use {@link CachingWrapperFilter} if you wish to cache
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public class FilterManager {
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protected static FilterManager manager;
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/** The default maximum number of Filters in the cache */
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protected static final int DEFAULT_CACHE_CLEAN_SIZE = 100;
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/** The default frequency of cache cleanup */
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protected static final long DEFAULT_CACHE_SLEEP_TIME = 1000 * 60 * 10;
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/** The cache itself */
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protected Map<Integer,FilterItem> cache;
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/** Maximum allowed cache size */
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protected int cacheCleanSize;
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/** Cache cleaning frequency */
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protected long cleanSleepTime;
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/** Cache cleaner that runs in a separate thread */
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protected FilterCleaner filterCleaner;
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public synchronized static FilterManager getInstance() {
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if (manager == null) {
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manager = new FilterManager();
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* Sets up the FilterManager singleton.
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protected FilterManager() {
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cache = new HashMap<Integer,FilterItem>();
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cacheCleanSize = DEFAULT_CACHE_CLEAN_SIZE; // Let the cache get to 100 items
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cleanSleepTime = DEFAULT_CACHE_SLEEP_TIME; // 10 minutes between cleanings
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filterCleaner = new FilterCleaner();
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Thread fcThread = new Thread(filterCleaner);
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// set to be a Daemon so it doesn't have to be stopped
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fcThread.setDaemon(true);
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* Sets the max size that cache should reach before it is cleaned up
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* @param cacheCleanSize maximum allowed cache size
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public void setCacheSize(int cacheCleanSize) {
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this.cacheCleanSize = cacheCleanSize;
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* Sets the cache cleaning frequency in milliseconds.
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* @param cleanSleepTime cleaning frequency in milliseconds
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public void setCleanThreadSleepTime(long cleanSleepTime) {
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this.cleanSleepTime = cleanSleepTime;
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* Returns the cached version of the filter. Allows the caller to pass up
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* a small filter but this will keep a persistent version around and allow
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* the caching filter to do its job.
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* @param filter The input filter
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* @return The cached version of the filter
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public Filter getFilter(Filter filter) {
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synchronized(cache) {
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FilterItem fi = null;
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fi = cache.get(Integer.valueOf(filter.hashCode()));
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fi.timestamp = new Date().getTime();
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cache.put(Integer.valueOf(filter.hashCode()), new FilterItem(filter));
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* Holds the filter and the last time the filter was used, to make LRU-based
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* cache cleaning possible.
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* TODO: Clean this up when we switch to Java 1.5
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protected class FilterItem {
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public Filter filter;
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public long timestamp;
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public FilterItem (Filter filter) {
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this.filter = filter;
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this.timestamp = new Date().getTime();
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* Keeps the cache from getting too big.
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* If we were using Java 1.5, we could use LinkedHashMap and we would not need this thread
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* to clean out the cache.
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* The SortedSet sortedFilterItems is used only to sort the items from the cache,
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* so when it's time to clean up we have the TreeSet sort the FilterItems by
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* Removes 1.5 * the numbers of items to make the cache smaller.
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* If cache clean size is 10, and the cache is at 15, we would remove (15 - 10) * 1.5 = 7.5 round up to 8.
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* This way we clean the cache a bit more, and avoid having the cache cleaner having to do it frequently.
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protected class FilterCleaner implements Runnable {
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private boolean running = true;
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private TreeSet<Map.Entry<Integer,FilterItem>> sortedFilterItems;
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public FilterCleaner() {
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sortedFilterItems = new TreeSet<Map.Entry<Integer,FilterItem>>(new Comparator<Map.Entry<Integer,FilterItem>>() {
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public int compare(Map.Entry<Integer,FilterItem> a, Map.Entry<Integer,FilterItem> b) {
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FilterItem fia = a.getValue();
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FilterItem fib = b.getValue();
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if ( fia.timestamp == fib.timestamp ) {
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// smaller timestamp first
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if ( fia.timestamp < fib.timestamp ) {
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// larger timestamp last
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// sort items from oldest to newest
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// we delete the oldest filters
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if (cache.size() > cacheCleanSize) {
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// empty the temporary set
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sortedFilterItems.clear();
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synchronized (cache) {
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sortedFilterItems.addAll(cache.entrySet());
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Iterator<Map.Entry<Integer,FilterItem>> it = sortedFilterItems.iterator();
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int numToDelete = (int) ((cache.size() - cacheCleanSize) * 1.5);
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// loop over the set and delete all of the cache entries not used in a while
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while (it.hasNext() && counter++ < numToDelete) {
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Map.Entry<Integer,FilterItem> entry = it.next();
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cache.remove(entry.getKey());
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// empty the set so we don't tie up the memory
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sortedFilterItems.clear();
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Thread.sleep(cleanSleepTime);
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} catch (InterruptedException ie) {
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throw new ThreadInterruptedException(ie);