package org.apache.lucene.search;
/**
* 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.
*/
import java.util.Comparator;
import java.util.Date;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.TreeSet;
import org.apache.lucene.util.ThreadInterruptedException;
/**
* Filter caching singleton. It can be used
* to save filters locally for reuse.
* This class makes it possible to cache Filters even when using RMI, as it
* keeps the cache on the searcher side of the RMI connection.
*
* Also could be used as a persistent storage for any filter as long as the
* filter provides a proper hashCode(), as that is used as the key in the cache.
*
* The cache is periodically cleaned up from a separate thread to ensure the
* cache doesn't exceed the maximum size.
*/
public class FilterManager {
protected static FilterManager manager;
/** The default maximum number of Filters in the cache */
protected static final int DEFAULT_CACHE_CLEAN_SIZE = 100;
/** The default frequency of cache cleanup */
protected static final long DEFAULT_CACHE_SLEEP_TIME = 1000 * 60 * 10;
/** The cache itself */
protected Map<Integer,FilterItem> cache;
/** Maximum allowed cache size */
protected int cacheCleanSize;
/** Cache cleaning frequency */
protected long cleanSleepTime;
/** Cache cleaner that runs in a separate thread */
protected FilterCleaner filterCleaner;
public synchronized static FilterManager getInstance() {
if (manager == null) {
manager = new FilterManager();
}
return manager;
}
/**
* Sets up the FilterManager singleton.
*/
protected FilterManager() {
cache = new HashMap<Integer,FilterItem>();
cacheCleanSize = DEFAULT_CACHE_CLEAN_SIZE; // Let the cache get to 100 items
cleanSleepTime = DEFAULT_CACHE_SLEEP_TIME; // 10 minutes between cleanings
filterCleaner = new FilterCleaner();
Thread fcThread = new Thread(filterCleaner);
// set to be a Daemon so it doesn't have to be stopped
fcThread.setDaemon(true);
fcThread.start();
}
/**
* Sets the max size that cache should reach before it is cleaned up
* @param cacheCleanSize maximum allowed cache size
*/
public void setCacheSize(int cacheCleanSize) {
this.cacheCleanSize = cacheCleanSize;
}
/**
* Sets the cache cleaning frequency in milliseconds.
* @param cleanSleepTime cleaning frequency in milliseconds
*/
public void setCleanThreadSleepTime(long cleanSleepTime) {
this.cleanSleepTime = cleanSleepTime;
}
/**
* Returns the cached version of the filter. Allows the caller to pass up
* a small filter but this will keep a persistent version around and allow
* the caching filter to do its job.
*
* @param filter The input filter
* @return The cached version of the filter
*/
public Filter getFilter(Filter filter) {
synchronized(cache) {
FilterItem fi = null;
fi = cache.get(Integer.valueOf(filter.hashCode()));
if (fi != null) {
fi.timestamp = new Date().getTime();
return fi.filter;
}
cache.put(Integer.valueOf(filter.hashCode()), new FilterItem(filter));
return filter;
}
}
/**
* Holds the filter and the last time the filter was used, to make LRU-based
* cache cleaning possible.
* TODO: Clean this up when we switch to Java 1.5
*/
protected class FilterItem {
public Filter filter;
public long timestamp;
public FilterItem (Filter filter) {
this.filter = filter;
this.timestamp = new Date().getTime();
}
}
/**
* Keeps the cache from getting too big.
* If we were using Java 1.5, we could use LinkedHashMap and we would not need this thread
* to clean out the cache.
*
* The SortedSet sortedFilterItems is used only to sort the items from the cache,
* so when it's time to clean up we have the TreeSet sort the FilterItems by
* timestamp.
*
* Removes 1.5 * the numbers of items to make the cache smaller.
* For example:
* 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.
* This way we clean the cache a bit more, and avoid having the cache cleaner having to do it frequently.
*/
protected class FilterCleaner implements Runnable {
private boolean running = true;
private TreeSet<Map.Entry<Integer,FilterItem>> sortedFilterItems;
public FilterCleaner() {
sortedFilterItems = new TreeSet<Map.Entry<Integer,FilterItem>>(new Comparator<Map.Entry<Integer,FilterItem>>() {
public int compare(Map.Entry<Integer,FilterItem> a, Map.Entry<Integer,FilterItem> b) {
FilterItem fia = a.getValue();
FilterItem fib = b.getValue();
if ( fia.timestamp == fib.timestamp ) {
return 0;
}
// smaller timestamp first
if ( fia.timestamp < fib.timestamp ) {
return -1;
}
// larger timestamp last
return 1;
}
});
}
public void run () {
while (running) {
// sort items from oldest to newest
// we delete the oldest filters
if (cache.size() > cacheCleanSize) {
// empty the temporary set
sortedFilterItems.clear();
synchronized (cache) {
sortedFilterItems.addAll(cache.entrySet());
Iterator<Map.Entry<Integer,FilterItem>> it = sortedFilterItems.iterator();
int numToDelete = (int) ((cache.size() - cacheCleanSize) * 1.5);
int counter = 0;
// loop over the set and delete all of the cache entries not used in a while
while (it.hasNext() && counter++ < numToDelete) {
Map.Entry<Integer,FilterItem> entry = it.next();
cache.remove(entry.getKey());
}
}
// empty the set so we don't tie up the memory
sortedFilterItems.clear();
}
// take a nap
try {
Thread.sleep(cleanSleepTime);
} catch (InterruptedException ie) {
throw new ThreadInterruptedException(ie);
}
}
}
}
}