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/*
* 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.
*/
using System;
using System.Collections.Generic;
using System.Linq;
using Lucene.Net.Support;
namespace Lucene.Net.Search
{
/// <summary> Filter caching singleton. It can be used
/// to save filters locally for reuse.
/// This class makes it possble to cache Filters even when using RMI, as it
/// keeps the cache on the seaercher 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.
/// </summary>
public class FilterManager
{
protected internal static FilterManager manager;
/// <summary>The default maximum number of Filters in the cache </summary>
protected internal const int DEFAULT_CACHE_CLEAN_SIZE = 100;
/// <summary>The default frequency of cache clenup </summary>
protected internal const long DEFAULT_CACHE_SLEEP_TIME = 1000 * 60 * 10;
/// <summary>The cache itself </summary>
protected internal IDictionary<int, FilterItem> cache;
/// <summary>Maximum allowed cache size </summary>
protected internal int cacheCleanSize;
/// <summary>Cache cleaning frequency </summary>
protected internal long cleanSleepTime;
/// <summary>Cache cleaner that runs in a separate thread </summary>
protected internal FilterCleaner internalFilterCleaner;
private static readonly object _staticSyncObj = new object();
public static FilterManager Instance
{
get
{
lock (_staticSyncObj)
{
return manager ?? (manager = new FilterManager());
}
}
}
/// <summary> Sets up the FilterManager singleton.</summary>
protected internal FilterManager()
{
cache = new HashMap<int, FilterItem>();
cacheCleanSize = DEFAULT_CACHE_CLEAN_SIZE; // Let the cache get to 100 items
cleanSleepTime = DEFAULT_CACHE_SLEEP_TIME; // 10 minutes between cleanings
internalFilterCleaner = new FilterCleaner(this);
ThreadClass fcThread = new ThreadClass(new System.Threading.ThreadStart(internalFilterCleaner.Run));
// setto be a Daemon so it doesn't have to be stopped
fcThread.IsBackground = true;
fcThread.Start();
}
/// <summary> Sets the max size that cache should reach before it is cleaned up</summary>
/// <param name="value"> maximum allowed cache size </param>
public virtual void SetCacheSize(int value)
{
this.cacheCleanSize = value;
}
/// <summary> Sets the cache cleaning frequency in milliseconds.</summary>
/// <param name="value"> cleaning frequency in millioseconds </param>
public virtual void SetCleanThreadSleepTime(long value)
{
this.cleanSleepTime = value;
}
/// <summary> 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.
///
/// </summary>
/// <param name="filter">The input filter
/// </param>
/// <returns> The cached version of the filter
/// </returns>
public virtual Filter GetFilter(Filter filter)
{
lock (cache)
{
FilterItem fi = null;
fi = cache[filter.GetHashCode()];
if (fi != null)
{
fi.timestamp = System.DateTime.UtcNow.Ticks;
return fi.filter;
}
cache[filter.GetHashCode()] = new FilterItem(filter);
return filter;
}
}
/// <summary> 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
/// </summary>
protected internal class FilterItem
{
public Filter filter;
public long timestamp;
public FilterItem(Filter filter)
{
this.filter = filter;
this.timestamp = System.DateTime.UtcNow.Ticks;
}
}
/// <summary> 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.
/// </summary>
protected internal class FilterCleaner : IThreadRunnable
{
private class FilterItemComparer : IComparer<KeyValuePair<int, FilterItem>>
{
#region IComparer<FilterItem> Members
public int Compare(KeyValuePair<int, FilterItem> x, KeyValuePair<int, FilterItem> y)
{
return x.Value.timestamp.CompareTo(y.Value.timestamp);
}
#endregion
}
private bool running = true;
private FilterManager manager;
private ISet<KeyValuePair<int, FilterItem>> sortedFilterItems;
public FilterCleaner(FilterManager enclosingInstance)
{
this.manager = enclosingInstance;
sortedFilterItems = new SortedSet<KeyValuePair<int, FilterItem>>(new FilterItemComparer());
}
public virtual void Run()
{
while (running)
{
// sort items from oldest to newest
// we delete the oldest filters
if (this.manager.cache.Count > this.manager.cacheCleanSize)
{
// empty the temporary set
sortedFilterItems.Clear();
lock (this.manager.cache)
{
sortedFilterItems.UnionWith(this.manager.cache);
int numToDelete = (int)((this.manager.cache.Count - this.manager.cacheCleanSize) * 1.5);
//delete all of the cache entries not used in a while
sortedFilterItems.ExceptWith(sortedFilterItems.Take(numToDelete).ToArray());
}
// empty the set so we don't tie up the memory
sortedFilterItems.Clear();
}
// take a nap
System.Threading.Thread.Sleep(new System.TimeSpan((System.Int64)10000 * this.manager.cleanSleepTime));
}
}
}
}
}
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