CloseableThreadLocal

CloseableThreadLocal.cs

/* 
 * 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.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Threading;

namespace Lucene.Net.Util
{
	
	/// <summary>Java's builtin ThreadLocal has a serious flaw:
	/// it can take an arbitrarily long amount of time to
	/// dereference the things you had stored in it, even once the
	/// ThreadLocal instance itself is no longer referenced.
	/// This is because there is single, master map stored for
	/// each thread, which all ThreadLocals share, and that
	/// master map only periodically purges "stale" entries.
	/// 
	/// While not technically a memory leak, because eventually
	/// the memory will be reclaimed, it can take a long time
	/// and you can easily hit OutOfMemoryError because from the
	/// GC's standpoint the stale entries are not reclaimaible.
	/// 
	/// This class works around that, by only enrolling
	/// WeakReference values into the ThreadLocal, and
	/// separately holding a hard reference to each stored
	/// value.  When you call {@link #close}, these hard
	/// references are cleared and then GC is freely able to
	/// reclaim space by objects stored in it. 
	/// </summary>
	
	///<remarks>
	/// .NET doesn't have this problem, this was adapted to use the .NET version
	/// </remarks>
	public class CloseableThreadLocal
	{
		ThreadLocal<object> self ;
		private string guid;

		private static readonly ConcurrentDictionary<string, Dump> tracker = new ConcurrentDictionary<string, Dump>();

		public CloseableThreadLocal()
		{
			guid = Guid.NewGuid().ToString();
			tracker[guid] = new Dump
			{
				StackTrace = new StackTrace(true),
				TimeStamp = DateTime.Now
			};
				
			self = new ThreadLocal<object>(InitialValue);
		}

		public static void DumpTracked()
		{
			var now = DateTime.Now;
			using (var stream = new StreamWriter("dump_history.log", true))
			{
				stream.WriteLine("{0}, {1}", now.ToString("yyyy-MM-ddTHH:mm:ssZ"), tracker.Count);
			}

			using (var stream = new StreamWriter("dump.log"))
			foreach (var dump in tracker.Where(x => (now - x.Value.TimeStamp) > TimeSpan.FromMinutes(5)).OrderBy(x => x.Value.TimeStamp))
			{
				stream.WriteLine("Age={0}, Creation-Time={1}, Id={2}", now - dump.Value.TimeStamp,  dump.Value.TimeStamp, dump.Key);
				stream.WriteLine(dump.Value.StackTrace);
				stream.WriteLine();
				stream.WriteLine();
			}
		}

		public  virtual System.Object InitialValue()
		{
			return null;
		}
		public virtual System.Object Get()
		{
			return self.Value;
		}
		
		public virtual void  Set(System.Object object_Renamed)
		{
			self.Value = object_Renamed;
		}
		
		public virtual void  Close()
		{
			Dump dump;
			tracker.TryRemove(guid, out dump);
			self.Value = null;
			self.Dispose();
		}

		public class Dump
		{
			public StackTrace StackTrace { get; set; }
			public DateTime TimeStamp { get; set; }
		}
	}
}