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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 System.Threading;
using Lucene.Net.Support;
#if NET35
using Lucene.Net.Support.Compatibility;
#endif
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 <see cref="Close" />, these hard
/// references are cleared and then GC is freely able to
/// reclaim space by objects stored in it.
/// </summary>
///
public class CloseableThreadLocal<T> : IDisposable where T : class
{
// NOTE: Java has WeakReference<T>. This isn't available for .Net until 4.5 (according to msdn docs)
private ThreadLocal<WeakReference> t = new ThreadLocal<WeakReference>();
private IDictionary<Thread, T> hardRefs = new HashMap<Thread, T>();
private bool isDisposed;
public virtual T InitialValue()
{
return null;
}
public virtual T Get()
{
WeakReference weakRef = t.Get();
if (weakRef == null)
{
T iv = InitialValue();
if (iv != null)
{
Set(iv);
return iv;
}
else
return null;
}
else
{
return (T)weakRef.Get();
}
}
public virtual void Set(T @object)
{
//+-- For Debuging
if (CloseableThreadLocalProfiler.EnableCloseableThreadLocalProfiler == true)
{
lock (CloseableThreadLocalProfiler.Instances)
{
CloseableThreadLocalProfiler.Instances.Add(new WeakReference(@object));
}
}
//+--
t.Set(new WeakReference(@object));
lock (hardRefs)
{
//hardRefs[Thread.CurrentThread] = @object;
hardRefs.Add(Thread.CurrentThread, @object);
// Java's iterator can remove, .NET's cannot
var threadsToRemove = hardRefs.Keys.Where(thread => !thread.IsAlive).ToList();
// Purge dead threads
foreach (var thread in threadsToRemove)
{
hardRefs.Remove(thread);
}
}
}
[Obsolete("Use Dispose() instead")]
public virtual void Close()
{
Dispose();
}
public void Dispose()
{
Dispose(true);
}
protected virtual void Dispose(bool disposing)
{
if (isDisposed) return;
if (disposing)
{
// Clear the hard refs; then, the only remaining refs to
// all values we were storing are weak (unless somewhere
// else is still using them) and so GC may reclaim them:
hardRefs = null;
// Take care of the current thread right now; others will be
// taken care of via the WeakReferences.
if (t != null)
{
t.Remove();
}
t = null;
}
isDisposed = true;
}
}
internal static class CloseableThreadLocalExtensions
{
public static void Set<T>(this ThreadLocal<T> t, T val)
{
t.Value = val;
}
public static T Get<T>(this ThreadLocal<T> t)
{
return t.Value;
}
public static void Remove<T>(this ThreadLocal<T> t)
{
t.Dispose();
}
public static object Get(this WeakReference w)
{
return w.Target;
}
}
//// {{DIGY}}
//// To compile against Framework 2.0
//// Uncomment below class
//public class ThreadLocal<T> : IDisposable
//{
// [ThreadStatic]
// static SupportClass.WeakHashTable slots;
// void Init()
// {
// if (slots == null) slots = new SupportClass.WeakHashTable();
// }
// public T Value
// {
// set
// {
// Init();
// slots.Add(this, value);
// }
// get
// {
// Init();
// return (T)slots[this];
// }
// }
// public void Dispose()
// {
// if (slots != null) slots.Remove(this);
// }
//}
}
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