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// -----------------------------------------------------------------------
// Copyright (c) Microsoft Corporation. All rights reserved.
// -----------------------------------------------------------------------
#if !CLR40
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using Microsoft.Internal;
using Microsoft.Internal.Collections;
namespace Microsoft.Internal.Collections
{
// This is a broken implementation of ConditionalWeakTable that allows us
// to compile and work on versions of .Net eariler then 4.0. This class is
// broken when there are circular dependencies between keys and values, which
// can only be fixed by using some specific CLR 4.0 features.
// For code samples of the broken behavior see ConditionalWeakTableTests.cs.
internal class ConditionalWeakTable<TKey, TValue>
where TKey : class
where TValue : class
{
private readonly Dictionary<object, TValue> _table;
private int _capacity = 4;
public ConditionalWeakTable()
{
this._table = new Dictionary<object, TValue>();
}
public void Add(TKey key, TValue value)
{
CleanupDeadReferences();
this._table.Add(CreateWeakKey(key), value);
}
public bool Remove(TKey key)
{
return this._table.Remove(key);
}
public bool TryGetValue(TKey key, out TValue value)
{
return this._table.TryGetValue(key, out value);
}
private void CleanupDeadReferences()
{
if (this._table.Count < _capacity)
{
return;
}
object[] deadKeys = this._table.Keys
.Where(weakRef => !((EquivalentWeakReference)weakRef).IsAlive).ToArray();
foreach (var deadKey in deadKeys)
{
this._table.Remove(deadKey);
}
if (this._table.Count >= _capacity)
{
_capacity *= 2;
}
}
private static object CreateWeakKey(TKey key)
{
return new EquivalentWeakReference(key);
}
private class EquivalentWeakReference
{
private readonly WeakReference _weakReference;
private readonly int _hashCode;
public EquivalentWeakReference(object obj)
{
this._hashCode = obj.GetHashCode();
this._weakReference = new WeakReference(obj);
}
public bool IsAlive
{
get
{
return this._weakReference.IsAlive;
}
}
public override bool Equals(object obj)
{
EquivalentWeakReference weakRef = obj as EquivalentWeakReference;
if (weakRef != null)
{
obj = weakRef._weakReference.Target;
}
if (obj == null)
{
return base.Equals(weakRef);
}
return object.Equals(this._weakReference.Target, obj);
}
public override int GetHashCode()
{
return this._hashCode;
}
}
}
}
#endif
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