mcs/class/System.ComponentModel.Composition/src/ComponentModel/Microsoft/Internal/Collections/ConditionalWeakTable.cs

   1 // -----------------------------------------------------------------------\r
   2 // Copyright (c) Microsoft Corporation.  All rights reserved.\r
   3 // -----------------------------------------------------------------------\r
   4 #if !CLR40\r
   5 using System;\r
   6 using System.Collections;\r
   7 using System.Collections.Generic;\r
   8 using System.Linq;\r
   9 using Microsoft.Internal;\r
  10 using Microsoft.Internal.Collections;\r
  11 \r
  12 namespace Microsoft.Internal.Collections\r
  13 {\r
  14     // This is a broken implementation of ConditionalWeakTable that allows us\r
  15     // to compile and work on versions of .Net eariler then 4.0. This class is\r
  16     // broken when there are circular dependencies between keys and values, which\r
  17     // can only be fixed by using some specific CLR 4.0 features.\r
  18     // For code samples of the broken behavior see ConditionalWeakTableTests.cs.\r
  19     internal class ConditionalWeakTable<TKey, TValue> \r
  20         where TKey : class\r
  21         where TValue : class\r
  22     {\r
  23         private readonly Dictionary<object, TValue> _table;\r
  24         private int _capacity = 4;\r
  25 \r
  26         public ConditionalWeakTable()\r
  27         {\r
  28             this._table = new Dictionary<object, TValue>();\r
  29         }\r
  30 \r
  31         public void Add(TKey key, TValue value)\r
  32         {\r
  33             CleanupDeadReferences();\r
  34             this._table.Add(CreateWeakKey(key), value);\r
  35         }\r
  36 \r
  37         public bool Remove(TKey key)\r
  38         {\r
  39             return this._table.Remove(key);\r
  40         }\r
  41 \r
  42         public bool TryGetValue(TKey key, out TValue value)\r
  43         {\r
  44             return this._table.TryGetValue(key, out value);\r
  45         }\r
  46 \r
  47         private void CleanupDeadReferences()\r
  48         {\r
  49             if (this._table.Count < _capacity)\r
  50             {\r
  51                 return;\r
  52             }\r
  53 \r
  54             object[] deadKeys = this._table.Keys\r
  55                 .Where(weakRef => !((EquivalentWeakReference)weakRef).IsAlive).ToArray();\r
  56 \r
  57             foreach (var deadKey in deadKeys)\r
  58             {\r
  59                 this._table.Remove(deadKey);\r
  60             }\r
  61 \r
  62             if (this._table.Count >= _capacity)\r
  63             {\r
  64                 _capacity *= 2;\r
  65             }\r
  66         }\r
  67 \r
  68         private static object CreateWeakKey(TKey key)\r
  69         {\r
  70             return new EquivalentWeakReference(key);\r
  71         }\r
  72 \r
  73         private class EquivalentWeakReference\r
  74         {\r
  75             private readonly WeakReference _weakReference;\r
  76             private readonly int _hashCode;\r
  77 \r
  78             public EquivalentWeakReference(object obj)\r
  79             {\r
  80                 this._hashCode = obj.GetHashCode();\r
  81                 this._weakReference = new WeakReference(obj);\r
  82             }\r
  83 \r
  84             public bool IsAlive\r
  85             {\r
  86                 get\r
  87                 {\r
  88                     return this._weakReference.IsAlive;\r
  89                 }\r
  90             }\r
  91 \r
  92             public override bool Equals(object obj)\r
  93             {\r
  94                 EquivalentWeakReference weakRef = obj as EquivalentWeakReference;\r
  95 \r
  96                 if (weakRef != null)\r
  97                 {\r
  98                     obj = weakRef._weakReference.Target;\r
  99                 }\r
 100 \r
 101                 if (obj == null)\r
 102                 {\r
 103                     return base.Equals(weakRef);\r
 104                 }\r
 105                 \r
 106                 return object.Equals(this._weakReference.Target, obj);\r
 107             }\r
 108 \r
 109             public override int GetHashCode()\r
 110             {\r
 111                 return this._hashCode;\r
 112             }\r
 113         }\r
 114     }\r
 115 }\r
 116 #endif