mcs/class/corlib/System/WeakReference.cs

   1 //
   2 // System.WeakReference.cs
   3 //
   4 // Author:
   5 //   Ajay kumar Dwivedi (adwiv@yahoo.com)
   6 //
   7
   8 //
   9 // Copyright (C) 2004 Novell, Inc (http://www.novell.com)
  10 //
  11 // Permission is hereby granted, free of charge, to any person obtaining
  12 // a copy of this software and associated documentation files (the
  13 // "Software"), to deal in the Software without restriction, including
  14 // without limitation the rights to use, copy, modify, merge, publish,
  15 // distribute, sublicense, and/or sell copies of the Software, and to
  16 // permit persons to whom the Software is furnished to do so, subject to
  17 // the following conditions:
  18 //
  19 // The above copyright notice and this permission notice shall be
  20 // included in all copies or substantial portions of the Software.
  21 //
  22 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  23 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  24 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  25 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  26 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  27 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  28 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  29 //
  30
  31 using System.Runtime.Serialization;
  32 using System.Runtime.InteropServices;
  33
  34 namespace System
  35 {
  36         [Serializable]
  37         public class WeakReference : ISerializable
  38         {
  39                 //Fields
  40                 private bool isLongReference;
  41                 private GCHandle gcHandle;
  42
  43                 // Helper method for constructors
  44                 //Should not be called from any other method.
  45                 private void AllocateHandle (Object target)
  46                 {
  47                         if (isLongReference) {
  48                                 gcHandle = GCHandle.Alloc (target, GCHandleType.WeakTrackResurrection);
  49                         }
  50                         else {
  51                                 gcHandle = GCHandle.Alloc (target, GCHandleType.Weak);
  52                         }
  53                 }
  54
  55                 //Constructors
  56                 public WeakReference (object target)
  57                         : this (target, false)
  58                 {
  59                 }
  60
  61                 public WeakReference (object target, bool trackResurrection)
  62                 {
  63                         isLongReference = trackResurrection;
  64                         AllocateHandle (target);
  65                 }
  66
  67                 protected WeakReference (SerializationInfo info, StreamingContext context)
  68                 {
  69                         if (info == null)
  70                                 throw new ArgumentNullException ("info");
  71
  72                         isLongReference = info.GetBoolean ("TrackResurrection");
  73                         Object target = info.GetValue ("TrackedObject", typeof (System.Object));
  74
  75                         AllocateHandle (target);
  76                 }
  77
  78                 // Properties
  79                 public virtual bool IsAlive {
  80                         get {
  81                                 //Target property takes care of the exception
  82                                 return (Target != null);
  83                         }
  84                 }
  85
  86                 public virtual object Target {
  87                         get {
  88                                 //Exception is thrown by gcHandle's Target
  89                                 return gcHandle.Target;
  90                         }
  91                         set
  92                         {
  93                                 gcHandle.Target = value;
  94                         }
  95                 }
  96
  97                 public virtual bool TrackResurrection {
  98                         get {
  99                                 return isLongReference;
 100                         }
 101                 }
 102
 103                 //Methods
 104                 ~WeakReference ()
 105                 {
 106                         gcHandle.Free ();
 107                 }
 108
 109                 public virtual void GetObjectData (SerializationInfo info, StreamingContext context)
 110                 {
 111                         if (info == null)
 112                                 throw new ArgumentNullException ("info");
 113
 114                         info.AddValue ("TrackResurrection", TrackResurrection);
 115
 116                         try {
 117                                 info.AddValue ("TrackedObject", Target);
 118                         } catch (Exception) {
 119                                 info.AddValue ("TrackedObject", null);
 120                         }
 121                 }
 122         }
 123 }