class/corlib/System.Runtime.Serialization/ObjectIDGenerator.cs

   1 //
   2 // System.Runtime.Serialization.ObjectIDGenerator.cs
   3 //
   4 // Author: Duncan Mak  (duncan@ximian.com)
   5 //         Lluis Sanchez (lsg@ctv.es)
   6 //
   7 // (C) Ximian, Inc.
   8 // Copyright (C) 2004,2006 Novell, Inc (http://www.novell.com)
   9 //
  10 // Permission is hereby granted, free of charge, to any person obtaining
  11 // a copy of this software and associated documentation files (the
  12 // "Software"), to deal in the Software without restriction, including
  13 // without limitation the rights to use, copy, modify, merge, publish,
  14 // distribute, sublicense, and/or sell copies of the Software, and to
  15 // permit persons to whom the Software is furnished to do so, subject to
  16 // the following conditions:
  17 //
  18 // The above copyright notice and this permission notice shall be
  19 // included in all copies or substantial portions of the Software.
  20 //
  21 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  22 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  23 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  24 // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  25 // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  26 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  27 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  28 //
  29
  30 using System.Collections;
  31
  32 namespace System.Runtime.Serialization
  33 {
  34         [Serializable]
  35         [MonoTODO ("Serialization format not compatible with.NET")]
  36         [System.Runtime.InteropServices.ComVisibleAttribute (true)]
  37         public class ObjectIDGenerator
  38         {
  39                 // Private field
  40                 Hashtable table;
  41                 long current; // this is the current ID, starts at 1
  42                 static InstanceComparer comparer = new InstanceComparer ();
  43
  44
  45                 // ObjectIDGenerator must generate a new id for each object instance.
  46                 // If two objects have the same state (i.e. the method Equals() returns true),
  47                 // each one should have a different id.
  48                 // Thus, the object instance cannot be directly used as key of the hashtable.
  49                 // InstanceComparer compares object references instead of object content
  50                 // (unless the object is inmutable, like strings).
  51
  52                 class InstanceComparer: IComparer, IHashCodeProvider
  53                 {
  54                         int IComparer.Compare (object o1, object o2)
  55                         {
  56                                 if (o1 is string)
  57                                         return o1.Equals(o2) ? 0 : 1;
  58                                 else
  59                                         return (o1 == o2) ? 0 : 1;
  60                         }
  61
  62                         int IHashCodeProvider.GetHashCode (object o)
  63                         {
  64                                 return object.InternalGetHashCode (o);
  65                         }
  66                 }
  67
  68                 // constructor
  69                 public ObjectIDGenerator ()
  70                         : base ()
  71                 {
  72                         table = new Hashtable (comparer, comparer);
  73                         current = 1;
  74                 }
  75
  76                 // Methods
  77                 public virtual long GetId (object obj, out bool firstTime)
  78                 {
  79                         if (obj == null)
  80                                 throw new ArgumentNullException ("obj");
  81
  82                         object val = table [obj];
  83
  84                         if (val != null) {
  85                                 firstTime = false;
  86                                 return (long) val;
  87
  88                         } else {
  89                                 firstTime = true;
  90                                 table.Add (obj, current);
  91                                 return current ++;
  92                         }
  93                 }
  94
  95                 public virtual long HasId (object obj, out bool firstTime)
  96                 {
  97                         if (obj == null)
  98                                 throw new ArgumentNullException ("obj");
  99
 100                         object val = table [obj];
 101
 102                         if (val != null) {
 103                                 firstTime = false;
 104                                 return (long) val;
 105
 106                         } else {
 107                                 firstTime = true;
 108                                 return 0L; // 0 is the null ID
 109                         }
 110                 }
 111
 112                 internal long NextId
 113                 {
 114                         get { return current ++; }
 115                 }
 116         }
 117 }