mcs/class/corlib/System/Lazy.cs

   1 //
   2 // Lazy.cs
   3 //
   4 // Authors:
   5 //  Zoltan Varga (vargaz@gmail.com)
   6 //  Marek Safar (marek.safar@gmail.com)
   7 //
   8 // Copyright (C) 2009 Novell
   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 #if NET_4_0
  31
  32 using System;
  33 using System.Runtime.Serialization;
  34 using System.Runtime.InteropServices;
  35 using System.Security.Permissions;
  36 using System.Threading;
  37 using System.Diagnostics;
  38
  39 namespace System
  40 {
  41         [SerializableAttribute]
  42         [ComVisibleAttribute(false)]
  43         [HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization = true, ExternalThreading = true)]
  44         [DebuggerDisplay ("ThreadSafetyMode={Mode}, IsValueCreated={IsValueCreated}, IsValueFaulted={IsValueFaulted}, Value={ValueForDebugDisplay}")]
  45         public class Lazy<T>
  46         {
  47                 T value;
  48                 Func<T> factory;
  49                 object monitor;
  50                 Exception exception;
  51                 LazyThreadSafetyMode mode;
  52                 bool inited;
  53
  54                 public Lazy ()
  55                         : this (LazyThreadSafetyMode.ExecutionAndPublication)
  56                 {
  57                 }
  58
  59                 public Lazy (Func<T> valueFactory)
  60                         : this (valueFactory, LazyThreadSafetyMode.ExecutionAndPublication)
  61                 {
  62                 }
  63
  64                 public Lazy (bool isThreadSafe)
  65                         : this (Activator.CreateInstance<T>, isThreadSafe ? LazyThreadSafetyMode.ExecutionAndPublication : LazyThreadSafetyMode.None)
  66                 {
  67                 }
  68
  69                 public Lazy (Func<T> valueFactory, bool isThreadSafe)
  70                         : this (valueFactory, isThreadSafe ? LazyThreadSafetyMode.ExecutionAndPublication : LazyThreadSafetyMode.None)
  71                 {
  72                 }
  73
  74                 public Lazy (LazyThreadSafetyMode mode)
  75                         : this (Activator.CreateInstance<T>, mode)
  76                 {
  77                 }
  78
  79
  80
  81                 public Lazy (Func<T> valueFactory, LazyThreadSafetyMode mode)
  82                 {
  83                         if (valueFactory == null)
  84                                 throw new ArgumentNullException ("valueFactory");
  85                         this.factory = valueFactory;
  86                         if (mode != LazyThreadSafetyMode.None)
  87                                 monitor = new object ();
  88                         this.mode = mode;
  89                 }
  90
  91                 // Don't trigger expensive initialization
  92                 [DebuggerBrowsable (DebuggerBrowsableState.Never)]
  93                 public T Value {
  94                         get {
  95                                 if (inited)
  96                                         return value;
  97                                 if (exception != null)
  98                                         throw exception;
  99
 100                                 return InitValue ();
 101                         }
 102                 }
 103
 104                 T InitValue ()
 105                 {
 106                         Func<T> init_factory;
 107                         T v;
 108
 109                         switch (mode) {
 110                         case LazyThreadSafetyMode.None:
 111                                 init_factory = factory;
 112                                 if (init_factory == null)
 113                                         throw exception = new InvalidOperationException ("The initialization function tries to access Value on this instance");
 114                                 try {
 115                                         factory = null;
 116                                         v = init_factory ();
 117                                         value = v;
 118                                         Thread.MemoryBarrier ();
 119                                         inited = true;
 120                                 } catch (Exception ex) {
 121                                         exception = ex;
 122                                         throw;
 123                                 }
 124                                 break;
 125
 126                         case LazyThreadSafetyMode.PublicationOnly:
 127                                 init_factory = factory;
 128
 129                                 //exceptions are ignored
 130                                 if (init_factory != null)
 131                                         v = init_factory ();
 132                                 else
 133                                         v = default (T);
 134
 135                                 lock (monitor) {
 136                                         if (inited)
 137                                                 return value;
 138                                         value = v;
 139                                         Thread.MemoryBarrier ();
 140                                         inited = true;
 141                                         factory = null;
 142                                 }
 143                                 break;
 144
 145                         case LazyThreadSafetyMode.ExecutionAndPublication:
 146                                 lock (monitor) {
 147                                         if (inited)
 148                                                 return value;
 149
 150                                         if (factory == null)
 151                                                 throw exception = new InvalidOperationException ("The initialization function tries to access Value on this instance");
 152
 153                                         init_factory = factory;
 154                                         try {
 155                                                 factory = null;
 156                                                 v = init_factory ();
 157                                                 value = v;
 158                                                 Thread.MemoryBarrier ();
 159                                                 inited = true;
 160                                         } catch (Exception ex) {
 161                                                 exception = ex;
 162                                                 throw;
 163                                         }
 164                                 }
 165                                 break;
 166
 167                         default:
 168                                 throw new InvalidOperationException ("Invalid LazyThreadSafetyMode " + mode);
 169                         }
 170
 171                         return value;
 172                 }
 173
 174                 public bool IsValueCreated {
 175                         get {
 176                                 return inited;
 177                         }
 178                 }
 179
 180                 public override string ToString ()
 181                 {
 182                         if (inited)
 183                                 return value.ToString ();
 184                         else
 185                                 return "Value is not created";
 186                 }
 187         }
 188 }
 189
 190 #endif