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         public class Lazy<T>
  45         {
  46                 T value;
  47                 bool inited;
  48                 LazyThreadSafetyMode mode;
  49                 Func<T> factory;
  50                 object monitor;
  51                 Exception exception;
  52
  53                 public Lazy ()
  54                         : this (LazyThreadSafetyMode.ExecutionAndPublication)
  55                 {
  56                 }
  57
  58                 public Lazy (Func<T> valueFactory)
  59                         : this (valueFactory, LazyThreadSafetyMode.ExecutionAndPublication)
  60                 {
  61                 }
  62
  63                 public Lazy (bool isThreadSafe)
  64                         : this (() => Activator.CreateInstance<T> (), isThreadSafe ? LazyThreadSafetyMode.ExecutionAndPublication : LazyThreadSafetyMode.None)
  65                 {
  66                 }
  67
  68                 public Lazy (Func<T> valueFactory, bool isThreadSafe)
  69                         : this (valueFactory, isThreadSafe ? LazyThreadSafetyMode.ExecutionAndPublication : LazyThreadSafetyMode.None)
  70                 {
  71                 }
  72
  73                 public Lazy (LazyThreadSafetyMode mode)
  74                         : this (() => Activator.CreateInstance<T> (), mode)
  75                 {
  76                 }
  77
  78
  79
  80                 public Lazy (Func<T> valueFactory, LazyThreadSafetyMode mode)
  81                 {
  82                         if (valueFactory == null)
  83                                 throw new ArgumentNullException ("valueFactory");
  84                         this.factory = valueFactory;
  85                         if (mode != LazyThreadSafetyMode.None)
  86                                 monitor = new object ();
  87                         this.mode = mode;
  88                 }
  89
  90                 // Don't trigger expensive initialization
  91                 [DebuggerBrowsable (DebuggerBrowsableState.Never)]
  92                 public T Value {
  93                         get {
  94                                 if (inited)
  95                                         return value;
  96                                 if (exception != null)
  97                                         throw exception;
  98
  99                                 return InitValue ();
 100                         }
 101                 }
 102
 103                 T InitValue () {
 104                         switch (mode) {
 105                         case LazyThreadSafetyMode.None: {
 106                                 var init_factory = factory;
 107                                 if (init_factory == null)
 108                                         throw exception = new InvalidOperationException ("The initialization function tries to access Value on this instance");
 109                                 try {
 110                                         factory = null;
 111                                         T v = init_factory ();
 112                                         value = v;
 113                                         Thread.MemoryBarrier ();
 114                                         inited = true;
 115                                 } catch (Exception ex) {
 116                                         exception = ex;
 117                                         throw;
 118                                 }
 119                                 break;
 120                         }
 121                         case LazyThreadSafetyMode.PublicationOnly: {
 122                                 var init_factory = factory;
 123                                 T v;
 124
 125                                 //exceptions are ignored
 126                                 if (init_factory != null)
 127                                         v = init_factory ();
 128                                 else
 129                                         v = default (T);
 130
 131                                 lock (monitor) {
 132                                         if (inited)
 133                                                 return value;
 134                                         value = v;
 135                                         Thread.MemoryBarrier ();
 136                                         inited = true;
 137                                         factory = null;
 138                                 }
 139                                 break;
 140                         }
 141                         case LazyThreadSafetyMode.ExecutionAndPublication: {
 142                                 lock (monitor) {
 143                                         if (inited)
 144                                                 return value;
 145
 146                                         if (factory == null)
 147                                                 throw exception = new InvalidOperationException ("The initialization function tries to access Value on this instance");
 148
 149                                         var init_factory = factory;
 150                                         try {
 151                                                 factory = null;
 152                                                 T v = init_factory ();
 153                                                 value = v;
 154                                                 Thread.MemoryBarrier ();
 155                                                 inited = true;
 156                                         } catch (Exception ex) {
 157                                                 exception = ex;
 158                                                 throw;
 159                                         }
 160                                 }
 161                                 break;
 162                         }
 163                         default:
 164                                 throw new InvalidOperationException ("Invalid LazyThreadSafetyMode " + mode);
 165                         }
 166
 167                         if (monitor == null) {
 168                                 value = factory ();
 169                                 inited = true;
 170                         } else {
 171                                 lock (monitor) {
 172                                         if (inited)
 173                                                 return value;
 174
 175                                         if (factory == null)
 176                                                 throw new InvalidOperationException ("The initialization function tries to access Value on this instance");
 177
 178                                         var init_factory = factory;
 179                                         try {
 180                                                 factory = null;
 181                                                 T v = init_factory ();
 182                                                 value = v;
 183                                                 Thread.MemoryBarrier ();
 184                                                 inited = true;
 185                                         } catch {
 186                                                 factory = init_factory;
 187                                                 throw;
 188                                         }
 189                                 }
 190                         }
 191
 192                         return value;
 193                 }
 194
 195                 public bool IsValueCreated {
 196                         get {
 197                                 return inited;
 198                         }
 199                 }
 200
 201                 public override string ToString ()
 202                 {
 203                         if (inited)
 204                                 return value.ToString ();
 205                         else
 206                                 return "Value is not created";
 207                 }
 208         }
 209 }
 210
 211 #endif