mcs/class/corlib/System.Threading/LazyInitializer.cs

   1 //
   2 // LazyInitializer.cs
   3 //
   4 // Authors:
   5 //       Jérémie "Garuma" Laval <jeremie.laval@gmail.com>
   6 //       Marek Safar (marek.safar@gmail.com)
   7 //
   8 // Copyright (c) 2009 Jérémie "Garuma" Laval
   9 // Copyright 2011 Xamarin, Inc (http://www.xamarin.com)
  10 //
  11 // Permission is hereby granted, free of charge, to any person obtaining a copy
  12 // of this software and associated documentation files (the "Software"), to deal
  13 // in the Software without restriction, including without limitation the rights
  14 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  15 // copies of the Software, and to permit persons to whom the Software is
  16 // furnished to do so, subject to the following conditions:
  17 //
  18 // The above copyright notice and this permission notice shall be included in
  19 // all copies or substantial portions of the Software.
  20 //
  21 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  22 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  23 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  24 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  25 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  26 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  27 // THE SOFTWARE.
  28
  29 #if NET_4_0
  30
  31 namespace System.Threading
  32 {
  33         public static class LazyInitializer
  34         {
  35                 public static T EnsureInitialized<T> (ref T target) where T : class
  36                 {
  37                         return target ?? EnsureInitialized (ref target, GetDefaultCtorValue<T>);
  38                 }
  39
  40                 public static T EnsureInitialized<T> (ref T target, Func<T> valueFactory) where T : class
  41                 {
  42                         if (target == null) {
  43                                 var value = valueFactory ();
  44                                 if (value == null)
  45                                         throw new InvalidOperationException ();
  46
  47                                 Interlocked.CompareExchange (ref target, value, null);
  48                         }
  49
  50                         return target;
  51                 }
  52
  53                 public static T EnsureInitialized<T> (ref T target, ref bool initialized, ref object syncLock)
  54                 {
  55                         return EnsureInitialized (ref target, ref initialized, ref syncLock, GetDefaultCtorValue<T>);
  56                 }
  57
  58                 public static T EnsureInitialized<T> (ref T target, ref bool initialized, ref object syncLock, Func<T> valueFactory)
  59                 {
  60                         if (initialized)
  61                                 return target;
  62
  63                         if (syncLock == null)
  64                                 Interlocked.CompareExchange (ref syncLock, new object (), null);
  65
  66                         lock (syncLock) {
  67                                 if (initialized)
  68                                         return target;
  69
  70                                 initialized = true;
  71                                 Thread.MemoryBarrier ();
  72                                 target = valueFactory ();
  73                         }
  74
  75                         return target;
  76                 }
  77
  78                 static T GetDefaultCtorValue<T> ()
  79                 {
  80                         try {
  81                                 return Activator.CreateInstance<T> ();
  82                         } catch {
  83                                 throw new MissingMemberException ("The type being lazily initialized does not have a "
  84                                                                   + "public, parameterless constructor.");
  85                         }
  86                 }
  87         }
  88 }
  89 #endif