mcs/class/corlib/System.Runtime.CompilerServices/YieldAwaitable.cs

   1 //
   2 // YieldAwaitable.cs
   3 //
   4 // Authors:
   5 //      Marek Safar  <marek.safar@gmail.com>
   6 //
   7 // Copyright (C) 2011 Novell, Inc (http://www.novell.com)
   8 // Copyright (C) 2011 Xamarin, Inc (http://www.xamarin.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 #if NET_4_5
  31
  32 using System.Threading;
  33 using System.Threading.Tasks;
  34
  35 namespace System.Runtime.CompilerServices
  36 {
  37         public struct YieldAwaitable
  38         {
  39                 public struct YieldAwaiter : ICriticalNotifyCompletion
  40                 {
  41                         public bool IsCompleted {
  42                                 get {
  43                                         return false;
  44                                 }
  45                         }
  46
  47                         public void OnCompleted (Action continuation)
  48                         {
  49                                 OnCompleted (continuation, false);
  50                         }
  51
  52                         public void UnsafeOnCompleted (Action continuation)
  53                         {
  54                                 OnCompleted (continuation, true);
  55                         }
  56
  57                         void OnCompleted (Action continuation, bool isUnsafe)
  58                         {
  59                                 if (continuation == null)
  60                                         throw new ArgumentNullException ("continuation");
  61
  62                                 var ctx = SynchronizationContext.Current;
  63                                 if (ctx != null) {
  64                                         ctx.Post (l => ((Action) l) (), continuation);
  65                                         return;
  66                                 }
  67
  68                                 if (TaskScheduler.Current == TaskScheduler.Default) {
  69                                         //
  70                                         // Pass continuation as an argument to avoid allocating
  71                                         // hoisting class
  72                                         //
  73                                         WaitCallback callBack = l => ((Action) l) ();
  74                                         if (isUnsafe) {
  75                                                 ThreadPool.UnsafeQueueUserWorkItem (callBack, continuation);
  76                                         } else {
  77                                                 ThreadPool.QueueUserWorkItem (callBack, continuation);
  78                                         }
  79                                         return;
  80                                 }
  81
  82                                 new Task (continuation).Start (TaskScheduler.Current);
  83                         }
  84
  85                         public void GetResult ()
  86                         {
  87                         }
  88                 }
  89
  90                 public YieldAwaitable.YieldAwaiter GetAwaiter ()
  91                 {
  92                         return new YieldAwaiter ();
  93                 }
  94         }
  95 }
  96
  97 #endif