mcs/class/System.Threading.Tasks.Dataflow/System.Threading.Tasks.Dataflow/OutputAvailableBlock.cs

   1 // OutputAvailableBlock.cs
   2 //
   3 // Copyright (c) 2011 Jérémie "garuma" Laval
   4 // Copyright (c) 2012 Petr Onderka
   5 //
   6 // Permission is hereby granted, free of charge, to any person obtaining a copy
   7 // of this software and associated documentation files (the "Software"), to deal
   8 // in the Software without restriction, including without limitation the rights
   9 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10 // copies of the Software, and to permit persons to whom the Software is
  11 // furnished to do so, subject to the following conditions:
  12 //
  13 // The above copyright notice and this permission notice shall be included in
  14 // all copies or substantial portions of the Software.
  15 //
  16 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  19 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22 // THE SOFTWARE.
  23
  24 namespace System.Threading.Tasks.Dataflow {
  25         /// <summary>
  26         /// This internal block is used by the <see cref="DataflowBlock.OutputAvailableAsync"/> methods
  27         /// to check for available items in an asynchronous way.
  28         /// </summary>
  29         class OutputAvailableBlock<TOutput> : ITargetBlock<TOutput> {
  30                 readonly TaskCompletionSource<bool> completion =
  31                         new TaskCompletionSource<bool> ();
  32                 IDisposable linkBridge;
  33                 CancellationTokenRegistration cancellationRegistration;
  34
  35                 public DataflowMessageStatus OfferMessage (
  36                         DataflowMessageHeader messageHeader, TOutput messageValue,
  37                         ISourceBlock<TOutput> source, bool consumeToAccept)
  38                 {
  39                         if (!messageHeader.IsValid)
  40                                 return DataflowMessageStatus.Declined;
  41
  42                         if (completion.Task.Status != TaskStatus.WaitingForActivation)
  43                                 return DataflowMessageStatus.DecliningPermanently;
  44
  45                         completion.TrySetResult (true);
  46                         CompletionSet ();
  47
  48                         return DataflowMessageStatus.DecliningPermanently;
  49                 }
  50
  51                 /// <summary>
  52                 /// Returns a Task that can be used to wait until output from a block is available.
  53                 /// </summary>
  54                 /// <param name="bridge">The disposable object returned by <see cref="ISourceBlock{TOutput}.LinkTo"/>.</param>
  55                 /// <param name="token">Cancellation token for this operation.</param>
  56                 public Task<bool> AsyncGet (IDisposable bridge, CancellationToken token)
  57                 {
  58                         linkBridge = bridge;
  59                         cancellationRegistration = token.Register (() =>
  60                         {
  61                                 completion.TrySetCanceled ();
  62                                 CompletionSet ();
  63                         });
  64
  65                         return completion.Task;
  66                 }
  67
  68                 /// <summary>
  69                 /// Called after the result has been set,
  70                 /// cleans up after this block.
  71                 /// </summary>
  72                 void CompletionSet ()
  73                 {
  74                         if (linkBridge != null) {
  75                                 linkBridge.Dispose ();
  76                                 linkBridge = null;
  77                         }
  78
  79                         cancellationRegistration.Dispose ();
  80                 }
  81
  82                 public Task Completion {
  83                         get { throw new NotSupportedException (); }
  84                 }
  85
  86                 public void Complete ()
  87                 {
  88                         completion.TrySetResult (false);
  89                         CompletionSet ();
  90                 }
  91
  92                 public void Fault (Exception exception)
  93                 {
  94                         Complete ();
  95                 }
  96         }
  97 }