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The Labs \ Source Viewer \ SSCLI \ System.Threading \ CancellationSignal

SSCLI
  1. // ==++==
  2. //
  3. //
  4. // Copyright (c) 2006 Microsoft Corporation. All rights reserved.
  5. //
  6. // The use and distribution terms for this software are contained in the file
  7. // named license.txt, which can be found in the root of this distribution.
  8. // By using this software in any fashion, you are agreeing to be bound by the
  9. // terms of this license.
  10. //
  11. // You must not remove this notice, or any other, from this software.
  12. //
  13. //
  14. // ==--==
  15. /*============================================================
  16. **
  17. ** Class:  CancellationSignal
  18. **
  19. **
  20. ** Purpose: Defines an identifier to ensure you can only
  21. ** cancel synchronous IO requests that you were expecting to
  22. ** cancel.
  23. **
  24. **
  25. ===========================================================*/
  27. using System.IO;
  28. using System.Security.Permissions;
  29. using System.Collections.Generic;
  30. using System.Runtime.ConstrainedExecution;
  31. using Microsoft.Win32;
  33. namespace System.Threading
  34. {
  35.    
  36.    
  37.     public sealed class CancellationSignal
  38.     {
  39.         // Warning - Thread contains a stack of CancellationSignals, which
  40.         // places a restriction on this class. All types used within a
  41.         // CancellationSignal must be AppDomain-agile. Otherwise, we will
  42.         // bleed objects across appdomains, just as we do with CultureInfo
  43.         // today. Be very careful about adding new members here. We've
  44.         // sealed the class to prevent users from accidentally causing this
  45.         // problem for themselves in subclasses of CancellationSignal.
  46.         private Thread _thread;
  47.         private bool _cancelable;
  48.         private bool _wasCancelRequested;
  49.        
  50.         private static bool SupportsCancelSyncIOChecked;
  51.         private static bool OSSupportsCancelSyncIO;
  52.        
  53.         [ReliabilityContract(Consistency.MayCorruptInstance, Cer.MayFail)]
  54.         public CancellationSignal()
  55.         {
  56.             _cancelable = true;
  57.         }
  58.        
  59.         [ReliabilityContract(Consistency.MayCorruptInstance, Cer.MayFail)]
  60.         internal CancellationSignal(bool cancelable)
  61.         {
  62.             _cancelable = cancelable;
  63.         }
  64.        
  65.         [HostProtection(ExternalThreading = true)]
  66.         [SecurityPermission(SecurityAction.LinkDemand, UnmanagedCode = true)]
  67.         public void Cancel()
  68.         {
  69.             _wasCancelRequested = true;
  70.             throw new PlatformNotSupportedException();
  71.         }
  72.        
  73.         private static void CheckSupportsCancelSyncIO()
  74.         {
  75.             OSSupportsCancelSyncIO = false;
  76.             SupportsCancelSyncIOChecked = true;
  77.         }
  78.        
  79.         // To allow CPU-intensive tasks to use our cancellation model to
  80.         // opt into cancellation via polling. We could also use this in
  81.         // select places to help avoid races inherent in the OS's
  82.         // cancellation model, such as attempting to cancel CopyFile while
  83.         // it is in the middle of some CPU-intensive calculation instead of
  84.         // blocked waiting for IO.
  85.         // Note that if you cancel one region, it should cancel any nested
  86.         // cancellable regions. See Cancel for this logic.
  87.         public bool CancelRequested {
  88.             [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
  89.             get { return _wasCancelRequested; }
  90.         }
  91.        
  92.         internal Thread Thread {
  93.             [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
  94.             get { return _thread; }
  95.             [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
  96.             set {
  97.                 if (_thread != null && value != null)
  98.                     throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_CancellationSignalReuse"));
  99.                 _thread = value;
  100.             }
  101.         }
  102.     }
  103. }

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