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1 using System;
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2 using System.Threading;
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3 using Implab.Parallels;
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4
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5 namespace Implab {
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6 public class CancellationToken : ICancellationToken {
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7 const int CANCEL_NOT_REQUESTED = 0;
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8 const int CANCEL_REQUESTING = 1;
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9 const int CANCEL_REQUESTED = 2;
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10
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11 volatile int m_state = CANCEL_NOT_REQUESTED;
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12
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13 Action<Exception> m_handler;
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14
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15 Parallels.SimpleAsyncQueue<Action<Exception>> m_handlers;
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16
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17 public bool IsCancellationRequested {
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18 get { return m_state == CANCEL_REQUESTED; }
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19 }
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20
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21 public Exception CancellationReason {
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22 get; set;
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23 }
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24
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25 public void CancellationRequested(Action<Exception> handler) {
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26 Safe.ArgumentNotNull(handler, nameof(handler));
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27 if (IsCancellationRequested) {
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28 handler(CancellationReason);
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29 } else {
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30 EnqueueHandler(handler);
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31 if (IsCancellationRequested && TryDequeueHandler(out handler))
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32 handler(CancellationReason);
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33 }
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34 }
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35
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36 bool TryDequeueHandler(out Action<Exception> handler) {
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37 handler = Interlocked.Exchange(ref m_handler, null);
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38 if (handler != null)
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39 return true;
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40 else if (m_handlers != null)
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41 return m_handlers.TryDequeue(out handler);
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42 else
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43 return false;
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44 }
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45
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46 void EnqueueHandler(Action<Exception> handler) {
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47 if (Interlocked.CompareExchange(ref m_handler, handler, null) != null) {
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48 if (m_handlers == null)
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49 // compare-exchange will fprotect from loosing already created queue
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50 Interlocked.CompareExchange(ref m_handlers, new SimpleAsyncQueue<Action<Exception>>(), null);
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51 m_handlers.Enqueue(handler);
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52 }
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53 }
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54
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55 void RequestCancellation(Exception reason) {
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56 if (Interlocked.CompareExchange(ref m_state, CANCEL_REQUESTING, CANCEL_NOT_REQUESTED) == CANCEL_NOT_REQUESTED) {
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57 if (reason == null)
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58 reason = new OperationCanceledException();
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59 CancellationReason = reason;
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60 m_state = CANCEL_REQUESTED;
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61 }
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62 }
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63
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64 }
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65 } |
