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using System;
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using System.Threading;
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using Implab.Parallels;
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namespace Implab {
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public class CancellationToken : ICancellationToken {
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const int CANCEL_NOT_REQUESTED = 0;
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const int CANCEL_REQUESTING = 1;
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const int CANCEL_REQUESTED = 2;
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volatile int m_state = CANCEL_NOT_REQUESTED;
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Action<Exception> m_handler;
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Parallels.SimpleAsyncQueue<Action<Exception>> m_handlers;
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public bool IsCancellationRequested {
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get { return m_state == CANCEL_REQUESTED; }
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}
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public Exception CancellationReason {
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get; set;
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}
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public void CancellationRequested(Action<Exception> handler) {
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Safe.ArgumentNotNull(handler, nameof(handler));
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if (IsCancellationRequested) {
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handler(CancellationReason);
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} else {
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EnqueueHandler(handler);
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if (IsCancellationRequested && TryDequeueHandler(out handler))
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handler(CancellationReason);
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}
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}
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bool TryDequeueHandler(out Action<Exception> handler) {
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handler = Interlocked.Exchange(ref m_handler, null);
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if (handler != null)
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return true;
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else if (m_handlers != null)
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return m_handlers.TryDequeue(out handler);
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else
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return false;
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}
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void EnqueueHandler(Action<Exception> handler) {
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if (Interlocked.CompareExchange(ref m_handler, handler, null) != null) {
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if (m_handlers == null)
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// compare-exchange will fprotect from loosing already created queue
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Interlocked.CompareExchange(ref m_handlers, new SimpleAsyncQueue<Action<Exception>>(), null);
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m_handlers.Enqueue(handler);
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}
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}
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void RequestCancellation(Exception reason) {
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if (Interlocked.CompareExchange(ref m_state, CANCEL_REQUESTING, CANCEL_NOT_REQUESTED) == CANCEL_NOT_REQUESTED) {
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if (reason == null)
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reason = new OperationCanceledException();
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CancellationReason = reason;
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m_state = CANCEL_REQUESTED;
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}
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}
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}
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}
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