CancellationState.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / System / Linq / Parallel / Scheduling / CancellationState.cs / 1305376 / CancellationState.cs
                        

                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
// 
// CancellationState.cs 
//
// [....] 
//
// A bag of cancellation-related items that are passed around as a group.
//
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- 

using System; 
using System.Collections.Generic; 
using System.Threading;
 
namespace System.Linq.Parallel
{
    internal class CancellationState
    { 
        // a cancellation signal that can be set internally to prompt early query termination.
        internal CancellationTokenSource InternalCancellationTokenSource; 
 
        // the external cancellationToken that the user sets to ask for the query to terminate early.
        // this has to be tracked explicitly so that an OCE(externalToken) can be thrown as the query 
        // execution unravels.
        internal CancellationToken ExternalCancellationToken;

        // A combined token Source for internal/external cancellation, defining the total cancellation state. 
        internal CancellationTokenSource MergedCancellationTokenSource;
 
        // A combined token for internal/external cancellation, defining the total cancellation state. 
        internal CancellationToken MergedCancellationToken
        { 
            get
            {
                if( MergedCancellationTokenSource != null)
                    return MergedCancellationTokenSource.Token; 
                else
                    return new CancellationToken(false); 
            } 
        }
 
        // A shared boolean flag to track whether a query-opening-enumerator dispose has occured.
        internal Shared TopLevelDisposedFlag;

        internal CancellationState(CancellationToken externalCancellationToken) 
        {
            ExternalCancellationToken = externalCancellationToken; 
            TopLevelDisposedFlag = new Shared(false); //it would always be initialised to false, so no harm doing it here and avoid #if around constructors. 
        }
 
        /// 
        /// Poll frequency (number of loops per cancellation check) for situations where per-1-loop testing is too high an overhead.
        /// 
        internal const int POLL_INTERVAL = 63;  //must be of the form (2^n)-1. 

        // The two main situations requiring POLL_INTERVAL are: 
        //    1. inner loops of sorting/merging operations 
        //    2. tight loops that perform very little work per MoveNext call.
        // Testing has shown both situations have similar requirements and can share the same constant for polling interval. 
        //
        // Because the poll checks are per-N loops, if there are delays in user code, they may affect cancellation timeliness.
        // Guidance is that all user-delegates should perform cancellation checks at least every 1ms.
        // 
        // Inner loop code should poll once per n loop, typically via:
        // if ((i++ & CancellationState.POLL_INTERVAL) == 0) 
        //     CancellationState.ThrowIfCanceled(m_cancellationToken); 
        // (Note, this only behaves as expected if FREQ is of the form (2^n)-1
 
        /// 
        /// Throws an OCE if the merged token has been canceled.
        /// 
        /// A token to check for cancelation. 
        internal static void ThrowIfCanceled(CancellationToken token)
        { 
            if (token.IsCancellationRequested) 
                throw new OperationCanceledException(token);
        } 

        // Test if external cancellation was requested and occured, and if so throw a standardize OCE with standardized message
        internal static void ThrowWithStandardMessageIfCanceled(CancellationToken externalCancellationToken)
        { 
            if (externalCancellationToken.IsCancellationRequested)
            { 
                string oceMessage = SR.GetString(SR.PLINQ_ExternalCancellationRequested); 
                throw new OperationCanceledException(oceMessage, externalCancellationToken);
            } 
        }
    }
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.

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