使用链接的CancellationTokenSource时如何解开CancellationToken的最佳实践

Question

我目前在我的应用中采用.NET Cancellation Framework 。 看来我需要CancellationTokenSource使用链接的CancellationTokenSource ，并且发现在每个匹配的catch中“解包” OperationCanceledException很麻烦，因此它包含正确的CancellationToken 。 我想问一下：

1. 是否有任何现成的解决方案可以简化这种情况？
2. 什么是与之相关的“最佳实践”？

我的问题是关于.NET 4的。我还附加了代码样本，该样本显示了我在说什么：

Using linkedCts = CancellationTokenSource.CreateLinkedTokenSource(externalCancelToken, internalCancelToken)
    Try
        myRequest.Dispatch(linkedCts.Token)

    Catch ex As WebException When ex.Status = WebExceptionStatus.RequestCanceled
        If externalCancelToken.IsCancellationRequested Then
            Throw New OperationCanceledException(externalCancelToken)
        ElseIf internalCancelToken.IsCancellationRequested Then
            Throw New OperationCanceledException(internalCancelToken)
        Else
            Throw
        End If

    Catch ex As OperationCanceledException
        If ex.CancellationToken = linkedCts.Token Then
            If externalCancelToken.IsCancellationRequested Then
                Throw New OperationCanceledException(Nothing, ex, externalCancelToken)
            ElseIf internalCancelToken.IsCancellationRequested Then
                Throw New OperationCanceledException(Nothing, ex, internalCancelToken)
            End If
        End If

    End Try
End Using

Answer 1

我试图用谷歌搜索一些想法，但一无所获。 因此，我为链接的CancellationTokenSource -es提出了以下包装：

Imports System.Threading


Namespace Threading

    Public Class LinkedCancellationTokenSource
        Implements IDisposable


        Public ReadOnly Property Token As CancellationToken
            Get
                Return Me.internalSource.Token
            End Get
        End Property


        Public ReadOnly Property IsCancellationRequested As Boolean
            Get
                Return Me.internalSource.IsCancellationRequested
            End Get
        End Property


        Private ReadOnly tokens As CancellationToken()
        Private ReadOnly internalSource As CancellationTokenSource


        Private Sub New(internalSource As CancellationTokenSource, tokens As CancellationToken())
            Me.internalSource = internalSource
            Me.tokens = tokens
        End Sub


        Public Sub Cancel()
            Me.internalSource.Cancel()
        End Sub


        ''' 
        ''' Tries to unwrap  to any contained 
        '''  in this source. If token in exception is unknown,
        ''' nothing will be thrown and you have to elevate.
        ''' 
        ''' Caught exception which should be unwrapped.
        ''' Message which will be appended to the unwrapped exception.
        Public Sub ThrowIfCausedCancelOf(ex As OperationCanceledException, Optional message As String = Nothing)
            If ex.CancellationToken = Me.Token Then
                Me.ThrowIfAnyCancellationRequested(ex, message)
            End If
        End Sub


        ''' 
        ''' Throws  if any of contained tokens has had 
        ''' cancellation requested.
        ''' 
        Public Sub ThrowIfCancellationRequested()
            Me.ThrowIfCancellationRequested(Nothing, Nothing)
        End Sub


        ''' 
        ''' Throws  if any of contained tokens has had 
        ''' cancellation requested.
        ''' 
        Public Sub ThrowIfCancellationRequested(message As String)
            Me.ThrowIfCancellationRequested(Nothing, message)
        End Sub


        ''' 
        ''' Throws  if any of contained tokens has had 
        ''' cancellation requested.
        ''' 
        Public Sub ThrowIfCancellationRequested(ex As Exception, Optional message As String = Nothing)
            For i = 0 To Me.tokens.Length - 1
                If Me.tokens(i).IsCancellationRequested Then
                    Throw New OperationCanceledException(message, ex, Me.tokens(i))
                End If
            Next
        End Sub


        Public Shared Function Create(token1 As CancellationToken, token2 As CancellationToken) As LinkedCancellationTokenSource
            Dim internalSource = CancellationTokenSource.CreateLinkedTokenSource(token1, token2)
            Return New LinkedCancellationTokenSource(internalSource, {token1, token2})
        End Function


        Public Shared Function Create(ParamArray tokens As CancellationToken()) As LinkedCancellationTokenSource
            Dim internalSource = CancellationTokenSource.CreateLinkedTokenSource(tokens)
            Return New LinkedCancellationTokenSource(internalSource, tokens)
        End Function

#Region "IDisposable Support"
        Private disposedValue As Boolean ' To detect redundant calls

        ' IDisposable
        Protected Overridable Sub Dispose(disposing As Boolean)
            If Not Me.disposedValue Then
                If disposing Then
                    ' dispose managed state (managed objects).
                    Me.internalSource.Dispose()
                End If

                ' free unmanaged resources (unmanaged objects) and override Finalize() below.
                ' set large fields to null.
            End If
            Me.disposedValue = True
        End Sub

        ' override Finalize() only if Dispose(ByVal disposing As Boolean) above has code to free unmanaged resources.
        'Protected Overrides Sub Finalize()
        '    ' Do not change this code.  Put cleanup code in Dispose(ByVal disposing As Boolean) above.
        '    Dispose(False)
        '    MyBase.Finalize()
        'End Sub

        ' This code added by Visual Basic to correctly implement the disposable pattern.
        Public Sub Dispose() Implements IDisposable.Dispose
            ' Do not change this code.  Put cleanup code in Dispose(disposing As Boolean) above.
            Dispose(True)
            GC.SuppressFinalize(Me)
        End Sub

#End Region

    End Class

End Namespace

在上述示例中的用法：

Using linkedCts = LinkedCancellationTokenSource.Create(externalCancelToken, internalCancelToken)
    Try
        myRequest.Dispatch(linkedCts.Token)

    Catch ex As WebException When ex.Status = WebExceptionStatus.RequestCanceled
        linkedCts.ThrowIfCancellationRequested(ex)
        Throw

    Catch ex As OperationCanceledException
        linkedCts.ThrowIfCausedCancelOf(ex)
        Throw

    End Try
End Using

无论是好的还是不好的解决方案，请投票赞成/反对。 也欢迎更好地命名方法的想法。