SQLException when Canceling Async Query

Question

Using the new .Net 4.5 Async/Await functionality with a CancellationToken, I get a SQLException when I cancel a ExecuteNonQueryAsync call, instead of a OperationCanceledException (or some other exception that is specific to canceling an operation). The SQLException does say Operation cancelled by user at the end of the message. I expected a more specific exception to be thrown when canceling the operation. Additionally, how would I create the appropriate Try/Catch handlers to deal with this expected scenario? I normally would have the SQLException as more general failure block, but now I would have to tease out the text of the message to see if this just the user clicking the Cancel button!? I must be missing something.

Here's a simple VB WinForm app that has two buttons, one to do the Async call, and the other to cancel. The Try/Catch in the 1st button shows the SQLException that is hit when the 2nd button calls the Cancel method.

Dim _cts As CancellationTokenSource
Private Async Sub btnLocalTest_Click(sender As Object, e As EventArgs) Handles btnLocalTest.Click
    _cts = New CancellationTokenSource()
    Dim CancelToken As CancellationToken = _cts.Token
    Using sconn As New SqlConnection("server=(local);database=MyDB;user id=MyUser;password=MyPassword")
        sconn.Open()
        Dim SQL As String = some long running SELECT or INSERT statement
        Try
            Using scmd As New SqlCommand(SQL, sconn)
                scmd.CommandTimeout = 300
                Dim i As Integer = Await scmd.ExecuteNonQueryAsync(CancelToken)
            End Using
        Catch exCancel As OperationCanceledException
            LogEvent("Query canceled Exception.") ' This error is *not* thrown on Cancel.  
        Catch ex As SqlClient.SqlException
            LogEvent("Error with query. " & ex.Message)  ' This error *is* thrown on Cancel.  Message includes text 'Canceled by user.'
        End Try
        sconn.Close()
        _cts = Nothing
    End Using
End Sub

Private Sub btnLocalTestCancel_Click(sender As Object, e As EventArgs) Handles btnLocalTestCancel.Click
    If _cts IsNot Nothing Then
        _cts.Cancel()
    End If
End Sub

UPDATE: I created a different Async test with the HttpClient.GetAsync method that supports cancellation. When you cancel that task, you can the OperationCanceledException exception that I originally expected above. So the question remains: what exception should you get when you cancel an Async task? Or is that dependent upon each method and it's implementation?

Answer 1

I "solved" this issue by checking CancelToken.IsCancellationRequested in the Catch ex As SqlClient.SqlException block.