Async/Await questions

Question

I'm using webforms and VB.net. I am calling Stripe to perform an ACH transaction. I have a standalone program that works, however when I put the code in my production application, the flow is not what I'm expecting.

I'm reading a gridview which contains customer IDs of records which need to be billed via Stripe. I have a button (btnPost) which starts the process. That button calls an Async Sub which loops through the gridview. For each row I call a "Post_ACHAsync" subroutine, which is also Async. Within the "Post_ACHAsync" subroutine is the call to Stripe, with an "Await", which returns a Task.

The problem is that, when the call to Stripe is done, it goes back to the For/Each loop instead of proceeding with code. Why is it doing that?

Here's the code:


Protected Sub btnPost_Click(sender As Object, e As EventArgs) Handles btnPost.Click

    PostTransactions()
    PopulatePendingTrxs()

End Sub


    Protected Async Sub PostTransactions()
        For Each row As GridViewRow In gvTrxs.Rows
            Select Case row.Cells(2).Text.ToUpper()
                Case "B"
                    '--- Bank Account (ACH)
                    Post_ACHAsync([parameters])
                Case "C"
                    '--- Credit Card
                    Post_CC(row)
                Case Else

            End Select
        Next
    End Sub


  Private Async Sub Post_ACHAsync([parameters])          
    dim oM as new BillingMaster()
    
      '--- call Stripe
          Try
              Dim stripeService As New StripeService()
              Dim chargeId As String = Await stripeService.ProcessAchTransferAsync([parameters])
              ' Success!
              oM.Status = "W"     'Withdrawal
              oM.SuccessOrFailure = "S"
              oM.StripeWithdrawalID = chargeId
              oM.StripeWithdrawalMsg = "Success"
              colErrors = oM.SaveRecord(oM)
          Catch ex As Exception
              OKtoContinue = False
              colErrors.Add(ex.Message)
          End Try

      If Not OKtoContinue Then
          oM.PostGUID = strPostGUID
          oM.Status = "F"
          oM.SuccessOrFailure = "F"
          oM.StripeWithdrawalID = ""
          oM.WithdrawalDate = DateTime.Now
          oM.StripeWithdrawalMsg = SplitErrors(colErrors)
          colErrors = oM.SaveRecord(oM)
      End If

      oM = Nothing

  End Sub   
  
  
  Public Async Function ProcessAchTransferAsync([parameters]) As Task(Of String)
    Try
        
        '--- do Stripe stuff here

        Return charge.Id
        
    Catch ex As StripeException
        ' Log the error
        System.Diagnostics.Debug.WriteLine($"Stripe Error: {If(ex.StripeError?.Message, ex.Message)}")
        Throw New Exception($"Payment processing error: {If(ex.StripeError?.Message, ex.Message)}")
        
    Catch ex As Exception
        ' Log the error
        System.Diagnostics.Debug.WriteLine($"General Error: {ex.Message}")
        Throw New Exception("An unexpected error occurred while processing your payment. Please try again.")
        
    End Try
    
End Function

After the Await stripeService.ProcessAchTransferAsync line, the flow goes back to the For/Each loop; it doesn't continue with the "Success" (or Catch) code.

Do I need both subroutines to be Async? Should there be another "Await" somewhere?

btnPost_Click needs to be marked async, then await the methods there; it's OK for event handlers to be async void (it's handled internally). The other methods not so much. Change them from async void to async Task. Await the async calls — Jimi
– Jimi, Commented Mar 30 at 18:33
Remember that when you use Async, it's Async all the way down. Every step in the chain needs to go through an Await. — Craig
– Craig, Commented Mar 31 at 15:05
You really shouldn't use a UI control to store data - instead, store the data somewhere else, for example a DataTable, and display that data with a UI control, for example with the GridView.DataBind Method. Trying to use a UI control for processing data will result in slower processing. — Andrew Morton
– Andrew Morton, Commented Mar 31 at 18:57

Étienne Laneville · Accepted Answer · 2025-04-07 20:56:51Z

Because Post_ACHAsync is not awaited, the execution flow immediately returns to PostTransactions when the Await line is reached:

Dim chargeId As String = Await stripeService.ProcessAchTransferAsync([parameters])

Take a look at the diagram in the Task asynchronous programming model article:

The same is happening with your code where control is returned to the calling method when the Await statement is reached.

You should await the Post_ACHAsync call:

Protected Async Sub PostTransactions()
    For Each row As GridViewRow In gvTrxs.Rows
        Select Case row.Cells(2).Text.ToUpper()
            Case "B"
                '--- Bank Account (ACH)
                Await Post_ACHAsync([parameters])
            Case "C"
                '--- Credit Card
                Await Post_CC(row)
        End Select
    Next
End Sub

You should also Await PostTransactions in your button event handler:

Protected Async Sub btnPost_Click(sender As Object, e As EventArgs) Handles btnPost.Click

    Await PostTransactions()
    PopulatePendingTrxs()

End Sub

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