Proper way to terminate thread

Question

Hello

I use Thread to run a heavy code in non-UI mode:

Define it to be accessible in the whole form:

Private MyThread As Thread

Under Cancel Button:

If MyThread IsNot Nothing Then MyThread.Abort()

And starting thread:

MyThread = New Thread(New ThreadStart(AddressOf ThreadRoute))

MyThread.Start()

The problem?

5 System.Threading.ThreadAbortExceptions and this error:

An exception of type 'System.Threading.ThreadAbortException' occurred in blah.exe but was not handled in user code

Where and how should I handle cancellation?

Thanks :)

Answer 1

Hi,@Peter Volz. Welcome to Microsoft Q&A Forum.

To handle cancellation more effectively, you could use the CancellationToken and CancellationTokenSource classes, which provide a cooperative cancellation mechanism.

Here's an example of how you can use the CancellationTokenSource and CancellationToken for cooperative cancellation:

Imports System.Threading

Class MainWindow

    Private cancellationTokenSource As CancellationTokenSource

    Private Sub CancelButton_Click(sender As Object, e As EventArgs)
        If cancellationTokenSource IsNot Nothing Then
            cancellationTokenSource.Cancel()
        End If
    End Sub

    Private Sub ThreadRoute()
        Dim token As CancellationToken = cancellationTokenSource.Token

        ' For example:
        While True
            If token.IsCancellationRequested Then
                ' Clean up or save the current state before exiting
                Exit While
            End If
            ' Perform heavy work here
        End While
    End Sub

    Private Sub StartThread()
        cancellationTokenSource = New CancellationTokenSource()

        Dim thread As New Thread(AddressOf ThreadRoute)
        thread.Start()
    End Sub


End Class

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Answer 2

Have you seen these -

https://learn.microsoft.com/en-us/dotnet/standard/threading/cancellation-in-managed-threads

https://learn.microsoft.com/en-us/dotnet/standard/threading/using-threads-and-threading#how-to-stop-a-thread

Answer 3

Thread abort is typically not the way to do this, though there are exceptions.

Here is the proper way.

https://learn.microsoft.com/en-us/dotnet/standard/threading/cancellation-in-managed-threads

Answer 4

Some older programs may have dangerous usage like this. When aborting, also check the IsAlive property, execute the Abort method, execute the Join method, and wait until it finishes.

If MyThread IsNot Nothing Then
    If MyThread.IsAlive Then
        MyThread.Abort()
    End If
    MyThread.Join()
End If

Note that this is not a good implementation.