Vb.Net - Invoke in Task - vb.net

Question

so basically I want my application to run a method that is quite cpu intensive and therewhile it should constantly display status information on a different form. To prevent this status form from freezing, I thought it would be a good idea to outsource the code into a new thread.
First I tried to use basic threadding and invoking the richtextbox control which should display status messages. - Problem is - I need to know when the Thread is finished to carry on with my main thread. Obviously I cannot simply run a loop in my main thread that keeps checking if the process is finished, cause that would make my GUI freeze, too.
So I did a little bit research and found out about Tasks.
That's how it looks:
Dim z as new complexProcessClass
Dim taskA = task.Factory.StartNew(Sub() z.start())
taskA.Wait()
If taskA.IsCompleted Then
MsgBox("finished")
End If
And whenever the process reports a status I use this:
Public Class complexProcessClass
dim statusWindow as statusForm
Public Sub start()
statusWindow = new statusForm
'complex code here
reportStatus("bla")
'complex code here
reportStatus("blabla")
'complex code here
End Sub
Private Delegate Sub UpdateTextHandler(ByVal Text As String)
Private Sub reportStatus(Byval s as String)
If z.RichTextBox1.InvokeRequired Then
Try
z.RichTextBox1.Invoke(New UpdateTextHandler(AddressOf xform.RichTextBox1.AppendText), s)
Catch ex As Exception
MsgBox(ex.ToString())
End Try
Else
z.RichTextBox1.AppendText(s)
End If
End Sub
But it just keeps freezing on the invoke call - no error message - nothing?!
Can anybody tell me the correct way to do this? - and please no backgroundworker solution ;)
thanks in advance

Answer 1

Take a look at the BackgroundWorker class. This post should get you started.
Another approach is to create delegates and call the thread asynchronously and implement an update function to catch when the work is done.
Create a class with the work code as a function
At the top of the class create/add Delegate Function Handler
Inside of your form add a handler to the new class with a call to your class method.
Create a callbackhandler method to receive the status of the thread performing the export functionality.Have the callbackhandler call an update ui function that checks if the thread is running from the UI or is another thread. (Me.InvokeRequired checks this)
Inside of the Form btn click event call the method using
the targetHandler call.
The below code is what the form code would look like.
Public Class Form1
Private targetHandler As ClassName.Handler = AddressOf objNewClass.somework
Private callbackHandler As AsyncCallback _
= AddressOf MyCallbackMethod
Sub MyCallbackMethod(ByVal ar As IAsyncResult)
'*** this code fires at completion of each asynchronous method call
Try
Dim retval As Boolean = targetHandler.EndInvoke(ar)
If retval = True Then
Console.Write(retval)
End If
UpdateUI("Task complete")
Catch ex As Exception
Dim msg As String
msg = "Error: " & ex.Message
UpdateUI(msg)
End Try
End Sub
Sub UpdateUI(ByVal statusMessage As String)
If Me.InvokeRequired Then
Dim handler As New UpdateUIHandler(AddressOf UpdateUI_Impl)
Dim args() As Object = {statusMessage}
Me.BeginInvoke(handler, args)
Else
UpdateUI_Impl(statusMessage)
End If
End Sub
Delegate Sub UpdateUIHandler(ByVal statusMessage As String)
Sub UpdateUI_Impl(ByVal statusMessage As String)
Me.sbMain.Panels("Status").Text = statusMessage
End Sub
'Call to your worker thread
Private Sub btn_Click() Handles Button1.Click
Dim result As IAsyncResult =targetHandler.BeginInvoke(callbackHandler,Nothing)
End Sub
End Class

Answer 2

You have a deadlock situation where taskA.Wait() is blocking the UI thread, and the Invoke() call inside taskA is waiting for the UI thread to finish what it's doing. Which is waiting until it's done waiting. Which is never.
I'm not entirely sure, but try this:
Dim taskA = task.Factory.StartNew(Sub() z.start()).ConfigureAwait(False)