multithreading problem - help!

[Andy Roxburgh]

Hi all,

I'm trying to program a multithreaded application - it currently
works, but I have two problems. I'm relatively new to VB.NET (C and
VB6 are my things) so I'm a bit lost here. The code is based on the
countdown / controlinvoker quickstart at GotDotNet.com.

The problems are:

(1) There's a memory leak somewhere. I don't know where, but it's
probably something stupid I've done when I added a second thread.

(2) How do I set it up to exit gracefully (i.e. where in the
application should I set threadsRunning = FALSE); at the moment even
when in debug mode it crashes when stopping - I assume because I
haven't sewn things up properly.

The basics of the thread architecture are below. I've added a second
thread to the quickstart code, and I've added a second ControlInvoker
instance. With regard to the two threads, one updates the screen and
the other communicates with a data comms interface, and passes some of
this data to the serial port. The communications routine should take
priority over the screen updating.

Can anyone cast an expert eye over it and tell me where I'm being
thick?

Thanks
Andy

=============== ============

' main application class:
Public Class Form1
Inherits System.Windows. Forms.Form
Private thrComms As Thread
Private thrDisplayUpdat e As Thread
Private threadsRunning As Boolean
Private controlInvoker As controlInvoker
Private controlInvoker2 As controlInvoker

' ...

Public Sub New()

MyBase.New()

Try
'This call is required by the Windows Form Designer.
InitializeCompo nent()
Catch ex As Exception
Stop
End Try
' InitialiseSeria lPort()

'Me.CreateGraph ics()
'Add any initialization after the InitializeCompo nent() call

Me.thrComms = New Thread(New ThreadStart(Add ressOf
Me.Thread_232))
Me.thrDisplayUp date = New Thread(New ThreadStart(Add ressOf
Me.Thread_Displ ayUpdate))

controlInvoker = New ControlInvoker( Me)
controlInvoker2 = New ControlInvoker( Me)

Me.thrComms.Pri ority = ThreadPriority. AboveNormal
Me.thrDisplayUp date.Priority = ThreadPriority. Normal

Me.thrComms.Sta rt()
Me.thrDisplayUp date.Start()

Me.threadsRunni ng = True
End Sub

'Form overrides dispose to clean up the component list.
Protected Overloads Overrides Sub Dispose(ByVal disposing As
Boolean)
MyBase.Dispose( disposing)
End Sub
' ....

Public Sub Thread_232()
' Data comms worker thread

Dim rxmsg_counter As Integer
Dim messages As sPCCanMsg

Dim temp_sec_value As Integer

controlInvoker = New ControlInvoker( Me)
'worker thread

Do
msg_list_size = 50
controlInvoker. Invoke(New MethodCallInvok er(AddressOf
interface_read_ Wrapper))
' get 50 messages
If (returned_statu s = HTX_SUCCESS) Then
' do processing
End If

'...
If cycle_count > 50 Then

' reset interface
'Thread.Sleep(1 )
controlInvoker. Invoke(New
MethodCallInvok er(AddressOf interface_stop_ Wrapper))

'Thread.Sleep(1 )
controlInvoker. Invoke(New
MethodCallInvok er(AddressOf interface_start _Wrapper))

cycle_count = 0
End If

Loop While Me.threadsRunni ng

End Sub
Public Sub Thread_display( )
controlInvoker2 = New ControlInvoker( Me)
Do
controlInvoker2 .Invoke(New MethodCallInvok er(AddressOf
update_display_ wrapper))
Loop While Me.threadRunnin g
End Sub
Private Sub update_display_ wrapper(ByVal arguments() As Object)
'----- Start the Display task
' Gets data from Global Variables, scales data and updates the screen.

' ......do lots of screen updating....

End Sub
Private Sub interface_start _wrapper(ByVal arguments() As Object)
canstatus2 = InterfaceStart( 1) ' DLL call to start the data comms
interface
End Sub
Private Sub interface_stop_ wrapper(ByVal arguments() As Object)
canstatus2 = InterfaceStop(1 )' DLL call to stop the data comms
interface
End Sub

Private Sub interface_read_ wrapper(ByVal arguments() As Object)
canstatus2 = InterfaceReadEx (1, msg_list(0), 5, 50)' DLL call to
read 50 messages from data comms interface
End Sub

End Class

=============== =============== =======

'''' CONTROLINVOKER CLASS ''''

Imports System
Imports System.Collecti ons
Imports System.Windows. Forms
Public Delegate Sub MethodCallInvok er(ByVal o() As Object)

' Control.Invoke allows a method to be invoked on the same thread as
the one
' the control was created on. Unlike in the full .NET Framework, the
..NET
' Compact Framework does not support the Control.Invoke overload for
passing an
' array of objects to pass as arguments. This ControlInvoker class
overcomes
' this limitation.
Public Class ControlInvoker

Private Class MethodCall
Public invoker As MethodCallInvok er
Public arguments() As Object
Public Sub New(ByVal invoker As MethodCallInvok er, ByVal
arguments() As Object)
Me.invoker = invoker
Me.arguments = arguments
End Sub 'New
End Class 'MethodCall

Private control As Control
Private argumentInvokeL ist As New Queue
' The constructor typically takes a form
Public Sub New(ByVal control As Control)
Me.control = control
End Sub 'New
' The delegate wrapping the method and its arguments
' to be called on the same thread as the control.
Public Sub Invoke(ByVal invoker As MethodCallInvok er, ByVal
ParamArray arguments() As Object)

Me.argumentInvo keList.Enqueue( New MethodCall(invo ker,
arguments))

control.Invoke( New EventHandler(Ad dressOf ControlInvoke))

End Sub 'Invoke
Private Sub ControlInvoke(B yVal sender As Object, ByVal e As
EventArgs)
Dim methodCall As MethodCall =
CType(argumentI nvokeList.Deque ue(), MethodCall)
Try
methodCall.invo ker(methodCall. arguments)
Catch ex As Exception
Debug.Assert(Fa lse)

End Try

End Sub 'ControlInvoke
End Class 'ControlInvoker