[Barret]

At some point in time, if it didn't happen already, when you create forms and threads and it happens to be
you close the form without closing the thread, any calls from within that thread that is making changes
to let say, a textbox or some concept of a log view, it will flip you off with an exception.

Example exception
https://msdn.microsoft.com/en-us/library....110).aspx

Controls and forms have properties such as "IsDisposed" and "IsAccessible" but neither of those do fuck all.

What we need is a proper locking mechanism that locks and block calls of such disposed controls.
I saw a few methods, some even very elaborate using the OnClose procedures but yet they do not do want i want.
This might be an solution yet i did not fully test it but seems to work.

Quick setup:

Add the following to your form class

PHP Code


<?php 
Private Property ExitLock As Object
Private Property ExitFlag As Boolean 


And initialize them on OnFormLoad event

PHP Code


<?php 
Me.ExitFlag = False
Me.ExitLock = New Object 


And we add this to the OnFormClosing event

PHP Code


<?php 
Me.FlagForShutdown() 


Add this subroutine, this will be our enabler when we are closing so both parties are knowing "whats going on"

PHP Code


<?php 
Private Sub FlagForShutdown()
        SyncLock Me.ExitLock
            Me.ExitFlag = True
        End SyncLock
End Sub 


And in your thread worker, you make the following construction.
(Assuming you have setup a loop where a boolean determines the status of that loop)

PHP Code


<?php 
Private Sub FlagForShutdown()
 Synclock Me.ExitLock
   Do
            .......thread worker code....
            If (Me.ExitFlag) Then
               ...perform safe and clean exit code....
            End If
  While Bool
 End Synclock
End Sub 


And for the procedures that interact between the thread and form, you add the following.
(This is just an example of a output logger for some debug info coming from another thread)

PHP Code


<?php 
Private Sub DebugLog(Message As String, Optional Clear As Boolean = False)
 If (Not Me.ExitFlag) Then
        If (Me.InvokeRequired) Then
            Me.Invoke(Sub() Me.DebugLog(Message, Clear))
        Else
            If (Clear) Then Me.Textbox.Clear()
            Me.Textbox.AppendText(String.Format("{0}{1}", Message, Environment.NewLine))
            Me.Textbox.SelectionLength = Me.Textbox.Text.Length
            Me.Textbox.ScrollToCaret()
        End If
 End If
End Sub 


This will, in my idea, avoid having these exceptions. But i'm not entirely sure if this would be the best, so i'll leave this here and see who is going to add his post.

Ps. Yes i know of 'ManualResetEvent' but thats not what im asking here.


- B.

[hfTP54]

Wow man thanks so much I needed this as all my new themes rely on a global timer which can dispose objects so closing forms becomes a mess coz of this error. I'm surprised that no one else got this.

[Rhez]

Never encounter those error when working on thread. Maybe I can use this in the future.
Thanks Barret. 🤝

[Barret]

Never encounter those error when working on thread. Maybe I can use this in the future.
Thanks Barret. 🤝

Depends how you work your threads, if you have threads send off that do stuff and report back, while you happen to close the form itself, you will encounter this error "Trying to access a disposed control". So in order to prevent it, you must have a gate keeper that tells the callback to halt and return earlier without doing the reporting and die off.