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Thread.Join Deadlock with Invoke

September 7, 2007

If you are trying to Make Thread-Safe Calls to Windows Forms Controls then you can run into deadlock problems when calling ‘Invoke’ from your thread, if your main thread is waiting for a Thread.Join on the calling thread.

I posted a workaround for this on the Microsoft site, which uses an extra thread to make the call to Invoke method, to avoid the deadlock.

VB.NET example:

Private Sub SetText(ByVal str_text As String)
        If Me.textbox1.InvokeRequired = True Then
                'call an asyncronous invoke, by calling it then forcing a DoEvents
                Dim asyncInvokeThread As New Threading.Thread(New Threading.ParameterizedThreadStart(AddressOf AsyncInvoke))
                asyncInvokeThread.IsBackground = True
                asyncInvokeThread.Start(str_text)
 
                Application.DoEvents()
        Else
                me.textbox1.text=str_text
        End If
End Sub
Private Sub AsyncInvoke(ByVal obj_text As Object)
        Dim str_text As String = CStr(obj_text)
        Dim d As New SetTextCallback(AddressOf SetText)
        Me.Invoke(d, New Object() {str_message})
End Sub

Posted in .NET, Threading, VB.NET — 2 Comments

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2 Comments to “Thread.Join Deadlock with Invoke”

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craig w

January 6, 2011 at 10:00 am | Permalink

Hi, this particular problem would be the cause if your main thread (UI) has code which is blocking at Thread.Join() to the thread on which the call to Invoke() is made. If your main thread is waiting on the worker thread but the worker is trying to Invoke something on the main thread, then you get the race condition described in the article.

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Bart

January 6, 2011 at 8:13 am | Permalink

Hi,

I know this is an old article (http://www.craigwardman.com/blog/index.php/2007/09/thread-join-deadlock-with-invoke/)

However I am in a situation that looks very similar. I have an PDA application with weird hangups that I can’t trace back to any part of the code. I do use invokerequired.

I just ported the PDA application (.NETCF) to .NET and found this morning I have a similar looking hangup. With Spy++ I found that I am in a race condition with WM_PAINT messages, and acutally I only use invokerequired with the refresh method on the UI thread.

As sample (a timer callback in the UI)

Private Sub onChangingTimerTimeout(ByVal state As Object)
changingSystem = False
Try
If Me.InvokeRequired Then
Me.Invoke(refreshDelegate)
Else
Me.Refresh()
End If
Catch ex As Exception
End Try
End Sub

the refreshDelegate is a simple method calling me.refresh().

I would appreciate very much if you could let me know if the code as I wrote here is exposing me to this deadlock situation.

Kind regards

Bart

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