MessageBox.Show hangs execution

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Guest

I have an MDI parent with one or more children forms. Each child form has an engine thread that processes data. The child form's _Closing event is roughly

01 Private Sub frmConvertable_Closing(sender, e
02 'Show the form (other MDI children may be on top
03 Me.Activate(
04 mvarEngineThread.Suspen
05 e.Cancel = MessageBox.Show(strQuitMessage, strQuitTitle,
MessageboxButtons.OKCancel) = DialogResult.Cance
06 mvarEngineThread.Resum
07 'Thread is terminated in _Closed even
08 End Su

When I run the application and hold down Esc to continually call the closing event and cancel the messagebox (resume processing), after a few seconds the application hangs. Breaking into the debugger shows that line 05 is highlighted green

If I comment out the mvarEngineThread suspend and resume (lines 04 and 06) the application never hangs when I hold down Esc

Can anybody offer an explaination for this?
 
Pi said:
I have an MDI parent with one or more children forms. Each child
form has an engine thread that processes data. The child form's
_Closing event is roughly:

01 Private Sub frmConvertable_Closing(sender, e)
02 'Show the form (other MDI children may be on top)
03 Me.Activate()
04 mvarEngineThread.Suspend
05 e.Cancel = MessageBox.Show(strQuitMessage, strQuitTitle, _
MessageboxButtons.OKCancel) =
DialogResult.Cancel
06 mvarEngineThread.Resume
07 'Thread is terminated in _Closed event
08 End Sub

When I run the application and hold down Esc to continually call the
closing event and cancel the messagebox (resume processing), after a
few seconds the application hangs. Breaking into the debugger shows
that line 05 is highlighted green.

If I comment out the mvarEngineThread suspend and resume (lines 04
and 06) the application never hangs when I hold down Esc.

Can anybody offer an explaination for this?
Click to expand...

Did you set the cancelbutton property of the MDI child to close the child
using ESC? That's what I assumed to test the situation. I could not
reproduce the problem (VB 2003). I held down ESC several seconds.

This is my code in the child window:

Dim t As Threading.Thread

Private Sub Button1_Click( _
ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button1.Click

t = New Threading.Thread(AddressOf threadstart)
t.Start()
End Sub

Private Sub threadstart()
Do
Threading.Thread.Sleep(100)
Loop
End Sub

Private Sub Form2_Closing( _
ByVal sender As Object, _
ByVal e As System.ComponentModel.CancelEventArgs) _
Handles MyBase.Closing

2: 'Show the form (other MDI children may be on top)
3: Me.Activate()
4: t.Suspend()
5: e.Cancel = MessageBox.Show("", "", _
MessageBoxButtons.OKCancel) = DialogResult.Cancel
6: t.Resume()
7: 'Thread is terminated in _Closed event

End Sub

Private Sub Form2_Closed( _
ByVal sender As Object, ByVal e As System.EventArgs) _
Handles MyBase.Closed

t.Abort()
End Sub

Private Sub Button2_Click( _
ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button2.Click

Me.Close()
End Sub


After opening the child, I clicked button1 to start the thread, then held
down Esc.
 
Armin,

Your code looks very similiar to my test code (VB 2003). The only difference I can see is the threading procedure:

Public Sub ThreadProc()
Do
For i As Integer = 0 To 1000
Dim a As New System.Text.StringBuilder(400)
Next
System.Threading.Thread.Sleep(0)
Loop
End Sub

----- Armin Zingler wrote: -----

Pi said:
I have an MDI parent with one or more children forms. Each child
form has an engine thread that processes data. The child form's
_Closing event is roughly:
02 'Show the form (other MDI children may be on top)
03 Me.Activate()
04 mvarEngineThread.Suspend
05 e.Cancel = MessageBox.Show(strQuitMessage, strQuitTitle, _
MessageboxButtons.OKCancel) =
DialogResult.Cancel
06 mvarEngineThread.Resume
07 'Thread is terminated in _Closed event
08 End Sub
closing event and cancel the messagebox (resume processing), after a
few seconds the application hangs. Breaking into the debugger shows
that line 05 is highlighted green.
and 06) the application never hangs when I hold down Esc.
Click to expand...

Did you set the cancelbutton property of the MDI child to close the child
using ESC? That's what I assumed to test the situation. I could not
reproduce the problem (VB 2003). I held down ESC several seconds.

This is my code in the child window:

Dim t As Threading.Thread

Private Sub Button1_Click( _
ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button1.Click

t = New Threading.Thread(AddressOf threadstart)
t.Start()
End Sub

Private Sub threadstart()
Do
Threading.Thread.Sleep(100)
Loop
End Sub

Private Sub Form2_Closing( _
ByVal sender As Object, _
ByVal e As System.ComponentModel.CancelEventArgs) _
Handles MyBase.Closing

2: 'Show the form (other MDI children may be on top)
3: Me.Activate()
4: t.Suspend()
5: e.Cancel = MessageBox.Show("", "", _
MessageBoxButtons.OKCancel) = DialogResult.Cancel
6: t.Resume()
7: 'Thread is terminated in _Closed event

End Sub

Private Sub Form2_Closed( _
ByVal sender As Object, ByVal e As System.EventArgs) _
Handles MyBase.Closed

t.Abort()
End Sub

Private Sub Button2_Click( _
ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button2.Click

Me.Close()
End Sub


After opening the child, I clicked button1 to start the thread, then held
down Esc.
 
Pi said:
Your code looks very similiar to my test code (VB 2003). The only
difference I can see is the threading procedure:

Public Sub ThreadProc()
Do
For i As Integer = 0 To 1000
Dim a As New System.Text.StringBuilder(400)
Next
System.Threading.Thread.Sleep(0)
Loop
End Sub
Click to expand...


With this code I can reproduce the problem! I'm gonna have a look at it.
 
Pi said:
Thanks for that Armin. Can you let me know if you find
anything?
Click to expand...


First I thought it might be a garbage collection issue because constantly
creating new stringbuilders should make the GC work heavily. On the other
side, there is no CPU usage when the app is locked. Then I had a look at the
callstack, the threads, the disassembly and the IL code - but I don't know
much more now, I mean, I didn't find the problem.

I tried this:
Dim a As New System.Text.StringBuilder(400)
a = Nothing
GC.Collect()

Now the app isn't locked anymore. Without it, I think there must be a kind
of dead-lock anywhere. Anybody else's got an explanation?
 
First I thought it might be a garbage collection issue because constantly
creating new stringbuilders should make the GC work heavily. On the other
side, there is no CPU usage when the app is locked. Then I had a look at the
callstack, the threads, the disassembly and the IL code - but I don't know
much more now, I mean, I didn't find the problem.

I tried this:
Dim a As New System.Text.StringBuilder(400)
a = Nothing
GC.Collect()

Now the app isn't locked anymore. Without it, I think there must be a kind
of dead-lock anywhere. Anybody else's got an explanation?


--
Armin

http://www.plig.net/nnq/nquote.html
http://www.netmeister.org/news/learn2quote.html


I tried your code:

Dim a As New System.Text.StringBuilder(400)
a = Nothing
GC.Collect()

After holding down Esc for over 15 secs the app then hung itself. I'm baffled with this one.
 
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