Handler Stack Overflow?!?!

[tomb]

Please help!

I have a handler in a class that handles when a column in a table is
modified, as such:

dtWhatif = dsOp.Tables("whatif")
AddHandler dtWhatif.ColumnChanged, New
DataColumnChangeEventHandler(AddressOf Whatif_Changed)

When testing this, I got an error: An unhandled exception of type
'System.StackOverflowException' occurred in system.dll

So I put a debug statement in to see why the stack is overflowing. This
handler was called 4082 times! All I did was change the value in one
cell of a datagrid!

Why?! Why?!

Tom

[Chris Dunaway]

> dtWhatif = dsOp.Tables("whatif")

AddHandler dtWhatif.ColumnChanged, New
DataColumnChangeEventHandler(AddressOf Whatif_Changed)

What happens in Whatif_Changed?

[tomb]

Right now, it just calls and empty function. I was just testing the
handler, and found it doesn't work as expected.

Tom

Chris Dunaway wrote:

dtWhatif = dsOp.Tables("whatif")
AddHandler dtWhatif.ColumnChanged, New
DataColumnChangeEventHandler(AddressOf Whatif_Changed)

What happens in Whatif_Changed?

[tomb]

I just tried commenting out the call to the other function from within
the event handler. Guess what? No problem. I only get the stack
overload if the handler calls another function. This is not a good
thing, because I need to be able to call several functions when the
column has changed. Any suggestions?

Tom

Chris Dunaway wrote:

dtWhatif = dsOp.Tables("whatif")
AddHandler dtWhatif.ColumnChanged, New
DataColumnChangeEventHandler(AddressOf Whatif_Changed)

What happens in Whatif_Changed?

[Bob Powell [MVP]]

What Chris meant was please post your code. You have obviously generated some race condition here.

--
Bob Powell [MVP]
Visual C#, System.Drawing

Ramuseco Limited .NET consulting
http://www.ramuseco.com

Find great Windows Forms articles in Windows Forms Tips and Tricks
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"tomb" <to**@technetcenter.com> wrote in message news:6b*****************@bignews3.bellsouth.net...
I just tried commenting out the call to the other function from within the event handler. Guess what? No problem. I only get the stack overload if the handler calls another function. This is not a good thing, because I need to be able to call several functions when the column has changed. Any suggestions?

Tom

Chris Dunaway wrote:

dtWhatif = dsOp.Tables("whatif")
AddHandler dtWhatif.ColumnChanged, New
DataColumnChangeEventHandler(AddressOf Whatif_Changed)


What happens in Whatif_Changed?

[tomb]

Ok, here's the code:
Private Sub Whatif_Changed(ByVal sender As Object, ByVal e As
DataColumnChangeEventArgs)
Static i As Integer = 0
'I added i for the debugger
i += 1

Debug.WriteLine("This is cycle number " & i)
calcWhatif(e.Column.ColumnName, e.Row.Item(0))
'if calcWhatif is commented out, then this handler is called once,
otherwise it just keeps being called and the next
debug line never fires - the call stack overloads first.

Debug.WriteLine("Column " & e.Column.Ordinal)

End Sub

Right now, calcWhatif doesn't do anything. The code that was going to
be there can go in the handler, but I still will need to call other
functions as part of that calculation.

Thanks for any clarification you can provide.

Tom

Bob Powell [MVP] wrote:

What Chris meant was please post your code. You have obviously
generated some race condition here.

--
Bob Powell [MVP]
Visual C#, System.Drawing

Ramuseco Limited .NET consulting
http://www.ramuseco.com

Find great Windows Forms articles in Windows Forms Tips and Tricks
http://www.bobpowell.net/tipstricks.htm

Answer those GDI+ questions with the GDI+ FAQ
http://www.bobpowell.net/faqmain.htm

All new articles provide code in C# and VB.NET.
Subscribe to the RSS feeds provided and never miss a new article.


"tomb" <to**@technetcenter.com <mailto:to**@technetcenter.com>>
wrote in message news:6b*****************@bignews3.bellsouth.net...
I just tried commenting out the call to the other function from
within the event handler. Guess what? No problem. I only get
the stack overload if the handler calls another function. This is
not a good thing, because I need to be able to call several
functions when the column has changed. Any suggestions?

Tom

Chris Dunaway wrote:

dtWhatif = dsOp.Tables("whatif")
AddHandler dtWhatif.ColumnChanged, New
DataColumnChangeEventHandler(AddressOf Whatif_Changed)

What happens in Whatif_Changed?

[Chris Dunaway]

tomb wrote:

calcWhatif(e.Column.ColumnName, e.Row.Item(0))
Debug.WriteLine("Column " & e.Column.Ordinal)

Right now, calcWhatif doesn't do anything. The code that was going to

Does calcWhatif have any code in it at all? The behavior you are
describing sounds like the calcWhatif method is changing the column
which in turn causes the column changed event to fire which executes
calcWhatif which changes the column which in turn causes the column
changed event to fire and on and on until the stack over flows.

What you can try is declaring a boolean property outside the method,
for example called bColumnChanging. Then, inside the event, you check
that boolean:

If Not bColumnChanging Then
bColumnChanging = True

'...rest of code here

bColumnChanging = False
End If

But first you should determine exactly why the stack is overflowing.

[Bob Powell [MVP]]

This wouldn't cause a stack overflow. Just the efficient eating up of 100%
of the processor. It sounds to me as if CalcWhatIf calls CalcWhatIf
internally and is causing a recursive problem.

If however the OP refuses to post the actual code instead of being all coy
about the content of his method then there's not a whole lot we can do ;-)

--
Bob Powell [MVP]
Visual C#, System.Drawing

Ramuseco Limited .NET consulting
http://www.ramuseco.com

Find great Windows Forms articles in Windows Forms Tips and Tricks
http://www.bobpowell.net/tipstricks.htm

Answer those GDI+ questions with the GDI+ FAQ
http://www.bobpowell.net/faqmain.htm

All new articles provide code in C# and VB.NET.
Subscribe to the RSS feeds provided and never miss a new article.

"Chris Dunaway" <du******@gmail.com> wrote in message
news:11**********************@g44g2000cwa.googlegr oups.com...

tomb wrote:

calcWhatif(e.Column.ColumnName, e.Row.Item(0))
Debug.WriteLine("Column " & e.Column.Ordinal)

Right now, calcWhatif doesn't do anything. The code that was going to

Does calcWhatif have any code in it at all? The behavior you are
describing sounds like the calcWhatif method is changing the column
which in turn causes the column changed event to fire which executes
calcWhatif which changes the column which in turn causes the column
changed event to fire and on and on until the stack over flows.

What you can try is declaring a boolean property outside the method,
for example called bColumnChanging. Then, inside the event, you check
that boolean:

If Not bColumnChanging Then
bColumnChanging = True

'...rest of code here

bColumnChanging = False
End If

But first you should determine exactly why the stack is overflowing.

[tomb]

I told you already, calcWhatif doesn't do anything yet. I haven't put
any code in it other than this:

Private Sub calcWhatif(ByRef sColumn As String, ByRef iRow As String)

Dim dr As DataRow
Dim drW As DataRow
Dim ProdPos As ProductPosition 'a small defined class object

Static i As Integer = 0

i += 1

Debug.WriteLine("calcWhatif " & i)

End Sub

I added the debug piece to help me see what was going on.

The handler is as follows:

Private Sub Whatif_Changed(ByVal sender As Object, ByVal e As
DataColumnChangeEventArgs)

Static i As Integer = 0

i += 1

Debug.WriteLine("This is cycle number " & i)

calcWhatif(e.Column.ColumnName, e.Row.Item(0))
Debug.WriteLine("Column " & e.Column.Ordinal)

End Sub

So, right now the handler is calling an empty function that just returns
after outputting the debug info. The problem is that the handler is
being called again before returniing from calcWhatif to run the second
debug line. I never get to see the column ordinal displayed.

But if I take out the call to calcWhatif, everything is fine - I see the
ordinal value and the handler runs once. This handler has to be able to
call another function, because I have to run calculations based on the
changed value.

Any insight?

Tom
Bob Powell [MVP] wrote:

This wouldn't cause a stack overflow. Just the efficient eating up of 100%
of the processor. It sounds to me as if CalcWhatIf calls CalcWhatIf
internally and is causing a recursive problem.

If however the OP refuses to post the actual code instead of being all coy
about the content of his method then there's not a whole lot we can do ;-)

[tomb]

Would you believe it, when I changed the parameters to being passed
byVal, everything was fine. Something to take note of for event
handlers - calling another function ByRef explodes!

Tom

Bob Powell [MVP] wrote:

This wouldn't cause a stack overflow. Just the efficient eating up of 100%
of the processor. It sounds to me as if CalcWhatIf calls CalcWhatIf
internally and is causing a recursive problem.

If however the OP refuses to post the actual code instead of being all coy
about the content of his method then there's not a whole lot we can do ;-)

[Jay B. Harlow [MVP - Outlook]]

Tomb,
You also need to be very careful which changing a the value of a column on a
row, in the ColumnChanged event handler, as this will cause the event to be
raised, which will cause the handler to be called, causing the row to be
changed causing the event to be raised, causing the handler to be called,
causing the row to be changed, causing the event to be raised, causing ...
.... causing Stack Overflow...

I normally put a "guard" condition in my handler to exit the handler if a
column I am not interested (such as the column I am about to change) has
changed... Alternatively I will check to see if only the columns I am
interested in have changed, such as the columns that are input into a
formula I am calculating in the ColumnChanged event...

Hope this helps
Jay

"tomb" <to**@technetcenter.com> wrote in message
news:JP******************@bignews5.bellsouth.net.. .
| Would you believe it, when I changed the parameters to being passed
| byVal, everything was fine. Something to take note of for event
| handlers - calling another function ByRef explodes!
|
| Tom
|
| Bob Powell [MVP] wrote:
|
| >This wouldn't cause a stack overflow. Just the efficient eating up of
100%
| >of the processor. It sounds to me as if CalcWhatIf calls CalcWhatIf
| >internally and is causing a recursive problem.
| >
| >If however the OP refuses to post the actual code instead of being all
coy
| >about the content of his method then there's not a whole lot we can do
;-)
| >
| >
| >