StackOverflowException without recursion or infinite loop?

Question

Background

I have a DataGridView control which I am using, and I added my handler below to the DataGridView.CellFormatting event so the values in some cells can be made more human-readable. This event handler has been working great, formatting all values without issue.

Recently however, I have discovered a very rare circumstance causes an unusual bug. The column in my DataGridView for the item's due date always has an int value. 0 indicates the event is never due, any other value is a UTC timestamp for the due date. The MySQL db column corresponding doesn't allow nulls. When the user has moved from one DataGridView row with a due date, to another DataGridView row with a due date (at this point everything is still appears fine), and then presses a button which reloads the data from the database (without sending updates, essentially calling DataAdapter.Fill()), the program generates a StackOverflowException**.

No recursion?

What is so unusual to me is that I do not see where the recursion or infinte-looping is. I added int cellFormatCallCount as a class member, and increment it during each call, but at the time the exception is thrown, the debugger shows the value of that int as 1, which I would expect since I wasn't under the impression and recursion was occuring.

Can somebody help me?

How can I view a stack trace? In VS2008 it says: {Cannot evaluate expression because the current thread is in a stack overflow state.}

Best regards,

Robinson

private int cellFormatCallCount = 0;
private void myDataGridView_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e)  {
    try {
        // to format the cell, we will need to know its value and which column its in
        string value = "";
        string column = "";
        
        // the event is sometimes called where the value property is null
        if (e.Value != null) {
            cellFormatCallCount++; // here is my test for recursion, this class member will increment each call

            // This is the line that throws the StackOverflowException
            /* ********************* */
            value = e.Value.ToString();
            /* ********************* */

            column = actionsDataGridView.Columns[e.ColumnIndex].Name;
        } else {
            return; // null values cannont be formatted, so return
        }

        if (column == "id") {
            // different code for formatting each column
        } else if (column == "title") {
            // ...
        } else {
            // ...
        }
    } finally {
        cellFormatCallCount = 0; // after we are done with the formatting, reset our recursion counter
    }
}

Answer 1

Apparently e.Value.ToString() invokes the CellFormatting event again. That seems somewhat logical. It should be easy enough to find out with a debugger.

But the actual recursion could be caused somewhere else, like in the per-column formatting that you omitted.

Your recursion check isn't reliable since Value==null will also reset it, and it appears to be shared by all columns. Make it surround the e.Value.ToString() more tightly:

if (e.Value != null) 
{
   cellFormatCallCount++; 
   System.Diagnostics.Debug.Assert(cellFormatCallCount <= 1, "Recursion");
   value = e.Value.ToString();
   cellFormatCallCount--; 
   ...
} 

Answer 2

Totally random guess (with no stack trace it's all I can do)...

Are you attempting to display/format a type which has a potentially recursive ToString()?

public string ToString()
{
   return ... this.ToString() ...
   // or
   return String.Format("The value is {0}", this);
}

A typo/error like that could cause a StackOverflowException...

Answer 3

Given that this is an event, might it be triggering its self?