StackOverflowException without recursion or infinite loop?

Question

Hello,

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

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 2

It's unrelated to the problem but you can actually have a StackOverflowException without recursion at all just with:

throw new StackOverflowException();

Answer 3

@Daniel: If that were the issue, wouldn't it already raise the exception in the line:

if (e.Value != null) {

@gnirts: Could you post the full method and stack trace too?

@BCS (below): I think that might be it, but it might easily be in some of the code that is not shown in the deo posted.

PS. I'm sorry, this should have been a comment, but I have not enough reps :-D

Answer 4

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

Answer 5

Try making the cellFormatCallCount variable static so that it shared by all instances of the class. I suspect that somehow the event is triggering itself but you aren't seeing it because cellFormatCallCount is only local to each instance of the class handling the event and thus is never incremented beyond 1. If that's the case, then the actual trigger for the stackoverflow (recursion) could be anywhere in the method and it just happens to run out of stack space at that line.

Once you've made the variable static, you could throw an exception when it exceeds a certain (small) value, like 2. That exception should leave a viewable stack trace around.

Answer 6

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--; 
   ...
}