StackOverflow in VB.NET SQLite query

Question

I have an StackOverflowException in one of my DB functions that I don't know how to deal with. I have a SQLite database with one table "tblEmployees" that holds records for each employees (several thousand posts) and usually this function runs without any problem.

But sometimes after the the function is called a thousand times it breaks with an StackOverflowException at the line "ReturnTable.Load(reader)" with the message: An unhandled exception of type 'System.StackOverflowException' occurred in System.Data.SQLite.dll

If I restart the application it has no problem to continue with the exact same post it last crashed on. I can also make the exactly same DB-call from SQLite Admin at the crash time without no problems.

Here is the code:

Public Function GetNextEmployeeInQueue() As String
    Dim NextEmployeeInQueue As String = Nothing
    Dim query As [String] = "SELECT FirstName FROM tblEmployees WHERE Checked=0 LIMIT 1;"
    Try
        Dim ReturnTable As New DataTable()
        Dim mycommand As New SQLiteCommand(cnn)
        mycommand.CommandText = query
        Dim reader As SQLiteDataReader = mycommand.ExecuteReader()
        ReturnTable.Load(reader)
        reader.Close()
        If ReturnTable.Rows.Count > 0 Then
            NextEmployeeInQueue = ReturnTable.Rows(0)("FirstName").ToString()
        Else
            MsgBox("No more employees found in queue")
        End If
    Catch fail As Exception
        MessageBox.Show("Error: " & fail.Message.ToString())
    End Try
    If NextEmployeeInQueue IsNot Nothing Then
        Return NextEmployeeInQueue
    Else
        Return "No more records in queue"
    End If
End Function

When crashes, the reader has "Property evaluation failed." in all values.

I assume there is some problem with allocated memory that isn't released correctly, but can't figure out what object it's all about. The DB-connection opens when the DB-class object is created and closes on main form Dispose.

Should I maybe dispose the mycommand object every time in a finally block? But wouldn't that result in a closed DB-connection?

Answer 1

It's hard to be sure without the stack trace, but I'd imagine that somewhere you have a recursive call to a function that increases the call stack size on each iteration. The StackOverflowException error comes from the SQLite library, but I suspect that most of the calls on the stack at this point are your own functions. The call into the SQLite library was the call that broke the camel's back, but that's not necessarily where the error is.

Post the (interesting parts of the) stack trace and perhaps we can tell you more precisely where your error is.