Question

I have a Windows Forms app in C#/.NET4 with a SQL 2008 back end. I open a SqlConnection in my button click event handler, then call multiple backgroundworkers each of which calls the connection’s CreateCommand method inside of a using block:

    private void btnSubmit_Click(object sender, EventArgs e)
    {
        cn.Open();
        bw01.RunWorkerAsync(x);
        bw02.RunWorkerAsync(x);
        while (bw01.IsBusy || bw02.IsBusy)
            Application.DoEvents();
        cn.Close();
    }

    private void bw01_DoWork(object sender, DoWorkEventArgs e)
    {
        try
        {
            using (SqlCommand cmd = cn.CreateCommand())
            {
                cmd.CommandText = <some SQL>
                e.Result = Convert.ToInt32(cmd.ExecuteScalar());
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
            return;
        }
    }

    private void bw02_DoWork(object sender, DoWorkEventArgs e)
    {
        try
        {
            using (SqlCommand cmd = cn.CreateCommand())
            {
                cmd.CommandText = <some SQL>
                e.Result = Convert.ToInt32(cmd.ExecuteScalar());
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
            return;
        }
    }

The code works some of the time, but other times I get errors, most commonly “A severe error occurred on the current command. The results if any should be discarded.”

I have MultipleActiveResultSets=true in my connection string. What am I doing wrong?

Answer 1

You connection variable is not thread safe as both threads are trying to use it. ADO.NET will manage connection pool for you so you should move connection creation inside each thread and make it atomic