Conn.Open() still work after SQL Service is stopped

Question

I have met a issue with sql server 2005 SP2, I have created a windows form and with a button on it, and with the following steps:

1. Make sure Sql service is running, then click the button, everything is OK
2. Stop the Sql service, and then click the button again, on my machine, there is not exception at the code of LINE 1, exception occurred at LINE 2, and this is the exception info:

Message: A transport-level error has occurred when sending the request to the server. (provider: Shared Memory Provider, error: 0 - No process is on the other end of the pipe.)

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace ReconnectSQL
{
    public partial class Form1 : Form
    {

        private string m_ConnectionString = @"Server=(local); Database=testDB; User ID=sa; Password=admins; Connection Timeout=15";

        public Form1()
        {
            InitializeComponent();
        }

        /// <summary>
        /// 
        /// </summary>
        public DataTable GetByFillDataTable()
        {
            try
            {
                SqlCommand cmd = new SqlCommand("getalldata");
                cmd.CommandType = CommandType.StoredProcedure;

                DataTable dt = this.GetDataTable(cmd);
                return dt;
            }
            catch
            {
                throw;
            }
        }


        #region common funcs
        /// <summary>
        /// 
        /// </summary>
        /// <param name="cmd"></param>
        /// <returns></returns>
        private DataTable GetDataTable(SqlCommand cmd)
        {
            DataTable dt = new DataTable();

            using (SqlConnection conn = new SqlConnection(this.m_ConnectionString))
            {
                try
                {
                    conn.Open();  // LINE 1
                }
                catch (Exception eX)
                {
                    throw;
                }

                using (SqlDataAdapter adapter = new SqlDataAdapter())
                {
                    try
                    {
                        cmd.Connection = conn;
                        cmd.CommandTimeout = conn.ConnectionTimeout;
                        adapter.SelectCommand = cmd;
                        adapter.Fill(dt);  // LINE 2
                    }
                    catch (Exception eX)
                    {
                        throw;
                    }
                }
            }

            return dt;
        }

        #endregion       

        private void button2_Click(object sender, EventArgs e)
        {

            try
            {
                DataTable dt = GetByFillDataTable();
                listBox1.Items.Add("GetByFillDataTable is called without exceptions!");
            }
            catch (Exception ex)
            {
                listBox1.Items.Add(ex.Message);
            }            }
    }
}

Detailed exception info:

-       [System.Data.SqlClient.SqlException]    {"A transport-level error has occurred when sending the request to the server. (provider: Shared Memory Provider, error: 0 - No process is on the other end of the pipe.)"} System.Data.SqlClient.SqlException
+       base    {"A transport-level error has occurred when sending the request to the server. (provider: Shared Memory Provider, error: 0 - No process is on the other end of the pipe.)"} System.Data.Common.DbException {System.Data.SqlClient.SqlException}
        Class   20  byte
+       Errors  {System.Data.SqlClient.SqlErrorCollection}  System.Data.SqlClient.SqlErrorCollection
        LineNumber  0   int
        Number  233 int
        Procedure   null    string
        Server  "(local)"   string
        Source  ".Net SqlClient Data Provider"  string
        State   0   byte

StackTrace

at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)
   at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)
   at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj)
   at System.Data.SqlClient.TdsParserStateObject.WriteSni()
   at System.Data.SqlClient.TdsParserStateObject.WritePacket(Byte flushMode)
   at System.Data.SqlClient.TdsParserStateObject.ExecuteFlush()
   at System.Data.SqlClient.TdsParser.TdsExecuteRPC(_SqlRPC[] rpcArray, Int32 timeout, Boolean inSchema, SqlNotificationRequest notificationRequest, TdsParserStateObject stateObj, Boolean isCommandProc)
   at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
   at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)
   at System.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior)
   at System.Data.Common.DbCommand.System.Data.IDbCommand.ExecuteReader(CommandBehavior behavior)
   at System.Data.Common.DbDataAdapter.FillInternal(DataSet dataset, DataTable[] datatables, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior)
   at System.Data.Common.DbDataAdapter.Fill(DataTable[] dataTables, Int32 startRecord, Int32 maxRecords, IDbCommand command, CommandBehavior behavior)
   at System.Data.Common.DbDataAdapter.Fill(DataTable dataTable)
   at ReconnectSQL.Form1.GetDataTable(SqlCommand cmd) in E:\_public_\sqlFail\ReconnectSQL\ReconnectSQL\Form1.cs:line 138

Answer 1

After some investigations, it seems the connection still exist in the connection pool even sql is stopped, so after sql is started and by calling conn.Open() it get the connection object from the pool which should be invalid, then the SqlDataAdapter.Fill cause the exception

http://social.msdn.microsoft.com/Forums/en-US/adodotnetdataproviders/thread/99963999-a59b-4614-a1b9-869c6dff921e