Reproduce async deadlock when attention signals cannot be sent due to network failure.

AsyncDeadlockRepro

using Microsoft.Data.SqlClient;

namespace AsyncCallbackDeadlockTest
{
    internal class Program
    {
        public static void Main(string[] args)
        {
            RunTest("Server=tcp:localhost; Integrated Security=true;");
        }

        public static void RunTest(string connString)
        {
            try
            {
                using var cn = new SqlConnection(connString);
                cn.Open();

                // Repro steps:
                // 1. Set "TdsParserStateObject._enforceTimeoutDelay" to true (introduce timeout trigger delays for rare yet possible situations)
                // 2. Set breakpoint before "SendAttention() in TdsParserStateObject" writes a packet, 
                // 3. Terminate the TCP connection using TCPView or any other tool before attention packet is written.
                // 4. Notice the apps hangs indefinitely.
                
                QueryTimeout(cn).ConfigureAwait(false).GetAwaiter().GetResult();
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message + e.StackTrace);
            }
        }

        private static async Task QueryTimeout(SqlConnection cn)
        {
            try
            {
                var sql = $"WAITFOR DELAY '00:00:02';select 1 as Id;"; // 2 seconds delay followed with select query.

                var command = new SqlCommand(sql, cn)
                {
                    CommandTimeout = 1
                };

                await command.ExecuteReaderAsync().ConfigureAwait(false);
            }
            catch (Exception e)
            {
                Console.WriteLine($"Exception occurred: {e.Message}");
            }
        }
    }
}