NullReferenceException，C# 套接字 BeginConnect 中的错误

我们有一个通过TCP套接字与客户端通信的服务器应用程序。运行几周后，它会崩溃，并显示无法处理的 NullReferenceException。我已经能够使用非常小的控制台程序重现异常，但内部套接字线程池中似乎存在未处理的异常。所以我无法使用任何尝试/捕获块来处理它，因为它不在我的控制范围内。

有人对此有任何想法吗？这是一个框架错误，还是我如何在套接字线程池上捕获异常（所以我们的应用程序不会崩溃）？下面是在几次迭代 （3-10） 后生成异常的示例代码。重要的是要知道服务器处于脱机状态，因此套接字无法连接。它使用的是Visual studio 2010和.Net框架4.0。

internal class Program
{
    private static string host;
    private static Socket socket;
    private static void Main(string[] args)
    {
        Trace.Listeners.Add(new ConsoleTraceListener());
        AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException);
        socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        host = "127.0.0.1";
        //aslo the problem is happening whe the host is other network ip address
        //host = "192.168.0.1";
        //when in other thread doesn not crash application
        //Task.Factory.StartNew(() => StartConnecting());
        //also crashing the application
        //Task.Factory.StartNew(() => StartConnecting(), TaskCreationOptions.LongRunning);
        //when it is regular thread the exception occurs
        ///*
        var thread = new Thread(new ThreadStart(StartConnecting));
        thread.Start();
        //*/
        //when it is blocking exception also occurs
        //StartConnecting();
        Console.WriteLine("Press any key to exit ...");
        Console.ReadKey();
    }
    private static void StartConnecting()
    {
        try
        {
            int count = 0;
            while (true)
            {
                try
                {
                    // if i must switch to Socket.Connect(...)?
                    Trace.WriteLine(string.Format("Connect Try {0} begin", ++count));
                    var ar = socket.BeginConnect(host, 6500, new AsyncCallback(ConnectCallback), socket);
                    Trace.WriteLine(string.Format("Connect Try {0} end", count));
                }
                catch (Exception err)
                {
                    Trace.WriteLine(string.Format("[BeginConnect] error {0}", err.ToString()));
                }
                System.Threading.Thread.Sleep(1000);
                //will see the exception more quick
            }
        }
        catch (Exception e)
        {
            Trace.WriteLine(string.Format("[StartConnecting] error {0}", e.ToString()));
        }
    }
    private static void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
    {
        string msg = e.ExceptionObject.ToString();
        Trace.WriteLine(string.Format("[CurrentDomain_UnhandledException] isTerminating={0} error {1}", e.IsTerminating, msg));
        Trace.WriteLine("Exiting process");
        //the other processing threads continue working
        //without problems untill there is thread.sleep
        //Thread.Sleep(10000);
    }
    private static void ConnectCallback(IAsyncResult ar)
    {
        try
        {
            Trace.WriteLine("[ConnectCallback] enter");
            var socket = (Socket)ar.AsyncState;
            socket.EndConnect(ar);
            Trace.WriteLine("[ConnectCallback] exit");
        }
        catch (Exception e)
        {
            Trace.WriteLine(string.Format("[ConnectCallback] error {0}", e.ToString()));
        }
    }
}

应用程序启动后，将发生不可避免的崩溃：

[CurrentDomain_UnhandledException] isTerminating=True error System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Net.Sockets.Socket.ConnectCallback()
   at System.Net.Sockets.Socket.RegisteredWaitCallback(Object state, Boolean timedOut)
   at System.Threading._ThreadPoolWaitOrTimerCallback.PerformWaitOrTimerCallback(Object state, Boolean timedOut)