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,它会因无法处理的 NullReferenceException 而崩溃。我已经能够用一个非常小的控制台程序重现异常,但似乎在内部套接字线程池中存在未处理的异常。所以我不能用任何 try/catch block 来处理它,因为它不在我的控制之下。
有没有人对此有任何想法?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(这样我们的应用程序就不会崩溃)? 这是在几次迭代 (3-10) 之后生成异常的示例代码。重要的是要知道服务器处于离线状态,因此套接字无法连接。使用Visual Studio 2010和.Net Framework 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()));
}
}
}
应用程序启动后不可避免的会发生崩溃:
[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)
最佳答案
您提供的示例代码在不等待异步操作完成的情况下重复调用 BeginConnect
。
粗略地说,你正在这样做
while(true)
{
socket.BeginConnect(...);
Sleep(1000);
}
因此,当您的线程启动时,它首先调用 BeginConnect()
,然后等待一秒钟,然后在前一个调用仍在执行时再次调用 BeginConnect()
。
在我的电脑上,它给了我一个 InvalidOperationException
,但我猜异常类型可能取决于 CLR 版本(我使用的是 .NET 4.5.1)。
这里有 3 种不同的解决方案:
- 使用
Socket.EndConnect()
取消异步操作 - 使用
IAsyncResult.AsyncWaitHandle.WaitOne()
等待异步操作完成 - 不要使用
BeginConnect()
而是使用Connect()
关于c# - NullReferenceException,C# 套接字 BeginConnect 中的错误?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/19524199/