异步客户端-服务器套接字错误中的对象处置异常

Question

我正在按照MSDN代码编写异步客户端/服务器套接字。它应该像这样工作：客户端向服务器发送 10 个操作，服务器读取它们，验证它是否可以从帐户中检索资金，执行操作是否有效并将其发送回客户端。

服务器接收操作很好，但是当它发回它们时，客户端会抛出 ObjectDisposedException。服务器套接字是否在客户端读取操作之前关闭？在关闭套接字之前，我是否必须等待客户端读取？

客户端代码：

public class StateObject
{
//Socket del cliente
public Socket workSocket = null;
// Size of receive buffer.  
public const int BufferSize = 1024;
// Receive buffer.  
public byte[] buffer = new byte[BufferSize];
// Received data string.  
public StringBuilder sb = new StringBuilder();
}
public class AsynchronousClient
{
//Puerto para el servidor
//
private const int puerto = 11000;
private static ManualResetEvent connectDone =
new ManualResetEvent(false);
private static ManualResetEvent sendDone =
new ManualResetEvent(false);
private static ManualResetEvent receiveDone =
new ManualResetEvent(false);
//Respuesta del servidor
private static String response = String.Empty;
private static Operacion recibido;
private static void StartClient(Operacion op)
{  
try
{
//Establecemos un endpoint 
IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());
IPAddress ipAddress = ipHostInfo.AddressList[0];
IPEndPoint remoteEP = new IPEndPoint(ipAddress, puerto);
//Creamos el socket del cliente  
Socket client = new Socket(ipAddress.AddressFamily,
SocketType.Stream, ProtocolType.Tcp);
//Nos conectamos al endpoint del servidor  
client.BeginConnect(remoteEP,
new AsyncCallback(ConnectCallback), client);
connectDone.WaitOne();
//Enviamos los datos al servidor  
Send(client, op);
sendDone.WaitOne();
//Recibimos respuesta del servidor  
Receive(client);
receiveDone.WaitOne();
if(recibido.Valido.Equals("false"))
{
Console.WriteLine("No se ha podido proceder con una operación: {0} {1} {2}",
recibido.Origen, recibido.Destino, recibido.Cantidad);
}
//Liberamos el socket
client.Shutdown(SocketShutdown.Both);
client.Close();
}
catch (Exception e)
{
Console.WriteLine("Error: " + e.ToString());
}
}
private static void ConnectCallback(IAsyncResult ar)
{
try
{
Socket client = (Socket)ar.AsyncState;
client.EndConnect(ar);
connectDone.Set();
}
catch (Exception e)
{
Console.WriteLine("Error: " + e.ToString());
}
}
private static void Receive(Socket client)
{
try
{
StateObject state = new StateObject();
state.workSocket = client;
client.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
new AsyncCallback(ReceiveCallback), state);
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
}
private static void ReceiveCallback(IAsyncResult ar)
{
try
{
//Hacemos casting del StateObject y recuperamos el Socket
StateObject state = (StateObject)ar.AsyncState;
Socket client = state.workSocket;
//Leemos los datos del servidor  
int bytesRead = client.EndReceive(ar);
if (bytesRead > 0)
{
//Puede que no hayamos leído todo así que se va añadiendo  
state.sb.Append(Encoding.ASCII.GetString(state.buffer, 0, bytesRead));
//Se recupera lo que falta  
client.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
new AsyncCallback(ReceiveCallback), state);
}
else
{
// All the data has arrived; put it in response.  
if (state.sb.Length > 1)
{
//Deserializacion del objeto
response = state.sb.ToString();
byte[] byteArray = Encoding.ASCII.GetBytes(response);
MemoryStream stream = new MemoryStream(byteArray);
recibido = (Operacion)new XmlSerializer(typeof(Operacion)).Deserialize(stream);
}
// Signal that all bytes have been received.  
receiveDone.Set();
}
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
}
private static void Send(Socket client, Operacion data)
{
XmlSerializer serializer = new XmlSerializer(typeof(Operacion));
Stream stream = new MemoryStream();
serializer.Serialize(stream, data);
byte[] byteData = ((MemoryStream)stream).ToArray();
client.BeginSend(byteData, 0, byteData.Length, 0,
new AsyncCallback(SendCallback), client);
}
private static void SendCallback(IAsyncResult ar)
{
try
{
Socket client = (Socket)ar.AsyncState;
int bytesSent = client.EndSend(ar);
Console.WriteLine("Operaciones enviadas al servidor. {0} bytes enviados.", bytesSent);
sendDone.Set();
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
}
public static int Main(String[] args)
{
for (int i = 0; i < 10; i++)
{
Operacion op = new Operacion("Destino1", "Destino2", 15, "");
StartClient(op);
}
Console.WriteLine("Fin de envío.");
Console.ReadLine();
return 0;
}
}

服务器代码：

public class StateObject
{
// Client  socket.  
public Socket workSocket = null;
// Size of receive buffer.  
public const int BufferSize = 1024;
// Receive buffer.  
public byte[] buffer = new byte[BufferSize];
// Received data string.  
public StringBuilder sb = new StringBuilder();
}
public class AsynchronousSocketListener
{
// Thread signal.  
public static ManualResetEvent allDone = new ManualResetEvent(false);
public static List<Operacion> opList;
private static Dictionary<string, double> listaCuentas;
private static String respuesta = String.Empty;
public AsynchronousSocketListener()
{
}
public static void StartListening()
{
IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());
IPAddress ipAddress = ipHostInfo.AddressList[0];
IPEndPoint localEndPoint = new IPEndPoint(ipAddress, 11000);
Socket listener = new Socket(ipAddress.AddressFamily,
SocketType.Stream, ProtocolType.Tcp);
try
{
listener.Bind(localEndPoint);
listener.Listen(100);
while (true)
{
allDone.Reset();
//Empezamos a escuchar alguna conexión 
Console.WriteLine("Esperando conexión...");
listener.BeginAccept(
new AsyncCallback(AcceptCallback),
listener);
//Esperamos a que la conexión se realice antes de continuar 
allDone.WaitOne();
}
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
Console.WriteLine(opList.ToString());
Console.WriteLine("nPress ENTER to continue...");
Console.Read();
}
public static void AcceptCallback(IAsyncResult ar)
{
allDone.Set();
Socket listener = (Socket)ar.AsyncState;
Socket handler = listener.EndAccept(ar);
StateObject state = new StateObject();
state.workSocket = handler;
handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
new AsyncCallback(ReadCallback), state);
}
public static void ReadCallback(IAsyncResult ar)
{
String cuenta1 = String.Empty;
String cuenta2 = String.Empty;
Double cantidad = 0;
String validez = String.Empty;
StateObject state = (StateObject)ar.AsyncState;
Socket handler = state.workSocket;
int bytesRead = handler.EndReceive(ar);
if (bytesRead > 0)
{
Stream stream = new MemoryStream(state.buffer);
Operacion recibido = (Operacion)new XmlSerializer(typeof(Operacion)).Deserialize(stream);
cuenta1 = recibido.Origen;
cuenta2 = recibido.Destino;
cantidad = recibido.Cantidad;
//Hay que incluir un lock
Console.WriteLine("{0} envía a {1}: {2}", cuenta1, cuenta2, cantidad);
if (cantidad <= listaCuentas[cuenta1])
{
lock(((ICollection)listaCuentas).SyncRoot)
{
Console.WriteLine("Fondos disponibles. Se procede a realizar la operacion.");
recibido.Valido = "true";
listaCuentas[cuenta1] = listaCuentas[cuenta1] - cantidad;
listaCuentas[cuenta2] = listaCuentas[cuenta2] + cantidad;
opList.Add(recibido);
Console.WriteLine("{0}: {1}", cuenta1, listaCuentas[cuenta1]);
Console.WriteLine("{0}: {1}", cuenta2, listaCuentas[cuenta2]);
Send(handler, recibido);
}
} else
{
Console.WriteLine("No hay fondos para realizar la operacion.");
recibido.Valido = "false";
Send(handler, recibido);
}
}
}
private static void Send(Socket handler, Operacion data)
{
XmlSerializer serializer = new XmlSerializer(typeof(Operacion));
Stream stream = new MemoryStream();
serializer.Serialize(stream, data);
byte[] byteData = ((MemoryStream)stream).ToArray(); 
handler.BeginSend(byteData, 0, byteData.Length, 0,
new AsyncCallback(SendCallback), handler);
}
private static void SendCallback(IAsyncResult ar)
{
try
{ 
Socket handler = (Socket)ar.AsyncState;
int bytesEnviados = handler.EndSend(ar);
Console.WriteLine("[0] bytes enviados al cliente.", bytesEnviados);
handler.Shutdown(SocketShutdown.Both);
handler.Close();
}
catch (Exception e)
{
Console.WriteLine("Error: " + e.ToString());
}
}

public static int Main(String[] args)
{
listaCuentas = new Dictionary<string, double>();
listaCuentas.Add("Destino1", 1500 );
listaCuentas.Add("Destino2", 2500);
listaCuentas.Add("Destino3", 150);
listaCuentas.Add("Destino4", 10);
opList = new List<Operacion>();
StartListening();
return 0;
}
}

谢谢！

Answer 1

这是因为您的服务器在客户端确认在 TCP 层收到数据之前关闭了连接。

当字节仍在传输中时，即它们尚未被接收者确认，然后当您关闭套接字时，套接字将发送TCP RESET。 如果所有字节都是ACK'd，则当您关闭套接字时，服务器将经历一个干净的TCP_FIN套接字关闭过程。

这种异常发生在小数据包和TCP DELAYED ACK- 客户端接收字节，它挂在他们寻找更多(延迟它没有确认(，服务器关闭连接，但由于它没有所有的字节 ACKd，它发送一个 RST。 TCP 堆栈挂在那些等待更多字节的字节上，因此没有 ACK 它们，不会使它们可供socket使用。 TCP 堆栈只会使 ACKd 字节可供socket

TLDR;对于快速网络，您需要在服务器端等待250ms才能关闭连接，如果这不是高性能应用程序，那么我建议等待800ms

如 RFC 1122 中所述，TCP 使用延迟确认来减少 在媒体上发送的数据包数。而不是发送 收到的每个 TCP 段的确认，Windows 2000 中的 TCP 然后采用通用方法实现延迟 确认。当 TCP 在特定上接收数据时 连接，仅当其中一个 满足以下条件：未发送确认 上一段收到。接收一个段，但没有收到其他段 在 200 毫秒内到达该连接。