Socket.EndReceive（...）不正確返回

Question

我想使用Socket.BeginReceive（...）和Socket.EndReceive（...）作爲我的UDP數據包接收器客戶端。它按預期的方式接收和處理數據包，但是，當我希望取消和關閉套接字時，我實現的Close（）函數在Socket.EndReceive（...）上退出。我假設線程拋出異常，但我無法弄清楚如何捕捉異常以查看問題所在。我之前使用Socket.EndReceive（...），SocketError作爲成功返回。這是一段代碼，顯示了我如何使用套接字。

更新的代碼

void _startReceiving() 
{ 
    _buffer = new byte[Marshal.SizeOf(typeof(EthernetShare.Message))]; 
    _receiveResult = _udpSocket.BeginReceive(_buffer, 0, _buffer.Length, SocketFlags.None, messageProcessor, null); 
} 

private void messageProcessor(IAsyncResult result) 
{ 
    int packetSize = _udpSocket.EndReceive(result); 
    if (packetSize == _buffer.Length) 
    { 
     byte[] packet = _buffer; 
     IAsyncResult asyncResult = result; 
     _startReceiving(); 
     OnMessageReceieved(_buffer.ToStruct<DataStreamingMessage>()); 
    } 
} 
public void Stop() 
{ 

    _continue = false; 
    SocketError error; 
    try 
    { 
     int tmp = _udpSocket.EndReceive(_receiveResult, out error); 

    } 
    catch (Exception) 
    { 

     throw; 
    } 
    _udpSocket.Close(); 
} 

舊代碼

private Socket _udpSocket; 
private byte[] _buffer; 
private IAsyncResult _receiveResult; 
void _startReceiving() 
{ 
    byte[] buffer = new byte[Marshal.SizeOf(typeof(EthernetShare.Message))]; 
    _receiveResult = _udpSocket.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, messageProcessor, null); 
    //_receiveResult = _udpSocket.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, messageProcessor, _continue); 
} 

private void messageProcessor(IAsyncResult result) 
{ 

    //if ((bool)result.AsyncState && result.IsCompleted) 
    if (result.IsCompleted) 
    { 
     _buffer = new byte[Marshal.SizeOf(typeof (EthernetShare.Message))]; 
     //_receiveResult = _udpSocket.BeginReceive(_buffer, 0, _buffer.Length, SocketFlags.None, messageProcessor, _continue); 
     _receiveResult = _udpSocket.BeginReceive(_buffer, 0, _buffer.Length, SocketFlags.None, messageProcessor, null); 
    } 
} 


public void Stop() 
{ 

    _continue = false; 
    SocketError error; 
    try 
    { 
     int tmp = _udpSocket.EndReceive(_receiveResult, out error); 

    } 
    catch (Exception) 
    { 

     throw; 
    } 
    _udpSocket.Close(); 
} 

Answer 1

您使用APM（異步編程模型）是錯誤的。請參閱：http://msdn.microsoft.com/en-us/library/ms228963.aspx

每個對BeginXXX的調用都應該與EndXXX匹配。

在僞代碼，它可能是這個樣子：

private bool isClosed; 
private Socket socket; 

void BeginReceiveNextPacket(){ 
    socket.BeginReceive(..., EndReceiveNextPacket); 
} 

void EndReceiveNextPacket(IAsyncResult result){ 
    try{ 
     // By making a call to EndReceive, we allow the socket to wrap up, close internal handles and raise any exceptions if they exist. 
     socket.EndReceive(result); 

     // Now make a new call to BeginReceive after we invoked the actual call to EndReceive. 
     BeginReceiveNextPacket(); 
    } 
    catch(SocketClosedException) { 
     if (closed){ 
      // We forcefully closed this socket. Therefore, this exception was expected and we can ignore it. 
     } 
     else{ 
      throw; // Catch an unexpected exception. 
     } 
    } 
} 

void Stop(){ 
    isClosed = true; 
    socekt.Close(); 
}