.Net的System.Net.Sockets.TcpClient和System.Net.Sockets.Socket都没有直接为Connect/BeginConnect提供超时控制机制。因此，当服务器未处于监听状态，或者发生网络故障时，客户端连接请求会被迫等待很长一段时间，直到抛出异常。默认的等待时间长达20~30s。.Net Socket库的SocketOptionName.SendTimeout提供了控制发送数据的超时时间，但并非本文讨论的连接请求的超时时间。
实现
下面是实现的关键代码：
class TimeOutSocket
{
private static bool IsConnectionSuccessful = false;
private static Exception socketexception;
private static ManualResetEvent TimeoutObject = new ManualResetEvent(false);
public static TcpClient TryConnect(IPEndPoint remoteEndPoint, int timeoutMiliSecond)
{
TimeoutObject.Reset();
socketexception = null;
string serverip = Convert.ToString(remoteEndPoint.Address);
int serverport = remoteEndPoint.Port;
TcpClient tcpclient = new TcpClient();
tcpclient.BeginConnect(serverip, serverport,
new AsyncCallback(CallBackMethod), tcpclient);
if (TimeoutObject.WaitOne(timeoutMiliSecond, false))
{
if (IsConnectionSuccessful)
{
return tcpclient;
}
else
{
throw socketexception;
}
}
else
{
tcpclient.Close();
throw new TimeoutException("TimeOut Exception");
}
}
private static void CallBackMethod(IAsyncResult asyncresult)
{
try
{
IsConnectionSuccessful = false;
TcpClient tcpclient = asyncresult.AsyncState as TcpClient;
if (tcpclient.Client != null)
{
tcpclient.EndConnect(asyncresult);
IsConnectionSuccessful = true;
}
}
catch (Exception ex)
{
IsConnectionSuccessful = false;
socketexception = ex;
}
finally
{
TimeoutObject.Set();
}
}
}