問題原述：

呼叫TcpClient.Connect函式連線其他機器。我在一臺機器上測試程式，對於連線根本無法連線（物理連線不通）的機器，該函式用時5秒左右返回，並捕獲SocketException異常。我在另一臺機器上測試時，Connect函式用時26秒左右的時間才返回。請問有沒有方法設定Connect函式連線超時的時間，如果超過一定時間還沒有連上則返回。

解決方法：

   寫了個幫助類，用了執行緒池   
    
class TcpClientConnector { /// <summary> /// 在指定時間內嘗試連線指定主機上的指定埠。 /// </summary> /// <param name="hostname">要連線到的遠端主機的 DNS 名。</param> /// <param name="port">要連線到的遠端主機的埠號。</param> /// <param name="millisecondsTimeout">要等待的毫秒數，或 -1 表示無限期等待。</param> /// <returns>已連線的一個 TcpClient 例項。</returns> /// <remarks>本方法可能丟擲的異常與 TcpClient 的建構函式過載之一 /// public TcpClient(string, int) 相同，並若指定的等待時間是個負數且不等於 /// -1，將會丟擲 ArgumentOutOfRangeException。</remarks> public static TcpClient Connect(string hostname, int port, int millisecondsTimeout) { ConnectorState cs = new ConnectorState(); cs.Hostname = hostname; cs.Port = port; ThreadPool.QueueUserWorkItem(new WaitCallback(ConnectThreaded), cs); if (cs.Completed.WaitOne(millisecondsTimeout, false)) { if (cs.TcpClient != null) return cs.TcpClient; throw cs.Exception; } else { cs.Abort(); throw new SocketException(11001); // cannot connect } } private static void ConnectThreaded(object state) { ConnectorState cs = (ConnectorState)state; cs.Thread = Thread.CurrentThread; try { TcpClient tc = new TcpClient(cs.Hostname, cs.Port); if (cs.Aborted) { try { tc.GetStream().Close(); } catch { } try { tc.Close(); } catch { } } else { cs.TcpClient = tc; cs.Completed.Set(); } } catch (Exception e) { cs.Exception = e; cs.Completed.Set(); } } private class ConnectorState { public string Hostname; public int Port; public volatile Thread Thread; public readonly ManualResetEvent Completed = new ManualResetEvent(false); public volatile TcpClient TcpClient; public volatile Exception Exception; public volatile bool Aborted; public void Abort() { if (Aborted != true) { Aborted = true; try { Thread.Abort(); } catch { } } } } }

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  用法示例：   
   
try { Console.WriteLine("Connecting to nonexistenthost..."); TcpClient tc = TcpClientConnector.Connect("nonexistent", 80, 1000); Console.WriteLine("Returned"); try { tc.GetStream().Close(); } catch { } try { tc.Close(); } catch { } } catch (Exception e) { Console.WriteLine("Exception: " + e.Message); }