C# Socket连接请求超时机制实现代码分享

.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*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();
        }
    }
}