判断socket是否是链接状态

// 检查一个Socket是否可连接
private bool IsSocketConnected(Socket client)
{
    bool blockingState = client.Blocking;
    try
    {
        byte[] tmp = new byte[1];
        client.Blocking = false;
        client.Send(tmp, 0, 0);
        return false;
    }
    catch (SocketException e)
    {
        // 产生 10035 == WSAEWOULDBLOCK 错误，说明被阻止了，但是还是连接的
        if (e.NativeErrorCode.Equals(10035))
            return false;
        else
            return true;
    }
    finally
    {
        client.Blocking = blockingState;    // 恢复状态
    }
}