public ArrayList GetClientList()//获取客户端列表
 {
     ArrayList client_list = new ArrayList();
     IP_Port ip_port;
     if (clients.Count == 0) return null;
     foreach (Object obj in clients)
     {
         Client client = (Client)obj;
         ip_port = new IP_Port(client.IP_addr, client.Port);
         client_list.Add(ip_port);
     }
     return client_list;
 }
 public int Send(string IP_addr, int port, byte[] bytes, int length)//发送数据到客户端
 {
     if (clients.Count == 0) return -1;
     IP_Port ip_port = new IP_Port(IP_addr, port);
     int index = clients.IndexOf(ip_port);
     if (index < 0) return -1;
     Client client = (Client)clients[index];
     client.socket.BeginSend(bytes, 0, length, 0, new AsyncCallback(SendCallback), client);
     return length;
 }