SOCKET 异步 连接过多时无法连接 C#

Question

Socket.Listen(int backlog)可以指定等待连接的队列长度，根据操作系统的不同，backlog 参数被限制为不同的值。您可以指定更大的值，但 backlog 将受操作系统的限制。默认是系统允许的最大值MaxConnections
另外，用异步处理，多半是每个连接独立线程，线程那么多，也会影响效率
就好像在搞DDOS攻击

Answer 1

我指定的backlog是1w， 不小了吧？ 我用的异步， 但是只用一个线程（底层怎么实现的我就不知道了）是不是accept的太慢了， 导致连接被挂起来了？

Answer 2

代码来喽！ 我也是下别人的
 /// <summary>
    /// 基于SocketAsyncEventArgs 实现 IOCP 服务器
    /// </summary>
    internal sealed class IoServer
    {
        /// <summary>
        /// 监听Socket，用于接受客户端的连接请求
        /// </summary>
        private Socket listenSocket;        /// <summary>
        /// 用于服务器执行的互斥同步对象
        /// </summary>
        private static Mutex mutex = new Mutex();        /// <summary>
        /// 用于每个I/O Socket操作的缓冲区大小
        /// </summary>
        private Int32 bufferSize;        /// <summary>
        /// 服务器上连接的客户端总数
        /// </summary>
        private Int32 numConnectedSockets;        /// <summary>
        /// 服务器能接受的最大连接数量
        /// </summary>
        private Int32 numConnections;        /// <summary>
        /// 完成端口上进行投递所用的IoContext对象池
        /// </summary>
        private IoContextPool ioContextPool;        public MainForm mainForm;        /// <summary>
        /// 构造函数，建立一个未初始化的服务器实例
        /// </summary>
        /// <param name="numConnections">服务器的最大连接数据</param>
        /// <param name="bufferSize"></param>
        internal IoServer(Int32 numConnections, Int32 bufferSize)
        {
            this.numConnectedSockets = 0;
            this.numConnections = numConnections;
            this.bufferSize = bufferSize;            this.ioContextPool = new IoContextPool(numConnections);            // 为IoContextPool预分配SocketAsyncEventArgs对象
            for (Int32 i = 0; i < this.numConnections; i++)
            {
                SocketAsyncEventArgs ioContext = new SocketAsyncEventArgs();
                ioContext.Completed += new EventHandler<SocketAsyncEventArgs>(OnIOCompleted);
                ioContext.SetBuffer(new Byte[this.bufferSize], 0, this.bufferSize);                // 将预分配的对象加入SocketAsyncEventArgs对象池中
                this.ioContextPool.Add(ioContext);
            }
        }        /// <summary>
        /// 当Socket上的发送或接收请求被完成时，调用此函数
        /// </summary>
        /// <param name="sender">激发事件的对象</param>
        /// <param name="e">与发送或接收完成操作相关联的SocketAsyncEventArg对象</param>
        private void OnIOCompleted(object sender, SocketAsyncEventArgs e)
        {
            // Determine which type of operation just completed and call the associated handler.
            switch (e.LastOperation)
            {
                case SocketAsyncOperation.Receive:
                    this.ProcessReceive(e);
                    break;
                case SocketAsyncOperation.Send:
                    this.ProcessSend(e);
                    break;
                default:
                    throw new ArgumentException("The last operation completed on the socket was not a receive or send");
            }
        }        /// <summary>
        ///接收完成时处理函数
        /// </summary>
        /// <param name="e">与接收完成操作相关联的SocketAsyncEventArg对象</param>
        private void ProcessReceive(SocketAsyncEventArgs e)
        {
            // 检查远程主机是否关闭连接
            if (e.BytesTransferred > 0)
            {
                if (e.SocketError == SocketError.Success)
                {
                    Socket s = (Socket)e.UserToken;
                    //判断所有需接收的数据是否已经完成
                    if (s.Available == 0)
                    {
                        byte[] buffer = new byte[e.BytesTransferred];
                        Array.Copy(e.Buffer, buffer, e.BytesTransferred);
                        string str = Encoding.ASCII.GetString(buffer);                        MainForm.lBps += str.Length;                        // 设置发送数据
                        Array.Copy(e.Buffer, 0, e.Buffer, e.BytesTransferred, e.BytesTransferred);
                        e.SetBuffer(e.Offset, e.BytesTransferred * 2);
                        if (!s.SendAsync(e))        //投递发送请求，这个函数有可能同步发送出去，这时返回false，并且不会引发SocketAsyncEventArgs.Completed事件
                        {
                            // 同步发送时处理发送完成事件
                            this.ProcessSend(e);
                        }
                    }
                    else if (!s.ReceiveAsync(e))    //为接收下一段数据，投递接收请求，这个函数有可能同步完成，这时返回false，并且不会引发SocketAsyncEventArgs.Completed事件
                    {
                        // 同步接收时处理接收完成事件
                        this.ProcessReceive(e);
                    }
                }
                else
                {
                    this.ProcessError(e);
                }
            }
            else
            {
                this.CloseClientSocket(e);
            }
        }        /// <summary>
        /// 发送完成时处理函数
        /// </summary>
        /// <param name="e">与发送完成操作相关联的SocketAsyncEventArg对象</param>
        private void ProcessSend(SocketAsyncEventArgs e)
        {
            if (e.SocketError == SocketError.Success)
            {
                Socket s = (Socket)e.UserToken;                //接收时根据接收的字节数收缩了缓冲区的大小，因此投递接收请求时，恢复缓冲区大小
                e.SetBuffer(0, bufferSize);
                if (!s.ReceiveAsync(e))     //投递接收请求
                {
                    // 同步接收时处理接收完成事件
                    this.ProcessReceive(e);
                }
            }
            else
            {
                this.ProcessError(e);
            }
        }        /// <summary>
        /// 处理socket错误
        /// </summary>
        /// <param name="e"></param>
        private void ProcessError(SocketAsyncEventArgs e)
        {
            Socket s = e.UserToken as Socket;
            IPEndPoint localEp = s.LocalEndPoint as IPEndPoint;            this.CloseClientSocket(s, e);            string outStr = String.Format("套接字错误 {0}, IP {1}, 操作 {2}。", (Int32)e.SocketError, localEp, e.LastOperation);
            mainForm.Invoke(mainForm.setlistboxcallback, outStr);
            //Console.WriteLine("Socket error {0} on endpoint {1} during {2}.", (Int32)e.SocketError, localEp, e.LastOperation);
        }        /// <summary>
        /// 关闭socket连接
        /// </summary>
        /// <param name="e">SocketAsyncEventArg associated with the completed send/receive operation.</param>
        private void CloseClientSocket(SocketAsyncEventArgs e)
        {
            Socket s = e.UserToken as Socket;
            this.CloseClientSocket(s, e);
        }        private void CloseClientSocket(Socket s, SocketAsyncEventArgs e)
        {
            Interlocked.Decrement(ref this.numConnectedSockets);            // SocketAsyncEventArg 对象被释放，压入可重用队列。
            this.ioContextPool.Push(e);            
            string outStr = String.Format("客户 {0} 断开, 共有 {1} 个连接。", s.RemoteEndPoint.ToString(), this.numConnectedSockets);
            mainForm.Invoke(mainForm.setlistboxcallback, outStr);            
            //Console.WriteLine("A client has been disconnected from the server. There are {0} clients connected to the server", this.numConnectedSockets);
            try
            {
                s.Shutdown(SocketShutdown.Send);
            }
            catch (Exception)
            {
                // Throw if client has closed, so it is not necessary to catch.
            }
            finally
            {
                s.Close();
            }
        }

Answer 3

        /// <summary>
        /// accept 操作完成时回调函数
        /// </summary>
        /// <param name="sender">Object who raised the event.</param>
        /// <param name="e">SocketAsyncEventArg associated with the completed accept operation.</param>
        private void OnAcceptCompleted(object sender, SocketAsyncEventArgs e)
        {
            this.ProcessAccept(e);
        }        /// <summary>
        /// 监听Socket接受处理
        /// </summary>
        /// <param name="e">SocketAsyncEventArg associated with the completed accept operation.</param>
        private void ProcessAccept(SocketAsyncEventArgs e)
        {
            Socket s = e.AcceptSocket;
            if (s.Connected)
            {
                try
                {
                    SocketAsyncEventArgs ioContext = this.ioContextPool.Pop();
                    if (ioContext != null)
                    {
                        // 从接受的客户端连接中取数据配置ioContext
                        ++MainForm.lAll;                        ioContext.UserToken = s;
                        Interlocked.Increment(ref MainForm.lCount);
                        Interlocked.Increment(ref this.numConnectedSockets);
                        //string outStr = String.Format("客户 {0} 连入, 共有 {1} 个连接。",  s.RemoteEndPoint.ToString(),this.numConnectedSockets);
                        //mainForm.Invoke(mainForm.setlistboxcallback,outStr);
                        //Console.WriteLine("Client connection accepted. There are {0} clients connected to the server",
                            //this.numConnectedSockets);                        if (!s.ReceiveAsync(ioContext))
                        {
                            this.ProcessReceive(ioContext);
                        }
                    }
                    else        //已经达到最大客户连接数量，在这接受连接，发送“连接已经达到最大数”，然后断开连接
                    {
                        s.Send(Encoding.Default.GetBytes("连接已经达到最大数!"));
                        string outStr = String.Format("连接已满，拒绝 {0} 的连接。", s.RemoteEndPoint);
                        mainForm.Invoke(mainForm.setlistboxcallback, outStr);
                        s.Close();
                   }
                }
                catch (SocketException ex)
                {
                    Socket token = e.UserToken as Socket;
                    string outStr = String.Format("接收客户 {0} 数据出错, 异常信息： {1} 。", token.RemoteEndPoint, ex.ToString());
                    mainForm.Invoke(mainForm.setlistboxcallback, outStr);
                    //Console.WriteLine("Error when processing data received from {0}:\r\n{1}", token.RemoteEndPoint, ex.ToString());
                }
                catch (Exception ex)
                {
                    mainForm.Invoke(mainForm.setlistboxcallback, "异常：" + ex.ToString());
                }
                // 投递下一个接受请求
                this.StartAccept(e);
            }
        }        /// <summary>
        /// 从客户端开始接受一个连接操作
        /// </summary>
        /// <param name="acceptEventArg">The context object to use when issuing 
        /// the accept operation on the server's listening socket.</param>
        private void StartAccept(SocketAsyncEventArgs acceptEventArg)
        {
            if (acceptEventArg == null)
            {
                acceptEventArg = new SocketAsyncEventArgs();
                acceptEventArg.Completed += new EventHandler<SocketAsyncEventArgs>(OnAcceptCompleted);
            }
            else
            {
                // 重用前进行对象清理
                acceptEventArg.AcceptSocket = null;
            }            if (!this.listenSocket.AcceptAsync(acceptEventArg))
            {
                this.ProcessAccept(acceptEventArg);
            }
        }        /// <summary>
        /// 启动服务，开始监听
        /// </summary>
        /// <param name="port">Port where the server will listen for connection requests.</param>
        internal void Start(Int32 port)
        {
            // 获得主机相关信息
            IPAddress[] addressList = Dns.GetHostEntry(Environment.MachineName).AddressList;
            IPEndPoint localEndPoint = new IPEndPoint(IPAddress.Parse("192.168.0.253"), 55001);//addressList[addressList.Length - 1], port);            // 创建监听socket
            this.listenSocket = new Socket(localEndPoint.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
            this.listenSocket.ReceiveBufferSize = this.bufferSize;
            this.listenSocket.SendBufferSize = this.bufferSize;            this.listenSocket.Bind(localEndPoint);            // 开始监听
            this.listenSocket.Listen(this.numConnections);            // 在监听Socket上投递一个接受请求。
            this.StartAccept(null);            // Blocks the current thread to receive incoming messages.
            mutex.WaitOne();
        }        /// <summary>
        /// 停止服务
        /// </summary>
        internal void Stop()
        {
            this.listenSocket.Close();
            mutex.ReleaseMutex();
        }    } /// <summary>
    /// 与每个客户Socket相关联，进行Send和Receive投递时所需要的参数
    /// </summary>
    internal sealed class IoContextPool
    {
        List<SocketAsyncEventArgs> pool;        //为每一个Socket客户端分配一个SocketAsyncEventArgs，用一个List管理，在程序启动时建立。
        Int32 capacity;                         //pool对象池的容量
        Int32 boundary;                         //已分配和未分配对象的边界，大的是已经分配的，小的是未分配的        internal IoContextPool(Int32 capacity)
        {
            this.pool = new List<SocketAsyncEventArgs>(capacity);
            this.boundary = 0;
            this.capacity = capacity;
        }        /// <summary>
        /// 往pool对象池中增加新建立的对象，因为这个程序在启动时会建立好所有对象，
        /// 故这个方法只在初始化时会被调用,因此，没有加锁。
        /// </summary>
        /// <param name="arg"></param>
        /// <returns></returns>
        internal bool Add(SocketAsyncEventArgs arg)
        {
            if (arg != null && pool.Count < capacity)
            {
                pool.Add(arg);
                boundary++;
                return true;
            }
            else
                return false;
        }        /// <summary>
        /// 取出集合中指定对象，内部使用
        /// </summary>
        /// <param name="index"></param>
        /// <returns></returns>
        //internal SocketAsyncEventArgs Get(int index)
        //{
        //    if (index >= 0 && index < capacity)
        //        return pool[index];
        //    else
        //        return null;
        //}        /// <summary>
        /// 从对象池中取出一个对象，交给一个socket来进行投递请求操作
        /// </summary>
        /// <returns></returns>
        internal SocketAsyncEventArgs Pop()
        {
            lock (this.pool)
            {
                if (boundary > 0)
                {
                    --boundary;
                    return pool[boundary];
                }
                else
                    return null;
            }
        }        /// <summary>
        /// 一个socket客户断开，与其相关的IoContext被释放，重新投入Pool中，备用。
        /// </summary>
        /// <param name="arg"></param>
        /// <returns></returns>
        internal bool Push(SocketAsyncEventArgs arg)
        {
            if (arg != null)
            {
                lock (this.pool)
                {
                    int index = this.pool.IndexOf(arg, boundary);  //找出被断开的客户,此处一定能查到，因此index不可能为-1，必定要大于0。
                    if (index == boundary)         //正好是边界元素
                        boundary++;
                    else
                    {
                        this.pool[index] = this.pool[boundary];     //将断开客户移到边界上，边界右移
                        this.pool[boundary++] = arg;
                    }
                }
                return true;
            }
            else
                return false;
        }
    }private IoServer iocp = new IoServer(10000, 10240);
iocp.Start(55001);

Answer 4

private IoServer iocp = new IoServer(10000, 10240);
你的缓冲区设太小了，调大一些试试看。
private IoServer iocp = new IoServer(10000, 1024*1024);

Answer 5

前段时间研究了一下,卡在了双工通信的发送操作上,我想设置两个异步操作池,一个用于接收,一个用于发送,但发现不好实现数据发送的功能,感觉要先做一个发送缓冲队列,要发送的数据压入这个队列(主要是发送操作的buffer大小是固定的,但发送的数据可能会超过这个大小,需要手动分拆,这块我没法写出优雅的代码,感觉很乱),不知有没有高人指点一二?

Answer 6

我模拟的客户端有读数据库， 我邮箱：[email protected]

Answer 7

我用的就是MSDN上的示例代码，BTW，你那段代码其实也是MSDN的示例。有数据库读取的话，怀疑还是缓冲区不够，导致服务端来不及处理。

Answer 8

var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
socket.Bind(new IPEndPoint(IPAddress.Any, int.Parse(txt_port.Text)));
socket.Listen(10000);
socket.BeginAccept(new AsyncCallback(ClientAccepted), socket);
 public void ClientAccepted(IAsyncResult ar)
 {
            var socket = ar.AsyncState as Socket;
 }
我这连接1W个 没什么问题..