介绍

默认情况下，建立的套接字都是阻塞的，程序会停在等待网络事件的地方（accept），直到网络io条件满足，才会继续向下执行
image.png

代码实现

  1. #include <WinSock2.h>
  2. #include <Windows.h>
  3. #include <WS2tcpip.h>
  4. #include <stdlib.h>
  5. #include <stdio.h>
  8. #pragma comment(lib,"ws2_32.lib")
  10. #define DEFAULT_BUFLEN 512
  11. #define DEFAULT_PORT    27015
  14. int __cdecl main(int argc,TCHAR* argv[]) {
  15.     WSADATA wsaData;
  16.     int iResult;
  17.     SOCKET ServerSocket = INVALID_SOCKET;
  18.     SOCKET AcceptSocket = INVALID_SOCKET;
  19.     char recvbuf[DEFAULT_BUFLEN];
  20.     int recvBufLen = DEFAULT_BUFLEN;
  21.     sockaddr_in addrClient;
  22.     int addrClinetLen = sizeof(sockaddr_in);
  24.     iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
  25.     if (iResult!=0)
  26.     {
  27.         printf_s("wsatartup faild with error code %d\n", iResult);
  28.         return 1;
  29.     }
  31.     ServerSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_IP);
  32.     if (ServerSocket==INVALID_SOCKET)
  33.     {
  34.         printf_s("SOCKET FAILED WITH ERROR CODE %d",WSAGetLastError());
  35.         WSACleanup();
  36.         return 1;
  38.     }
  39.     SOCKADDR_IN addrServ;
  40.     addrServ.sin_family = AF_INET;
  41.     addrServ.sin_port = htons(DEFAULT_PORT);
  42.     addrServ.sin_addr.S_un.S_addr = htonl(INADDR_ANY);
  43.     iResult = bind(ServerSocket,(const struct sockaddr*)&addrServ,sizeof(SOCKADDR_IN));
  45.     if (iResult==SOCKET_ERROR)
  46.     {
  47.         printf_s("bind falied with error code %d\n",iResult);
  48.         closesocket(ServerSocket);
  49.         WSACleanup();
  50.         return 1;
  51.     }
  52.     iResult = listen(ServerSocket,SOMAXCONN);
  54.     if (iResult==SOCKET_ERROR)
  55.     {
  56.         printf_s("listen failed with error code %d",iResult);
  57.         closesocket(ServerSocket);
  58.         WSACleanup();
  59.         return -1;
  61.     }
  62.     printf_s("TCP server starting");
  65.     int err;
  66.     while (true)
  67.     {
  68.         AcceptSocket = accept(ServerSocket, (sockaddr FAR*) & addrClient, &addrClinetLen);
  69.         if (AcceptSocket == INVALID_SOCKET)
  70.         {
  73.             printf_s("accetp failed \n");
  74.             closesocket(ServerSocket);
  75.             WSACleanup();
  76.             return 1;
  78.         }
  79.         while (true)
  80.         {
  81.             memset(recvbuf, 0, recvBufLen);
  82.             iResult = recv(AcceptSocket, recvbuf, recvBufLen, 0);
  84.             if (iResult>0)
  85.             {
  86.                 printf_s("recv data %d byte\n",iResult);
  87.                 int iSendResult = send(AcceptSocket, recvbuf, iResult, 0);
  88.                 if (iSendResult == SOCKET_ERROR) {
  89.                     printf("send failed with error: %d\n", WSAGetLastError());
  90.                     closesocket(AcceptSocket);
  91.                     WSACleanup();
  92.                     return 1;
  93.                 }
  94.                 printf("Bytes sent: %d\n", iSendResult);
  95.                 continue;
  97.             }
  98.             else if (iResult == 0)
  99.             {
  100.                 printf_s("conn closeing ....\n");
  101.                 closesocket(AcceptSocket);
  102.                 break;
  103.             }
  104.             else
  105.             {
  106.                 printf_s("%d",iResult);
  107.                 printf_s("recv failed with error%d\n",WSAGetLastError());
  108.                 closesocket(AcceptSocket);
  109.                 closesocket(ServerSocket);
  110.                 WSACleanup();
  111.                 return 1;
  112.             }
  114.         }
  117.     }
  118.     closesocket(ServerSocket);
  119.     closesocket(AcceptSocket);
  120.     WSACleanup();
  123.     return 0;
  127. }

评价

  • 优点：使用非常简单直接
  • 缺点：
    • 无法同时处理多个套接字
    • 程序会在等待io处卡死，程序效率低下

改进思路：

  1. 多线程并发处理多个io，即一个线程处理一个socket，
    • 问题：线程频繁创建，唤醒，睡眠。导致用户态内核态频繁切换。增大系统开销
    • 线程同步，条件竞争，需要研究锁问题
  2. 异步，非阻塞处理多个io
    • 这种情况下，程序仍然为单线程，但是对io处理上使用回调机制，捕获io条件满足时机达到一对多效果
    • 问题：确定网络事件发生、网络io消息，回调机制