我写的小程序

WSARecv 投递缓冲区也要对齐？？？不然就10014!

玻璃小屋 — Tue, 06 May 2008 17:23:00 GMT

如果把下面代码中背景色为绿色部分的 int iAlign = 4; 其中的 4 改为1或2，WSARecv就会返回 10014 错误。看来WSARecv 的投递的缓冲区也是要求对齐的。。正是因为这个问题。。浪费了我一天的时间调试我的内存池代码。。5555555555

#include <stdio.h>
#include "winsock2.h"

#define DATA_BUFSIZE 4096

void main() {
  //-----------------------------------------
  // Declare and initialize variables
  WSABUF DataBuf;
  char buffer[DATA_BUFSIZE];
  DWORD EventTotal = 0,
    RecvBytes = 0,
    Flags = 0,
    BytesTransferred = 0,
    CallBack = 0;
  WSAEVENT EventArray[WSA_MAXIMUM_WAIT_EVENTS];
  WSAOVERLAPPED AcceptOverlapped;
  SOCKET ListenSocket, AcceptSocket;

  //-----------------------------------------
  // Initialize Winsock
  WSADATA wsaData;
  WSAStartup(MAKEWORD(2,2), &wsaData);

  //-----------------------------------------
  // Create a listening socket bound to a local
  // IP address and the port specified
  ListenSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
  u_short port = 27015;
  char* ip;
  sockaddr_in service;
  service.sin_family = AF_INET;
  service.sin_port = htons(port);
  hostent* thisHost;
  thisHost = gethostbyname("");
  ip = inet_ntoa (*(struct in_addr *)*thisHost->h_addr_list);

  service.sin_addr.s_addr = inet_addr(ip);

  //-----------------------------------------
  // Bind the listening socket to the local IP address
  // and port number
  bind(ListenSocket, (SOCKADDR *) &service, sizeof(SOCKADDR));

  //-----------------------------------------
  // Set the socket to listen for incoming
  // connection requests
  listen(ListenSocket, 1);
  printf("Listening ");

  //-----------------------------------------
  // Accept and incoming connection request
  AcceptSocket = accept(ListenSocket, NULL, NULL);
  printf("Client Accepted ");

  //-----------------------------------------
  // Create an event handle and setup an overlapped structure.
  EventArray[EventTotal] = WSACreateEvent();
  ZeroMemory(&AcceptOverlapped, sizeof(WSAOVERLAPPED));
  AcceptOverlapped.hEvent = EventArray[EventTotal];
  DataBuf.len = DATA_BUFSIZE;
  DataBuf.buf = buffer;
  EventTotal++;

  LPWSABUF lpwsaBuf;

  //int iAlign = 1;
  int iAlign = 4;

  lpwsaBuf = (LPWSABUF) ((new CHAR[sizeof(WSABUF) + iAlign]) + iAlign);//pOverlapBuff->GetWSABuffer();
  lpwsaBuf->buf = new CHAR[52];
  lpwsaBuf->len = 52;

  //-----------------------------------------
  // Call WSARecv to receive data into DataBuf on
  // the accepted socket in overlapped I/O mode
  if (WSARecv(AcceptSocket, lpwsaBuf, 1, &RecvBytes, &Flags, &AcceptOverlapped, NULL) == SOCKET_ERROR)
  {
      if (WSAGetLastError() != WSA_IO_PENDING)
      {
          printf("Error occured at WSARecv() %d ",WSAGetLastError());
          closesocket(AcceptSocket);
          return;
      }
  }

  //-----------------------------------------
  // Process overlapped receives on the socket
  while (1) {
    DWORD Index;

    //-----------------------------------------
    // Wait for the overlapped I/O call to complete
    Index = WSAWaitForMultipleEvents(EventTotal, EventArray, FALSE, WSA_INFINITE, FALSE);

    //-----------------------------------------
    // Reset the signaled event
    WSAResetEvent(EventArray[Index - WSA_WAIT_EVENT_0]);

    //-----------------------------------------
    // Determine the status of the overlapped event
    WSAGetOverlappedResult(AcceptSocket, &AcceptOverlapped, &BytesTransferred, FALSE, &Flags);

    //-----------------------------------------
    // If the connection has been closed, close the accepted socket
    if (BytesTransferred == 0) {
      printf("Closing Socket %d ", AcceptSocket);
      closesocket(AcceptSocket);
      WSACloseEvent(EventArray[Index - WSA_WAIT_EVENT_0]);
      return;
    }

    //-----------------------------------------
    // If data has been received, echo the received data
    // from DataBuf back to the client
    if (WSASend(AcceptSocket, &DataBuf, 1, &RecvBytes, Flags, &AcceptOverlapped, NULL) == SOCKET_ERROR)
      printf("WSASend() is busted ");

    //-----------------------------------------
    // Reset the changed flags and overlapped structure
    Flags = 0;
    ZeroMemory(&AcceptOverlapped, sizeof(WSAOVERLAPPED));

    AcceptOverlapped.hEvent = EventArray[Index - WSA_WAIT_EVENT_0];

    //-----------------------------------------
    // Reset the data buffer
    DataBuf.len = DATA_BUFSIZE;
    DataBuf.buf = buffer;
  }
}

结构对齐对结构成员的访问效率影响的测试。

玻璃小屋 — Fri, 02 May 2008 14:14:00 GMT

测试一下结构对齐对其成员访问效率的影响，程序中应该涉及到了对结构成员变量的读/写操作，测试应该是比较全面可信的。
测试结果表明，改变结构默认的对齐方式对其成员访问效率的影响是蛮大的。另外按CPU宽度来测试似乎与默认对齐方式的结果差不多，看来 #pragma pack(1)还是要慎用！！唉~~ 不过要是在 pack(1) 慎用的情况下，做socket 程序时。。。发送或接收数据的结构可怎么写？？用 pack(1) 定义socket的收/发数据结构用起来很方便啊。。可是如果为了效率而舍弃的啊？这些数据该规划用什么方式来访问呢？有比用 pack(1)来定义结构更方遍，更高效的方法吗？

#pragma pack(1)

class Test
{
public:
    char    a;
    int        b;
};

#pragma pack()

class Test1
{
public :
    char a;
    int b;
};

__declspec(align(32)) class S
{
public:
     char a;
     int b;
} ;

void main()
{

    for(int k = 0; k < 20; k++)
    {
        Test t;
        t.a = 0x33;
        t.b = 3;
        int j = 0;
        int g = 0;
        DWORD dTick = GetTickCount();
        for(int i = 0; i < 100000000; i++)
        {
            if(t.b == g)
            {
                j++;
            }

            t.b = i;
            g = j;
        }

        printf("Test0：%d %d %d ",__alignof(Test),sizeof(Test),GetTickCount() - dTick);

        Test1 t1;
        t1.a = 0x33;
        t1.b = 3;


        dTick = GetTickCount();
        for(int i = 0; i < 100000000; i++)
        {
            if(t1.b == g)
            {
                j++;
            }

            t1.b = i;
            g = j;
        }

        printf("Test1：%d %d %d ",__alignof(Test1),sizeof(Test1),GetTickCount() - dTick);

        S t2;
        t2.a = 0x33;
        t2.b = 3;

        dTick = GetTickCount();
        for(int i = 0; i < 100000000; i++)
        {
            if(t2.b == g)
            {
                j++;
            }

            t2.b = i;
            g = j;
        }

        printf("Test2：%d %d %d ",__alignof(S),sizeof(S),GetTickCount() - dTick);

    }
}

输出结果：

Test0：1        5       437
Test1：4        8       125
Test2：32       32      125