Linux网络编程select模型的实现

来源：互联网发布：怎么淘宝卖二手书编辑：程序博客网时间：2024/06/06 02:11

简单的使用linux下的select模型实现了一个http的server

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <errno.h>
#include <netinet/in.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <stdlib.h>

#define LISTENQ 5
#define OPEN_MAX 1024
#define SERV_PORT 10088
#define MAX_LINE 1024
#define INFTIM -1

#define MAXEVENTS 1000

char szHtmlBuf[] = "HTTP/1.1 200 OK\r\n"
"Date: Sat, 05 Jan 2013 03:13:29 GMT\r\n"
"Vary: Accept-Encoding\r\n"
"Content-Type: text/html; charset=gb2312\r\n"
"Accept-Ranges: bytes\r\n"
"Content-Length: 57\r\n"
"\r\n"
"<html> <head>欢迎光临</head> <body>屌丝逆袭季</body></html>";

fd_set fds;

void echo_srv(int clientFd)
{
//处理用户请求数据
char line[MAX_LINE];
printf( "开始读取数据");
int n = read(clientFd, line, sizeof(line));
if(n < 0)
{
//#define ECONNRESET 104 /* Connection reset by peer */
if(errno == ECONNRESET)
{
close(clientFd);
FD_CLR(clientFd, &fds);
printf("异常退出\n");
}
else
{
printf("网络异常");
exit(-1);
}
}
else if(n == 0)
{
close(clientFd);
FD_CLR(clientFd, &fds);
printf("正常退出\n");
}
else
{
line[n] = 0;
printf("接收到数据:%s\n", line);

write(clientFd, szHtmlBuf, sizeof(szHtmlBuf));
}
}

int main()
{
struct sockaddr_in cliaddr, servaddr;
int listenFd = socket(AF_INET, SOCK_STREAM, 0);
if( listenFd < 0)
{
printf("socket函数执行失败");
return 1;
}

servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
//inet_aton('10.132.10.64', &(servaddr.sin_addr));
//servaddr.sin_addr.s_addr = inet_addr("10.132.10.64");
servaddr.sin_port = htons(SERV_PORT);
if(bind(listenFd, (struct sockaddr*)&servaddr, sizeof(servaddr)) < 0)
{
printf("bind函数执行失败");
return 1;
}

if(listen(listenFd, LISTENQ) < 0)
{
printf("listen函数执行失败");
return 1;
}
printf("listen函数执行成功\n");

//select 部分

int maxfd;
FD_ZERO(&fds);

do{
FD_SET(listenFd, &fds);
maxfd = listenFd + 1;
int nRead = 0;
if( (nRead = select(maxfd + 1, &fds, NULL, NULL, NULL)) < 0)
{
printf("select 失败\n");
exit(-1);
}
printf("select find data Change\n");
for(int i = 0; i <= maxfd && nRead > 0; i++)
{
if(!FD_ISSET(i, &fds))
{
continue;
}
--nRead;
if(i == listenFd)
{
socklen_t clilen = sizeof(cliaddr);
int connfd = accept(listenFd, (struct sockaddr*)&cliaddr, &clilen);
if(connfd < 0)
{
if ((errno != EAGAIN) && (errno != EWOULDBLOCK))
{
printf( "fail to accept new client \n");
continue;
}
}
printf("Ip: %s 到此一游\n", inet_ntoa(cliaddr.sin_addr));
FD_SET(connfd, &fds);
maxfd = (connfd > maxfd ? connfd : maxfd);
}
else
{
echo_srv(i);
}
}

}while(true);

return 0;
}

直接用浏览器进行测试即可：http://服务器Ip地址:10088

本篇文章来源于 Linux公社网站(www.linuxidc.com) 原文链接：http://www.linuxidc.com/Linux/2014-01/94777.htm

在网络上看到太多关于select i/o用法，都不是非常的详细。

经过摸索，把我实现的例子张贴上来，供大家参考。

描述：

服务器：实现并发tcp服务器，最多允许64 个客户端连接。

客户端：与服务器建立tcp连接，发送数据给服务器。服务器接收数据。

服务器代码：（红色为我的代码）

// SelectServerDlg.h : header file
//

#if !defined(AFX_SELECTSERVERDLG_H__3D5E9C67_8737_4E23_9734_0F196495ED30__INCLUDED_)
#define AFX_SELECTSERVERDLG_H__3D5E9C67_8737_4E23_9734_0F196495ED30__INCLUDED_

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000

/////////////////////////////////////////////////////////////////////////////
// CSelectServerDlg dialog
UINT proc(LPVOID lParam);

class CSelectServerDlg : public CDialog
{
// Construction
public:
CSelectServerDlg(CWnd* pParent = NULL); // standard constructor
CWinThread *pThread;
BOOL bRun;

// Dialog Data
//{{AFX_DATA(CSelectServerDlg)
enum { IDD = IDD_SELECTSERVER_DIALOG };
// NOTE: the ClassWizard will add data members here
//}}AFX_DATA

// ClassWizard generated virtual function overrides
//{{AFX_VIRTUAL(CSelectServerDlg)
protected:
virtual void DoDataExchange(CDataExchange* pDX); // DDX/DDV support
//}}AFX_VIRTUAL

// Implementation
protected:
HICON m_hIcon;

// Generated message map functions
//{{AFX_MSG(CSelectServerDlg)
virtual BOOL OnInitDialog();
afx_msg void OnSysCommand(UINT nID, LPARAM lParam);
afx_msg void OnPaint();
afx_msg HCURSOR OnQueryDragIcon();
afx_msg void OnClose();
//}}AFX_MSG
DECLARE_MESSAGE_MAP()
};

//{{AFX_INSERT_LOCATION}}
// Microsoft Visual C++ will insert additional declarations immediately before the previous line.

#endif // !defined(AFX_SELECTSERVERDLG_H__3D5E9C67_8737_4E23_9734_0F196495ED30__INCLUDED_)

————————————————————————————————————————

//SelectServerDlg.cpp代码

BOOL CSelectServerDlg::OnInitDialog()
{
CDialog::OnInitDialog();

// Add "About..." menu item to system menu.

// IDM_ABOUTBOX must be in the system command range.
ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
ASSERT(IDM_ABOUTBOX < 0xF000);

CMenu* pSysMenu = GetSystemMenu(FALSE);
if (pSysMenu != NULL)
{
  CString strAboutMenu;
  strAboutMenu.LoadString(IDS_ABOUTBOX);
  if (!strAboutMenu.IsEmpty())
  {
   pSysMenu->AppendMenu(MF_SEPARATOR);
   pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
  }
}

// Set the icon for this dialog. The framework does this automatically
// when the application's main window is not a dialog
SetIcon(m_hIcon, TRUE);   // Set big icon
SetIcon(m_hIcon, FALSE);  // Set small icon

// TODO: Add extra initialization here
WSAData wsadata;
WORD wVersionRequest;
wVersionRequest=MAKEWORD(2,2);
if(WSAStartup(wVersionRequest,&wsadata)!=0)
  TRACE("没有DLL可用\n");
if(LOBYTE(wsadata.wVersion) != 2 || HIBYTE(wsadata.wVersion) != 2)
{
  AfxMessageBox("socket dll 启动失败");
  WSACleanup();
}
pThread = AfxBeginThread(proc, this);
return TRUE; // return TRUE unless you set the focus to a control
}

——————————————————————————————————————

//服务器线程

UINT proc(LPVOID lParam)
{
try{
  fd_set rset;
  CSelectServerDlg *pDlg = (CSelectServerDlg*)lParam;
  struct sockaddr_in seraddr,cliaddr;
  int client[FD_SETSIZE],listensock;
  FD_ZERO(&rset);
  seraddr.sin_addr.s_addr = inet_addr("192.168.1.24");
  seraddr.sin_family = AF_INET;
  seraddr.sin_port = htons(6500);
  memset(seraddr.sin_zero, 0, 8);
  listensock = socket(AF_INET, SOCK_STREAM, 0);
  TRACE("listen socket :%d\n", listensock);
  bind(listensock, (struct sockaddr *)&seraddr, sizeof(seraddr));
  listen(listensock, 20);
  for(int i = 0; i<FD_SETSIZE; i++)
   client[i] = -1;
  pDlg->bRun = TRUE;
  int nReady;
  struct timeval timeout;
  int isset;
  int err;
  int maxfd;
  int connfd;
  int clilen;
  maxfd = listensock;
  char buf[1024];
  int recvbytes = 0;
  memset(buf, 0, 1024);
  while(pDlg->bRun){
   Sleep(1);
   timeout.tv_sec = 0;
   timeout.tv_usec = 10;
   /*
   listen socket 加入fdset
   */
   FD_SET(listensock, &rset);
   for(int n = 0; n<FD_SETSIZE; n++)
   {
    if(client[n]>0){
     FD_SET(client[n], &rset);
     if(client[n] > maxfd)
      maxfd = client[n];
    }

   }

   nReady = select(maxfd+1, &rset, NULL, NULL, &timeout);
   if(nReady == 0)
    //TRACE("select fun time out\n");
    ;
   else if(nReady == -1)
   {
    TRACE("socket error\n");
    err = WSAGetLastError();
    switch(err)
    {
    case WSANOTINITIALISED:
     TRACE("WSANOTINITIALISED 未初始化\n");
     break;
    case WSAEFAULT:
     TRACE("WSAEFAULT\n");
     break;
    case WSAENETDOWN:
     TRACE("WSAENETDOWN\n");
     break;
    case WSAEINVAL:
     TRACE("WSAEINVAL\n");
     break;
    case WSAEINTR:
     TRACE("WSAEINTR\n");
     break;
    case WSAEINPROGRESS:
     TRACE("WSAEINPROGRESS\n");
     break;
    case WSAENOTSOCK:
     TRACE("WSAENOTSOCK\n");
     break;
    }
   }
   else
   {
    /*
    测试已经建立连接的socket
    */
    unsigned long ul = 1;
    for(int j = 0; j<FD_SETSIZE; j++)
    {
     if(client[j]>0)
     {
      memset(buf,0,1024);
      isset = FD_ISSET(client[j],&rset);
      if(isset)
      {
       //ioctlsocket(client[j], FIONBIO, &ul);
       recvbytes = recv(client[j], buf, 1024, NULL);
       if(recvbytes>0)
        TRACE("from socket: %d,接收字节数:%d,%s\n",client[j], recvbytes, buf);
       else if(recvbytes == 0)
       {
        closesocket(client[j]);
        TRACE("client socket :%d closed! \n",client[j]);
        client[j] = -1;
       }
      }
     }
    }
    /*
    测试是否有连接？
    */
    isset = FD_ISSET(listensock, &rset);
    FD_ZERO(&rset);
    if(isset)
    {
     TRACE("conncetion.... \n");
     clilen = sizeof(cliaddr);
     connfd = accept(listensock,(struct sockaddr *)&cliaddr, &clilen);
     TRACE("connection comes from ip:%d.%d.%d.%d\n",cliaddr.sin_addr.S_un.S_un_b.s_b1,
      cliaddr.sin_addr.S_un.S_un_b.s_b2,
      cliaddr.sin_addr.S_un.S_un_b.s_b3,
      cliaddr.sin_addr.S_un.S_un_b.s_b4);
     for(int s=0; s<FD_SETSIZE; s++){
      if(client[s]<0){
       client[s] = connfd;
       break;
      }
     }

     TRACE("con number：%d\n", s+1);
     TRACE("socket id:");
     for(int k = 0; k < FD_SETSIZE; k++)
     {
      if(client[k]>0)
       TRACE("%d,",client[k]);
     }
     TRACE("\n");
    }

   }
  }
}

catch (...) {
TRACE("exception.........!!\n");
}
return TRUE;
}

——————————————————————————————————

//客户端代码：

BOOL CTcpClientDlg::OnInitDialog()
{
CDialog::OnInitDialog();

// Add "About..." menu item to system menu.

// IDM_ABOUTBOX must be in the system command range.
ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
ASSERT(IDM_ABOUTBOX < 0xF000);

CMenu* pSysMenu = GetSystemMenu(FALSE);
if (pSysMenu != NULL)
{
  CString strAboutMenu;
  strAboutMenu.LoadString(IDS_ABOUTBOX);
  if (!strAboutMenu.IsEmpty())
  {
   pSysMenu->AppendMenu(MF_SEPARATOR);
   pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
  }
}

// Set the icon for this dialog. The framework does this automatically
// when the application's main window is not a dialog
SetIcon(m_hIcon, TRUE); // Set big icon
SetIcon(m_hIcon, FALSE); // Set small icon

// TODO: Add extra initialization here

WSAData wsadata;
WORD wVersionRequest;
wVersionRequest=MAKEWORD(2,2);
if(WSAStartup(wVersionRequest,&wsadata)!=0)
  TRACE("没有DLL可用\n");
if(LOBYTE(wsadata.wVersion)!=2||HIBYTE(wsadata.wVersion)!=2)
{
  AfxMessageBox("socket dll 启动失败");
  WSACleanup();
}
serveraddr.sin_family=AF_INET;
serveraddr.sin_port=htons(6500);
serveraddr.sin_addr.S_un.S_un_b.s_b1=192;
serveraddr.sin_addr.S_un.S_un_b.s_b2=168;
serveraddr.sin_addr.S_un.S_un_b.s_b3=1;
serveraddr.sin_addr.S_un.S_un_b.s_b4=24;
clientsocket=socket(AF_INET,SOCK_STREAM,0);
return TRUE; // return TRUE unless you set the focus to a control
}

void CTcpClientDlg::OnSend()
{
// TODO: Add your control notification handler code here
nResult=connect(clientsocket,(struct sockaddr *)&serveraddr,sizeof(serveraddr));
if(nResult != SOCKET_ERROR)
{
  TRACE("连接成功\n");
  char *szSend="123456789";
  nResult=sendto(clientsocket,szSend,9,0,(struct sockaddr*)&serveraddr,sizeof(serveraddr));
  if(nResult != SOCKET_ERROR)
  {
   TRACE("发送成功\n");
  }
}

}

void CTcpClientDlg::OnButton2()
{
// TODO: Add your control notification handler code here
closesocket(clientsocket);
}

void CTcpClientDlg::OnButton3()
{
// TODO: Add your control notification handler code here
char *szSend="123456789";
nResult=sendto(clientsocket,szSend,9,0,(struct sockaddr*)&serveraddr,sizeof(serveraddr));
if(nResult != SOCKET_ERROR)
{
TRACE("发送成功\n");
}
}

(完)

在很长的时间内，相比于Windows平台众多的选择，select模式都是linux平台下网络通信的不多选择之一(在epoll未出生之前)。这种模式在面对大量短连接的时候，比OCOT有高的效率，可以避免频繁的上下文切换。

select系统调用是用来让我们的程序监视多个文件描述符(file descriptor)的状态变化的。程序会停在select这里等待，直到遇到以下情况之一select会退出：

(1) 监控的句柄至少有一个发生变化，返回值大于1。

(2) 等待时间已到，返回值等于0。

(3) 收到信号退出，返回值小于0。

select操作的内部会在指定的时间内，不断的检测受控集合中的套接字是否可读，可写或有错误，在select返回时只保留发生状态变化的套接字。通过判断select的返回值，就可以了解该调用是否有文件描述符可读或是select调用退出等信息。

要想让程序运行，光有一个select的调用不是不够的，我们还需要一系列的配套数据结构和算法来帮助将套接字归类，判断是否有指定的套接字等等，结构体fd_set和宏FD_ZERO,FD_CLR,FD_SET,FD_ISSET等就是我们所需要的。通过定义一个fd_set的对象，例如可读集合，有相同需求的套接字都可以放置到这个对象中，可以通过FD_SET这个宏来完成，当然在这之间需要利用FD_ZERO将这个对象初始化。等完成了以上操作后，便会调用select查询是否有套接字可读。等待select完成后，如果有套接字可读，就可以利用FD_ISSET判断是否为监听套接字，转而执行accept操作。如果一个套接字已经关闭，就可以利用FD_CLR将其从fd_set对象中剔除。

服务器端源代码：

#include <iostream>
2

#include <sys/socket.h>
3

#include <sys/types.h>
4

#include <arpa/inet.h>
5

#include <sys/select.h>
6

#include <sys/ioctl.h>
7

using namespace std;
8

int main()
10

{
11

int server_sock = socket(AF_INET,SOCK_STREAM,0);
13

if(server_sock < 0)
14

{
15

cout << "create socket error" << endl;
16

return -1;
17

}
18

struct sockaddr_in server_addr;
20

memset(&server_addr,0,sizeof(server_addr));
21

server_addr.sin_family = AF_INET;
22

server_addr.sin_port = htons(5555);
23

server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
24

if(bind(server_sock,(struct sockaddr*)&server_addr,sizeof(server_addr)) < 0)
26

{
27

cout << "bind socket error" << endl;
28

close(server_sock);
29

return -1;
30

}
31

listen(server_sock,10);
33

fd_set read_set;
35

fd_set test_set;
36

FD_ZERO(&read_set);
37

FD_SET(server_sock,&read_set);
38

struct timeval tm;
40

tm.tv_sec = 5;
41

tm.tv_usec = 500;
42

while(true)
45

{
46

int nread = 0;
47

test_set = read_set;
48

int ret = select(FD_SETSIZE,&test_set,NULL,NULL,&tm);
49

if(ret < 0)
51

{
52

cout << "select error" << endl;
53

close(server_sock);
54

return -1;
55

}
56

else if(ret == 0)
57

{
58

//cout << "waitout" << endl;
59

continue;
60

}
61

else
62

{
63

for(int fd=0; fd<FD_SETSIZE; ++fd)
64

{
65

if(FD_ISSET(fd,&test_set))
66

{
67

//如果有新的连接到达
68

if(fd == server_sock)
69

{
70

int sock = accept(server_sock,NULL,NULL);
71

FD_SET(sock,&read_set);
72

}
73

else
74

{
75

ioctl(fd,FIONREAD,&nread);
76

if(nread == 0) //客户端已经关闭
78

{
79

close(fd);
80

FD_CLR(fd,&read_set);
81

cout << "client has removed " << fd << endl;
82

}
83

else
84

{
85

char buf[128];
86

recv(fd,buf,128,0);
87

cout << buf << endl;
88

send(fd,buf,strlen(buf)+1,0);
89

}
90

}
91

}
93

}
95

}
97

}
99

}
100

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