linux下多路复用模型之Select模型

 

Linux关于并发网络分为Apache模型（Process per Connection (进程连接) ） 和TPC ， 还有select模型，以及poll模型（一般是Epoll模型）

 Select模型极其作用：这文章讲述的很好，没必要重述已有的东西，就直接给链接

          http://blog.csdn.net/turkeyzhou/article/details/8609360

        我的理解：

/* According to POSIX.1-2001 */
#include <sys/select.h>

/* According to earlier standards */
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>

int select(int nfds, fd_set *readfds, fd_set *writefds,
fd_set *exceptfds, struct timeval *timeout);

void FD_CLR(int fd, fd_set *set);
int FD_ISSET(int fd, fd_set *set);
void FD_SET(int fd, fd_set *set);
void FD_ZERO(fd_set *set);

    对于

   int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
        第一个参数 nfds：  第n个文件id的编号   （linux下，一切皆文件）  需要注意的是： nfds = fd+1 (fd 为 FD_SET中的fd)
        第二个参数：  fd_set *readfds   读取文件编号，如果不需要读取的话 可以设置为NULL
        第三 ，四个参数：  同上
        第五个参数：为一个定义超时的结构体

       struct timeval {
               time_t         tv_sec;     /* seconds */
               suseconds_t    tv_usec;    /* microseconds */
           };

         该结构用来设定多少时间为超时 ,比如

struct timeval ss ;
   ss.tv_sec  =3;
   ss.tv_usec =0; 
//表示设定为3秒后为超时，select将会返回0

对于下面这几个函数：

    void FD_CLR(int fd, fd_set *set); 

      用来清除fd的fd_set  ,比如fd为5  ，则表示set集中所有设定等于5的fd_set 都将被清除

 int FD_ISSET(int fd, fd_set *set); 

     判断是否set 与fd是否绑定，如果没有绑定，则返回false，如果绑定了则返回True

void FD_SET(int fd, fd_set *set);

        将fd值 和set绑定 

void FD_ZERO(fd_set *set);

   将set集全部清除

 

简单的例子：

判断是否有数据输入，有则直接打印出来

#include<stdio.h>
#include<string.h>
#include<sys/select.h>
#include<unistd.h>
#include<sys/time.h>
#include<sys/types.h>
#define maxn 6
#define EXIT_FAILURE  -1
#define EXIT_SUCCESS   0

int main(int argc , char * argv []){

   fd_set mtfd ;
   int ffd =0;
   struct timeval  outtime ;
   int retval  ;
   char redbuf[maxn];

   FD_ZERO(&mtfd);
   FD_SET(ffd , &mtfd);

// wait up to 5.5 s
   outtime.tv_sec = 5 ;
   outtime.tv_usec = 500 ;
   retval = select(ffd+1 , &mtfd ,NULL , NULL , &outtime);
   if(-1 == retval )
   {
     printf("error happened ! %d \n" ,__LINE__ );
     return EXIT_FAILURE ;
   }
   else if(0 == retval ){
      printf(" timeout !!  %d \n" ,__LINE__ );
     return  EXIT_FAILURE ;
    }
   //means that is good !

     printf("retval  =  %d \n", retval);

    if( FD_ISSET(ffd , &mtfd) ){

        memset(redbuf ,0 , sizeof(redbuf));
        printf("reading ... !! ");
       // read(1 , redbuf ,sizeof(redbuf) ); //use the sys func
       fread(redbuf , sizeof(redbuf) ,ffd+1 , stdin );
}
    //  fwrite(redbuf ,strlen(redbuf) , 1 , stdout );  
   //  write(1 , redbuf , strlen(redbuf)); 
     printf("buf = %s    buf_len = %d \n" , redbuf , strlen(redbuf));

    return EXIT_SUCCESS ;
}

makefile文件：

    

.SUFFIXES: .o.c
CC =gcc
SRC = Se_keyboard.c
OBJ = $(SRC: .c =.o)
BIN = Se_keyboard


.PHONY: start
start:  $(OBJ)
        $(CC) -o $(BIN) $(OBJ)
.o.c: $(SRC)
        $(CC) -g -Wall $@ -c  $<
.PHONY: clean
clean:
        rm -f $(OBJ)                    

 

 

  虽然知道这么多，但是还是觉得Select并没有什么作用。

   Select一般是和Socket搭配使用，相当于线程池的效果，但是线程池有缺点，详情看这儿：

       http://blog.csdn.net/tianmohust/article/details/6677985

       http://blog.csdn.net/xifeijian/article/details/17385831

  关于Select的原理图：

      首先来看下一对一的socket的c/s模式

      

 关于socket的一对一的详解

 http://www.cnblogs.com/gongxijun/p/4592864.html  

 看完这个之后，我们现在可以来看看这个图：

     

下面为举例：  

          服务器创建一个socket并bind绑定一个本机地址和设定一个端口，然后进入listen监听状态。采用select模型而非传统apache模型（ppc）或者tpc模型 。 不过Select模型就是有这样一个特点

  一般我们default默认的SOMAXCONN为128 当然我们可以另外取一个设定（下面我们设定的是2048）作为最大连接数，虽然可以设置更大，但是缺点是，select模型是一个轮询模式，就是每一个都需要遍历一边所有的链接的fd

  查看是否在fd_set集合中，这样，当SOMAXCONN取值非常大时，对于每一个客户端，访问时间都会延迟一点点，这样就是效率不是特别高！

 下面是一个简单的多路复用的网络并发Select模型

   

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<unistd.h>
#include<netinet/in.h>
#include<netinet/ip.h>
#include<sys/socket.h>
#include<sys/types.h>
#include<sys/time.h>
#include<arpa/inet.h>
#include<sys/select.h>
#include<assert.h>

#ifndef  EXIT_SUCCESS
#define EXIT_SUCCESS 0
#endif

#ifndef  EXIT_FAILURE
#define EXIT_FAILURE -1
#endif

#define Max_connect 2048    //usually is SOMAXCONN =128 ,can be change

#define maxn 1024
#define Port 5567
#define Ser_addr "192.168.132.128"

#define ERROR_EXIT( inf ) \
  do{    \
     perror( inf );  \
     printf("it happened in %d \n", __LINE__); \
     exit(-1); \
  }while(0);

#define  Waring( inf ) \
do{    \
     perror( inf );  \
     printf("it happened in %d \n", __LINE__); \
  }while(0);


int fds[Max_connect];
int cnt = 1;

void
print (int fd, const char *str)
{
  assert (str != NULL);
  printf ("the fd is %d \n", fd);
  puts (str);
}

int
main (int argv, char *argc[])
{

  int ser_sfd = -1, i;
  struct sockaddr_in ser_addr;
  struct sockaddr_in client_addr;
  int setfd = 0, optval, maxsockfd;

  char rebuf[maxn], wbuf[maxn];

  // build a socket with ipv4 ans tcp 

  if ((ser_sfd = socket (AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
    ERROR_EXIT ("socket...!");

  // set the type socket
  /*
     level ={ SOL_SOCKET ,IPPROTO_TCP}
     setsockopt is to cancle the jiangsi process
   */

  printf ("ser_sfd = %d  \n", ser_sfd);
  if (setsockopt (ser_sfd, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof (optval))
      < 0)
    ERROR_EXIT ("setsockopt...!");

  memset (&client_addr, 0, sizeof (client_addr));
  memset (&ser_addr, 0, sizeof (ser_addr));
  ser_addr.sin_family = AF_INET;
  ser_addr.sin_port = htons (Port);
  ser_addr.sin_addr.s_addr = htonl (INADDR_ANY);

  if (bind (ser_sfd, (struct sockaddr *) &ser_addr, sizeof (ser_addr)) < 0)
    ERROR_EXIT ("bind..!");

  if (listen (ser_sfd, Max_connect) < 0)
    ERROR_EXIT ("listen...!");

  //user the select moduel
  memset (fds, 0, sizeof (fds));
  fd_set fdset, wfd;
  maxsockfd = ser_sfd;        //max socket fd

  struct timeval tout;

  tout.tv_sec = 15;
  tout.tv_usec = 0;


  while (1)
    {

      FD_ZERO (&fdset);        //clear  
      //FD_ZERO (&wfd);

      FD_SET (ser_sfd, &fdset);    //bind
      //FD_SET (ser_sfd, &wfd);

      struct timeval tout;

      tout.tv_sec = 15;
      tout.tv_usec = 0;


      for (i = 0; i < cnt; i++)
    {
      if (fds[i] != 0)
        FD_SET (fds[i], &fdset);
    }

      int tag = select (maxsockfd + 1, &fdset, NULL, NULL, &tout);

      if (tag == 0)
    {
      Waring ("select wait timeout !");
      continue;
    }
      else if (tag == -1)
    ERROR_EXIT ("Error select ...!");

      //lunxun select
      for (i = 0; i < cnt; i++)
    {

      if (FD_ISSET (fds[i], &fdset))
        {

          int len = recv (fds[i], rebuf, sizeof (rebuf), 0);
          if (len <= 0)
        {

          printf ("%d: \n", fds[i]);
          close (fds[i]);
          FD_CLR (fds[i], &fdset);
          Waring ("client is closed !");
          continue;
        }

          printf ("the client_ip : %s\n",
              inet_ntoa (client_addr.sin_addr));

          print (fds[i], rebuf);

          send (fds[i], rebuf, sizeof (rebuf), 0);    //hui she
          memset (rebuf, 0, sizeof (rebuf));
        }
    }
      //if have a new connect happened
      //  memset(&client_addr , 0 ,sizeof(client_addr)); 
      if (FD_ISSET (ser_sfd, &fdset))
    {
      // memset(&client_addr , 0 ,sizeof(client_addr));
      int acplen = sizeof (client_addr);
      int acp = accept (ser_sfd, (struct sockaddr *) &client_addr,
                &acplen);

      printf ("accept return acp=%d \n", acp);

      if (acp < 0)
        {

          Waring ("waring accept acp<=0!");
          continue;
        }
      //add to arr
      if (cnt < maxn)
        fds[cnt++] = acp;
      else
        {
          ERROR_EXIT ("cnt>maxn");
        }
      if (acp > maxsockfd)
        maxsockfd = acp;
    }
    }

  for (i = 0; i < cnt; i++)
    {
      close (fds[i]);
    }

  return EXIT_SUCCESS;
}

makefile文件：
  

.SUFFIXES: .o.c 
CC =gcc
SRC =  server.c
OBJ = $(SRC: .c =.o) 
BIN = Sez_Server


.PHONY: start
start:  $(OBJ)
    $(CC) -o $(BIN) $(OBJ)
.o.c: $(SRC)
    $(CC) -g -Wall $@ -c  $<
.PHONY: clean
clean:
    rm -f $(OBJ)

客户端：

    

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<sys/socket.h>
#include<sys/types.h>
#include<assert.h>
#include<unistd.h>
#ifndef EXIT_FAILURE
#define EXIT_FAILURE  -1    //exit failure
#endif
#ifndef EXIT_SUCCESS
#define EXIT_SUCCESS   0    // exit sucessful
#endif

#define Port 5567
#define IPADDR  "192.168.132.128"
#define maxn 1024

#define ERROR_EXIT( inf ) \
 do{  \
   perror( inf ); \
   printf("it's happened in %d \n",__LINE__); \
   }while(0) ;


 //use the function to connect the server !!


int
main (int argv, char *argc[])
{

  int sfd = -1;
  char rbuf[maxn], wbuf[maxn];
  // int sfd=-1 ; //socket_fd
  int confd = -1;        //connect_fd
  struct sockaddr_in soaddr;
  if ((sfd = socket (AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
    {
      ERROR_EXIT ("socket");
      return EXIT_FAILURE;
    }

  //memset  a struct    
  memset (&soaddr, 0, sizeof (soaddr));

  //int the struct sockaddr_in

  soaddr.sin_family = AF_INET;
  soaddr.sin_port = htons (Port);
  soaddr.sin_addr.s_addr = inet_addr (IPADDR);

  if ((confd =
       connect (sfd, (struct sockadrr *) &soaddr, sizeof (soaddr))) < 0)
    {
      ERROR_EXIT ("connect");
      return EXIT_FAILURE;
    }

  printf ("connect is sucessful !\n");

  while (fgets (wbuf, sizeof (rbuf), stdin) != NULL)
    {
      write (sfd, wbuf, strlen (wbuf));
      read (sfd, rbuf, sizeof (rbuf));
      fputs (rbuf, stdout);
    }

  close (sfd);
  close (confd);
  return EXIT_SUCCESS;
}

makefile文件：

1.     

   .SUFFIXES: .o.c 
   CC =gcc
   SRC = client.c
   OBJ = $(SRC: .c =.o) 
   BIN = Se_client
   
   
   .PHONY: start
   start:  $(OBJ)
       $(CC) -o $(BIN) $(OBJ)
   .o.c: $(SRC)
       $(CC) -g -Wall $@ -c  $<
   .PHONY: clean
   clean:
       rm -f $(OBJ)

   效果图：

2.