linux编程---IO复用---select

来源：互联网发布：多处理器编程的艺术编辑：程序博客网时间：2024/05/22 05:08

与多进程和多线程技术相比，I/O多路复用技术的最大优势是系统开销小，系统不必创建进程/线程，

也不必维护这些进程/线程，从而大大减小了系统的开销。

/* 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);

//将一个给定的文件描述符从集合中删除
void FD_CLR(int fd, fd_set *set);

// 检查集合中指定的文件描述符是否可以读写
int FD_ISSET(int fd, fd_set *set);

//将一个给定的文件描述符加入集合之中
void FD_SET(int fd, fd_set *set);

//清空集合
void FD_ZERO(fd_set *set);

实例如下

用select实现多客户接入服务器

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

#define MAXBUF 512
#define BACKLGO 10

int conn_amount;
int fd_cli[BACKLGO];

void showclient()
{
    int i;
    printf("client amount: %d\n", conn_amount);
    for (i = 0; i < BACKLGO; i++) {
        printf("[%d]:clifd[%d]\t", i, fd_cli[i]);
    }
    printf("\n\n");
}

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


   int serverfd,clifd,i;
   socklen_t len;
   struct sockaddr_in serveraddr,cliaddr;
   unsigned int serverport,lisnum;
   char buf[MAXBUF+1];
   fd_set rfds;
   struct timeval tv;
   int ret,maxfd = -1;

   serverport = 4332;
   lisnum = 5;

   socklen_t clilen = sizeof(struct sockaddr);
   if((serverfd = socket(AF_INET,SOCK_STREAM,0)) == -1)
   {
       perror("socket");
       exit(-1);
   }
   bzero(&serveraddr,sizeof(serveraddr));
   serveraddr.sin_family = AF_INET;
   serveraddr.sin_port = htons(serverport);
   serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);

   if(bind(serverfd,(struct sockaddr*)&serveraddr,sizeof(struct sockaddr)) < 0)
   {
       perror("bind");
       exit(-1);
   }

   if(listen(serverfd,lisnum) < 0)
   {
       perror("listen");
       exit(-1);
   }
   for(i = 0;i<BACKLGO;i++)
       fd_cli[i] = 0;

   maxfd = serverfd;

   while(1)
   {

       FD_ZERO(&rfds);
       FD_SET(serverfd,&rfds);
       FD_SET(0,&rfds);

       tv.tv_sec = 30;
       tv.tv_usec = 0;

       for(i = 0;i<BACKLGO;i++)
       {
           if(fd_cli[i] != 0)
           {
               FD_SET(fd_cli[i],&rfds);
           }
       }


       ret = select(maxfd + 1,&rfds,NULL,NULL,&tv);
       if(ret == -1)
       {
           perror("select");
           exit(-1);
       }
       else if(ret == 0)
       {
           continue;
       }
   else {
       for(i = 0; i< conn_amount;i++)
       {
           if(FD_ISSET(fd_cli[i],&rfds))
           {
               ret = recv(fd_cli[i],buf,sizeof(buf),0);
               char str[] = "hello client";
               send(fd_cli[i],str,sizeof(str)+1,0);

               if(ret <= 0)
               {
                   printf("client fd[%d] close\n",fd_cli[i]);
                   close(fd_cli[i]);
                   FD_CLR(fd_cli[i],&rfds);
                   fd_cli[i] = 0;
               }
               else
               {
                   if(ret < MAXBUF)
                       memset(&buf[ret],'\0',1);
                       printf("client fd [%d] send : [%s]\n",fd_cli[i],buf);
               }
           }
       }
       if(FD_ISSET(serverfd,&rfds))
       {
           clifd = accept(serverfd,(struct sockaddr*)&cliaddr,&clilen);
           if(clifd <= 0)
           {
               perror("accept");
               continue;
           }
           if(conn_amount < BACKLGO)
           {
               fd_cli[conn_amount++] = clifd;
               printf("new client connect fd:[%d] conn_amount:[%d],ip:[%s],port:[%d]\n",fd_cli[i],conn_amount,inet_ntoa(cliaddr.sin_addr),ntohs(cliaddr.sin_port));
               if(clifd > maxfd);
               maxfd = clifd;
           }
           else
           {
               printf("max connections,exit\n");
               send(clifd,"sorry",6,0);
               close(clifd);
               break;
           }
       }
       if(FD_ISSET(0,&rfds))
       {
           bzero(buf,MAXBUF + 1);
           fgets(buf,MAXBUF,stdin);
           if(!strncasecmp(buf,"quit",4))
           {
               printf("i will quit!\n");
               break;
           }
           for(i = 0;i < conn_amount;i++)
           {
               len = send(fd_cli[i],buf,strlen(buf)-1,0);
               if(len > 0)
                   printf("server send successful,%d bytes\n",len);
               else
               {
                   printf("send failed\n");
                   break;
               }
           }
       }
   }
       showclient();
   }

   for(i = 0;i < BACKLGO;i++)
   {
       if(fd_cli[i] != 0)
       {
           close(fd_cli[i]);
       }
   }
   close(serverfd);
   return 0;
}

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