1.select



selsect.c
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<string.h>
#include<assert.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#define MAXFD 10
void fds_add(int fds[],int fd)
{
int i=0;
for(;i<MAXFD;i++)
{
if(fds[i]==-1)
{
fds[i]=fd;
break;
}
}
}
void fds_del(int fds[],int fd)
{
int i=0;
for(;i<MAXFD;i++)
{
if(fds[i]==fd)
{
fds[i]=-1;
break;
}
}
}
int main()
{
int sockfd=socket(AF_INET,SOCK_STREAM,0);
assert(sockfd!=-1);
struct sockaddr_in saddr;
memset(&saddr,0,sizeof(saddr));
saddr.sin_family=AF_INET;
saddr.sin_port=htons(6000);
saddr.sin_addr.s_addr=inet_addr("127.0.0.1");
//int res=connect(sockfd,(struct sockaddr*)&saddr,sizeof(saddr));
int res =bind(sockfd,(struct sockaddr*)&saddr,sizeof(saddr));
assert(res!=-1);
listen(sockfd,5);
fd_set fdset;
int fds[MAXFD];//collect fd;
int i=0;
for(;i<MAXFD;i++)
{
fds[i]=-1;
}
fds_add(fds,sockfd);
while(1)
{
FD_ZERO(&fdset);
int maxfd=-1;
int i=0;
for(;i<MAXFD;i++)
{
if(fds[i]==-1)
{
continue;
}
FD_SET(fds[i],&fdset);
if(fds[i]>maxfd)
{
maxfd=fds[i];
}
}
struct timeval tv={5,0};
int n=select(maxfd+1,&fdset,NULL,NULL,&tv);
if(n==-1)
{
perror("select error!!");
}
else if(n==0)
{
printf("time out\n");
}
else
{
for(i=0;i<MAXFD;i++)
{
if(fds[i]==-1)
{
continue;
}
if(FD_ISSET(fds[i],&fdset))
{
if(fds[i]==sockfd)
{
//accept
struct sockaddr_in caddr;
int len =sizeof(caddr);
int c=accept(sockfd,(struct sockaddr*)&caddr,&len);
if(c<0)
{
continue;
}
printf("accept c=%d\n",c);
fds_add(fds,c);
}
else
{
//recv;
char buff[128]={0};
int res =recv(fds[i],buff,127,0);
if(res<=0)
{
close(fds[i]);
fds_del(fds,fds[i]);
printf("one client over!!\n");
}
else
{
printf("recv(%d)=%s\n",fds[i],buff);
send(fds[i],"ok",2,0);
}
}
}
}
}
}
}
2.poll


#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<string.h>
#include<assert.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<poll.h>
#define MAXFD 10
int creat_sockfd();
void fds_add(struct pollfd fds[],int fd)
{
int i=0;
for(;i<MAXFD;i++)
{
if(fds[i].fd==-1)
{
fds[i].fd=fd;
fds[i].events=POLLIN;
fds[i].revents=0;
break;
}
}
}
void fds_del(struct pollfd fds[],int fd)
{
int i=0;
for(;i<MAXFD;i++)
{
if(fds[i].fd==fd)
{
fds[i].fd=-1;
fds[i].events=0;
fds[i].revents=0;
break;
}
}
}
void fds_init(struct pollfd fds[])
{
int i=0;
for(;i<MAXFD;i++)
{
fds[i].fd=-1;
fds[i].events=0;
fds[i].revents=0;
}
}
int main()
{
int sockfd=creat_sockfd();
assert(sockfd!=-1);
struct pollfd fds[MAXFD];
fds_init(fds);
fds_add(fds,sockfd);
while(1)
{
int n=poll(fds,MAXFD,5000);//zu se;????????????
if(n==-1)
{
perror("poll error");
}
if(n==0)
{
printf("time out!!\n");
}
else
{
int i=0;
for(;i<MAXFD;i++)
{
if(fds[i].fd==-1)
{
continue;
}
if(fds[i].revents & POLLIN)
{
if(fds[i].fd==sockfd)
{
//accept
struct sockaddr_in caddr;
int len =sizeof(caddr);
int c=accept(sockfd,(struct sockaddr*)&caddr,&len);
if(c<0)
{
continue;
}
printf("accept c=%d\n",c);
fds_add(fds,c);
}
else
{
//recv
char buff[128]={0};
int res=recv(fds[i].fd,buff,127,0);
if(res<=0)
{
close(fds[i].fd);
fds_del(fds,fds[i].fd);
printf("one client over!!\n");
}
else
{
printf("recv(%d)=%s\n",fds[i].fd,buff);
send(fds[i].fd,"ok",2,0);
}
}
}
}
}
}
}
int creat_sockfd()
{
int sockfd=socket(AF_INET,SOCK_STREAM,0);
if(sockfd==-1)
{
return -1;
}
struct sockaddr_in saddr;
memset(&saddr,0,sizeof(saddr));
saddr.sin_family =AF_INET;
saddr.sin_port =htons(6000);
saddr.sin_addr.s_addr=inet_addr("127.0.0.1");
//saddr.sin_addr.s_addr=inet((struct sockaddr*)&saddr,sizeof(saddr));
int res=bind(sockfd,(struct sockaddr*)&saddr,sizeof(saddr));
assert(res!=-1);
listen(sockfd,20);
return sockfd;
}
3.epoll



#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<string.h>
#include<assert.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<sys/epoll.h>
#define MAXFD 10
int creat_sockfd();
void epoll_add(int epfd,int fd)
{
struct epoll_event ev;
ev.data.fd=fd;
ev.events=EPOLLIN;
if( epoll_ctl(epfd,EPOLL_CTL_ADD,fd,&ev)==-1)
{
perror("epoll error!!");
}
}
void epoll_del(int epfd,int fd)
{
if(epoll_ctl(epfd,EPOLL_CTL_DEL,fd,NULL)==-1)
{
perror("epoll_del error!!");
}
}
int main()
{
int sockfd=creat_sockfd();
assert(sockfd!=-1);
int epfd=epoll_create(MAXFD);
assert(epfd!=-1);
epoll_add(epfd,sockfd);
struct epoll_event events[MAXFD];//creat neihe event
while(1)
{
int n=epoll_wait(epfd,events,MAXFD,5000);
if(n==-1)
{
perror("epoll_wait error!!");
}
if(n==0)
{
printf("time out!!\n");
}
else
{
int i=0;
for(;i<n;i++)
{
int fd=events[i].data.fd;
if(events[i].events & EPOLLIN)
{
if(fd==sockfd)
{
//accept
struct sockaddr_in caddr;
int len =sizeof(caddr);
int c=accept(sockfd,(struct sockaddr*)&caddr,&len);
if(c<0)
{
continue;
}
printf("accept c=%d\n",c);
epoll_add(epfd,c);
}
else
{
//recv
char buff[128]={0};
int num=recv(fd,buff,127,0);
if(num==0)
{
epoll_del(epfd,fd);//xian yichu zai close
close(fd);
printf("one client over!!\n");
}
else
{
printf("buff(%d)=%s\n",fd,buff);
send(fd,"ok",2,0);
}
}
}
}
}
}
}
int creat_sockfd()
{
int sockfd=socket(AF_INET,SOCK_STREAM,0);
if(sockfd==-1)
{
return -1;
}
struct sockaddr_in saddr;
memset(&saddr,0,sizeof(saddr));
saddr.sin_family =AF_INET;
saddr.sin_port =htons(6000);
saddr.sin_addr.s_addr=inet_addr("127.0.0.1");
//saddr.sin_addr.s_addr=inet((struct sockaddr*)&saddr,sizeof(saddr));
int res=bind(sockfd,(struct sockaddr*)&saddr,sizeof(saddr));
assert(res!=-1);
listen(sockfd,20);
return sockfd;
}
4.epoll的两种工作模式

4.1LT模式
LT(没读完io提醒继续读,直到读完为止)默认反复提醒,返回次数为字符数
默认为LT模式
4.2ET模式
只能使用非阻塞模式(减少返回次数,只返回一次),fcntl开启高效模式:发一次数据才会提醒一次,只提醒一次,无论处理还是未处理完,只提醒一次。客户端一关,服务器就崩掉了,原因是:
4.2.1 代码实现
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<string.h>
#include<assert.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<sys/epoll.h>
#include<fcntl.h>
#define MAXFD 10
int creat_sockfd();
void setnonblock(int fd)
{
int oldfl=fcntl(fd,F_GETFL);
int newfl=oldfl| O_NONBLOCK;
if(fcntl(fd,F_SETFL,newfl)==-1)
{
perror("fcntl error");
}
}
void epoll_add(int epfd,int fd)
{
//开启ET模式
struct epoll_event ev;
ev.data.fd=fd;
ev.events=EPOLLIN;
ev.events|=EPOLLET;
if( epoll_ctl(epfd,EPOLL_CTL_ADD,fd,&ev)==-1)
{
perror("epoll error!!");
}
setnonblock(fd);//设置非阻塞
}
void epoll_del(int epfd,int fd)
{
if(epoll_ctl(epfd,EPOLL_CTL_DEL,fd,NULL)==-1)
{
perror("epoll_del error!!");
}
}
int main()
{
int sockfd=creat_sockfd();
assert(sockfd!=-1);
int epfd=epoll_create(MAXFD);
assert(epfd!=-1);
epoll_add(epfd,sockfd);
struct epoll_event events[MAXFD];//creat neihe event创建内核事件
while(1)
{
int n=epoll_wait(epfd,events,MAXFD,5000);//5s
if(n==-1)
{
perror("epoll_wait error!!");
}
if(n==0)
{
printf("time out!!\n");
}
else
{
int i=0;
for(;i<n;i++)
{
int fd=events[i].data.fd;
if(events[i].events & EPOLLIN)
{
if(fd==sockfd)
{
//accept
struct sockaddr_in caddr;
int len =sizeof(caddr);
int c=accept(sockfd,(struct sockaddr*)&caddr,&len);
if(c<0)
{
continue;
}
printf("accept c=%d\n",c);
epoll_add(epfd,c);
}
else
{
//recv
char buff[128]={0};
int num=recv(fd,buff,127,0);
if(num==0)
{
epoll_del(epfd,fd);//xian yichu zai close
close(fd);
printf("one client over!!\n");
break;
}
else if(num==-1)
{
send(fd,"ok",2,0);
break;
}
else
{
printf("buff(%d)=%s\n",fd,buff);
send(fd,"ok",2,0);
}
}
}
}
}
}
}
int creat_sockfd()
{
int sockfd=socket(AF_INET,SOCK_STREAM,0);
if(sockfd==-1)
{
return -1;
}
struct sockaddr_in saddr;
memset(&saddr,0,sizeof(saddr));
saddr.sin_family =AF_INET;
saddr.sin_port =htons(6000);
saddr.sin_addr.s_addr=inet_addr("127.0.0.1");
//saddr.sin_addr.s_addr=inet((struct sockaddr*)&saddr,sizeof(saddr));
int res=bind(sockfd,(struct sockaddr*)&saddr,sizeof(saddr));
assert(res!=-1);
listen(sockfd,20);
return sockfd;
}
4.2.3

4.2.4利用管道处理两种事件
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <assert.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <fcntl.h>
#include <signal.h>
#include <errno.h>
int pipefd[2];
#define MAXFD 10
int create_sockfd();
void epoll_add(int epfd, int fd)
{
struct epoll_event ev;
ev.data.fd = fd;
ev.events = EPOLLIN | EPOLLRDHUP;//读事件
if ( epoll_ctl(epfd,EPOLL_CTL_ADD,fd,&ev) == -1 )
{
perror("epoll_ctl error");
}
}
void epoll_del(int epfd, int fd)
{
if ( epoll_ctl(epfd,EPOLL_CTL_DEL,fd,NULL) == -1 )
{
perror("epoll_ctl del error");
}
}
void fun(int sig)
{
write(pipefd[1],&sig,sizeof(sig));
}
int main()
{
int sockfd = create_sockfd();
assert( sockfd != -1 );
pipe(pipefd);//创建管道
int epfd = epoll_create(MAXFD); //创建内核事件
assert( epfd != -1 );
epoll_add(epfd,sockfd);
epoll_add(epfd,pipefd[0]);//添加管道的读端
signal(SIGINT,fun);
struct epoll_event events[MAXFD];
int run = 1;
while( run )
{
int n = epoll_wait(epfd,events,MAXFD,5000);
if ( n == -1 )
{
if ( errno != EINTR )
{
perror("epoll_wait error");
}
}
else if ( n == 0 )
{
printf("time out\n");
}
else
{
int i = 0;
for( ;i < n; i++ )
{
int fd = events[i].data.fd;
if ( events[i].events & EPOLLRDHUP)
{
epoll_del(epfd,fd);
close(fd);
printf("one client hup over\n");
}
if ( events[i].events & EPOLLIN )
{
if ( fd == sockfd )
{
//accept
struct sockaddr_in caddr;
int len = sizeof(caddr);
int c = accept(sockfd,(struct sockaddr*)&caddr,&len);
if ( c < 0 )
{
continue;
}
printf("accept c=%d\n",c);
epoll_add(epfd,c);
}
else if ( fd == pipefd[0] )
{
int sig = 0;
read(pipefd[0],&sig,sizeof(sig));
printf("recv sig=%d\n",sig);
run = 0;
}
else
{
//recv
char buff[128] = {0};
int num = recv(fd,buff,127,0);
if ( num == 0 )
{
epoll_del(epfd,fd);
close(fd);
printf("one client over\n");
}
else
{
printf("buff(%d)=%s\n",fd,buff);
send(fd,"ok",2,0);
}
}
}
}
}
}
close(sockfd);
close(epfd);
printf("main over\n");
}
int create_sockfd()
{
int sockfd = socket(AF_INET,SOCK_STREAM,0);
if ( sockfd == -1 )
{
return -1;
}
struct sockaddr_in saddr;
memset(&saddr,0,sizeof(saddr));
saddr.sin_family = AF_INET;
saddr.sin_port = htons(6000);
saddr.sin_addr.s_addr = inet_addr("127.0.0.1");
int res = bind(sockfd,(struct sockaddr*)&saddr,sizeof(saddr));
if ( res == -1 )
{
return -1;
}
listen(sockfd,5);
return sockfd;
}
5.select,poll,epoll三种的区别



本文详细介绍了I/O多路复用技术中的select、poll和epoll三种方法,包括它们的工作原理、代码实现和应用场景。select和poll通过轮询多个文件描述符来检测其是否就绪,而epoll则提供了更高效的事件驱动模型,特别是ET模式下结合非阻塞IO,能显著提升服务器性能。
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