Linux15 select,poll,epoll

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。

1.select

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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

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#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

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#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

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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

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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

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