linux下用epoll实现的udp服务器例子,很精简和实用

#include <sys/socket.h>
#include <sys/epoll.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h> 
#include <errno.h> 
#include <stdlib.h>
#include <string.h>
#include <strings.h>

#define MAXLINE 10
#define OPEN_MAX 100
#define LISTENQ 20
#define SERV_PORT 5555
#define INFTIM 1000 
#define MAX_EVENT 10000

void setnonblocking(int sock)
{
    int opts;
    opts=fcntl(sock,F_GETFL);

    if(opts<0)

    {
        perror("fcntl(sock,GETFL)");
        exit(1);
    }

    opts = opts|O_NONBLOCK;
    if(fcntl(sock,F_SETFL,opts)<0)
    {
        perror("fcntl(sock,SETFL,opts)");
        exit(1);
    }    

}



int main()
{
    int i, maxi, listenfd, connfd, sockfd,epfd,nfds;
    int ret;
    ssize_t n;
    char line[MAXLINE];
    socklen_t clilen;
    char szAddr[256]="\0";

    //声明epoll_event结构体的变量,ev用于注册事件,数组用于回传要处理的事件

    struct epoll_event ev,events[20];

    //生成用epoll专用文件描述符

    epfd=epoll_create(256);printf("epoll_create(256) return %d\n", epfd);
    struct sockaddr_in clientaddr;  
    struct sockaddr_in serveraddr;  
    listenfd = socket(AF_INET, SOCK_DGRAM, 0);
    socklen_t addrlen = sizeof(clientaddr);

    //把socket设置为非阻塞方式   
    setnonblocking(listenfd);   
    //设置与要处理的事件相关的文件描述符 
    ev.data.fd=listenfd;
    //设置要处理的事件类型    
    ev.events=EPOLLIN|EPOLLET;  
    //注册epoll事件

    ret=epoll_ctl(epfd,EPOLL_CTL_ADD,listenfd,&ev);
    printf("epoll_ctl return %d\n",ret);
    bzero(&serveraddr, sizeof(serveraddr));
    serveraddr.sin_family = AF_INET;
    char *local_addr="127.0.0.1";

    inet_aton(local_addr,&(serveraddr.sin_addr));
    serveraddr.sin_addr.s_addr=inet_addr(local_addr);
    serveraddr.sin_port=htons(SERV_PORT);

    bind(listenfd,(struct sockaddr *)&serveraddr, sizeof(serveraddr));
    memset(line,0,MAXLINE);

    for ( ; ; ) 
    {
        //等待epoll事件的发生
        //nfds=epoll_wait(epfd,events,MAX_EVENT,-1);
        nfds=epoll_wait(epfd,events,MAX_EVENT,0);
        //处理所发生的所有事件      

        for(i=0;i<nfds;++i) 
        {
            if(events[i].events&EPOLLIN)                
            {
                if ( (sockfd = events[i].data.fd) < 0)
                    continue;

                if ((n = recvfrom(sockfd, line, MAXLINE,0,(sockaddr*)&clientaddr,&addrlen)) < 0)
                {
                    if (errno == ECONNRESET)
                    {
                        close(sockfd);                      
                        events[i].data.fd = -1;

                    } 
                    else 
                        printf("readline error\n");

                } else if (n == 0)
                {
                    perror("connfd=0\n");
                    close(sockfd);
                    events[i].data.fd = -1;
                }

                char* p = (char *)&clientaddr.sin_addr;
                sprintf(szAddr, "%d.%d.%d.%d", *p, *(p+1), *(p+2), *(p+3));

                printf("recv %s from ip:%s\n",line,szAddr);
                //设置用于写操作的文件描述符             
                ev.data.fd=sockfd;              
                //设置用于注测的写操作事件              
                ev.events=EPOLLOUT|EPOLLET;             
                //修改sockfd上要处理的事件为EPOLLOUT              
                epoll_ctl(epfd,EPOLL_CTL_MOD,sockfd,&ev);               
            }

            else if(events[i].events&EPOLLOUT)              
            {    
                if(events[i].data.fd == -1)
                    continue;

                sockfd = events[i].data.fd;             
                write(sockfd, line, n);
                printf("send %s\n",line);               
                //设置用于读操作的文件描述符             
                ev.data.fd=sockfd;              
                //设置用于注测的读操作事件          
                ev.events=EPOLLIN|EPOLLET;      
                char buf[256]="test";
                sendto(sockfd,buf,strlen(buf),0,(sockaddr*)&clientaddr,addrlen);
                //修改sockfd上要处理的事件为EPOLIN                
                epoll_ctl(epfd,EPOLL_CTL_MOD,sockfd,&ev);               
            }
          }
     }

}