Linux IO模式及 select、poll、epoll详解及源码（转）

原文：https://segmentfault.com/a/1190000003063859

我只摘取了其中的epoll代码示例，服务端代码

#define IPADDRESS   "127.0.0.1"
#define PORT        8787
#define MAXSIZE     1024
#define LISTENQ     5
#define FDSIZE      1000
#define EPOLLEVENTS 100

listenfd = socket_bind(IPADDRESS,PORT);

struct epoll_event events[EPOLLEVENTS];

//创建一个描述符
epollfd = epoll_create(FDSIZE);

//添加监听描述符事件
add_event(epollfd,listenfd,EPOLLIN);

//循环等待
for ( ; ; ){
    //该函数返回已经准备好的描述符事件数目
    ret = epoll_wait(epollfd,events,EPOLLEVENTS,-);
    //处理接收到的连接
    handle_events(epollfd,events,ret,listenfd,buf);
}

//事件处理函数
static void handle_events(int epollfd,struct epoll_event *events,int num,int listenfd,char *buf)
{
     int i;
     int fd;
     //进行遍历;这里只要遍历已经准备好的io事件。num并不是当初epoll_create时的FDSIZE。
     for (i = ;i < num;i++)
     {
         fd = events[i].data.fd;
        //根据描述符的类型和事件类型进行处理
         if ((fd == listenfd) &&(events[i].events & EPOLLIN))
            handle_accpet(epollfd,listenfd);
         else if (events[i].events & EPOLLIN)
            do_read(epollfd,fd,buf);
         else if (events[i].events & EPOLLOUT)
            do_write(epollfd,fd,buf);
     }
}

//添加事件
static void add_event(int epollfd,int fd,int state){
    struct epoll_event ev;
    ev.events = state;
    ev.data.fd = fd;
    epoll_ctl(epollfd,EPOLL_CTL_ADD,fd,&ev);
}

//处理接收到的连接。将文件描述符添加到epoll监控队列
static void handle_accpet(int epollfd,int listenfd){
     int clifd;
     struct sockaddr_in cliaddr;
     socklen_t  cliaddrlen;
     clifd = accept(listenfd,(struct sockaddr*)&cliaddr,&cliaddrlen);
     if (clifd == -)
         perror("accpet error:");
     else {
         printf("accept a new client: %s:%d\n",inet_ntoa(cliaddr.sin_addr),cliaddr.sin_port);  //添加一个客户描述符和事件
         add_event(epollfd,clifd,EPOLLIN);
     }
}

//读处理
static void do_read(int epollfd,int fd,char *buf){
    int nread;
    nread = read(fd,buf,MAXSIZE);
    if (nread == -)     {
        perror("read error:");
        close(fd); //记住close fd
        delete_event(epollfd,fd,EPOLLIN); //删除监听
    }
    else if (nread == )     {
        fprintf(stderr,"client close.\n");
        close(fd); //记住close fd
        delete_event(epollfd,fd,EPOLLIN); //删除监听
    }
    else {
        printf("read message is : %s",buf);
        //修改描述符对应的事件，由读改为写
        modify_event(epollfd,fd,EPOLLOUT);
    }
}

//写处理
static void do_write(int epollfd,int fd,char *buf) {
    int nwrite;
    nwrite = write(fd,buf,strlen(buf));
    if (nwrite == -){
        perror("write error:");
        close(fd);   //记住close fd
        delete_event(epollfd,fd,EPOLLOUT);  //删除监听
    }else{
        modify_event(epollfd,fd,EPOLLIN);
    }
    memset(buf,,MAXSIZE);
}

//删除事件
static void delete_event(int epollfd,int fd,int state) {
    struct epoll_event ev;
    ev.events = state;
    ev.data.fd = fd;
    epoll_ctl(epollfd,EPOLL_CTL_DEL,fd,&ev);
}

//修改事件
static void modify_event(int epollfd,int fd,int state){
    struct epoll_event ev;
    ev.events = state;
    ev.data.fd = fd;
    epoll_ctl(epollfd,EPOLL_CTL_MOD,fd,&ev);
}

//注：另外一端我就省了