2. epoll 实现回显服务器

代码

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdlib.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <errno.h>
#include <string.h>
#include <ctype.h>
#include <sys/epoll.h>
int main()
{
    int lfd = socket(AF_INET, SOCK_STREAM, 0);
    if (lfd == -1)
    {
        perror("socket error");
        exit(1);
    }
    //设置端口复用
    int opt = 1;
    setsockopt(lfd, SOL_SOCKET, SO_REUSEADDR, (const void *)&opt, sizeof(opt));
    struct sockaddr_in serv_addr;
    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(9317);
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    int ret = bind(lfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr));
    if (ret == -1)
    {
        perror("bind error");
        exit(1);
    }
    ret = listen(lfd, 64);
    if (ret == -1)
    {
        perror("listen error");
        exit(1);
    }
    struct sockaddr_in client_addr;
    socklen_t cli_addr_len = sizeof(struct sockaddr_in);
    //
    struct epoll_event events[2000];
    // 创建epoll实例
    int epfd = epoll_create(2000);
    //把监听事件挂到epoll红黑树上
    struct epoll_event event_l;
    event_l.events = EPOLLIN;
    event_l.data.fd = lfd;
    if ((epoll_ctl(epfd, EPOLL_CTL_ADD, lfd, &event_l)) < 0)
    {
        fprintf(stderr, "epoll ctl error: %s\n", strerror(errno));
        exit(1);
    }
    while (1)
    {
        // 有事件发送的epoll_event结构体会复制到events上，ret为事件总数
        int ret = epoll_wait(epfd, events, sizeof(events) / sizeof(events[0]), -1);
        if (ret < 0)
        {
            fprintf(stderr, "epoll wait error: %s\n", strerror(errno));
            exit(1);
        }
        int k;
        for (k = 0; k < ret; k++)
        {
            // 读事件
            if (events[k].events & EPOLLIN)
            {
                // tfd: this fd
                int tfd = events[k].data.fd;
                if (tfd == lfd)
                {
                    // 处理监听套接字的事件
                    int cfd = accept(lfd, (struct sockaddr *)&client_addr, &cli_addr_len);
                    if (cfd < 0)
                    {
                        fprintf(stderr, "accept error: %s\n", strerror(errno));
                    }
                    // 把客户端fd挂到epoll红黑树上
                    struct epoll_event tmp;
                    tmp.events = EPOLLIN;
                    tmp.data.fd = cfd;
                    if ((epoll_ctl(epfd, EPOLL_CTL_ADD, cfd, &tmp)) < 0)
                    {
                        fprintf(stderr, "epoll ctl error: %s\n", strerror(errno));
                        exit(1);
                    }
                }
                else
                {
                    // 客户端fd的事件
                    char buff[1024];
                    int rec_len, i;
                    if ((rec_len = recv(tfd, buff, sizeof(buff), 0)) < 0)
                    {
                        fprintf(stderr, "read error: %s\n", strerror(errno));
                        exit(1);
                    }
                    else if (rec_len == 0)
                    {
                        // 客户端关闭连接
                        if ((epoll_ctl(epfd, EPOLL_CTL_DEL, tfd, NULL)) < 0)
                        {
                            fprintf(stderr, "epoll ctl error: %s\n", strerror(errno));
                            exit(1);
                        }
                        close(tfd);
                    }
                    else
                    {
                        printf("%s", buff);
                        for (i = 0; i < rec_len; ++i)
                        {
                            buff[i] = toupper(buff[i]);
                        }
                        send(tfd, buff, rec_len, 0);
                    }
                }
            }
        }
    }
    close(epfd);
    close(lfd);
    return 0;
}

epoll的一点小问题

如果某个fd被关闭，并且这次关闭是真正地释放了资源，而不是减少引用技术，那么这个fd会自动从eopll中删除，这时再调用epoll_ctl(EPOLL_CTL_DEL)可能会报错。

   Q6  Will closing a file descriptor cause it  to  be  removed  from  all<br />           epoll sets automatically?

   A6  Yes,  but  be aware of the following point.  A file descriptor is a<br />           reference to an open file description (see  [open(2)](http://man.he.net/man2/open)).   Whenever  a<br />           descriptor  is duplicated via [dup(2)](http://man.he.net/man2/dup), [dup2(2)](http://man.he.net/man2/dup2), [fcntl(2)](http://man.he.net/man2/fcntl) F_DUPFD, or<br />           [fork(2)](http://man.he.net/man2/fork), a new file descriptor referring  to  the  same  open  file<br />           description  is  created.   An  open  file description continues to<br />           exist until all file descriptors referring to it have been  closed.<br />           A  file  descriptor is removed from an epoll set only after all the<br />           file descriptors referring to the underlying open file  description<br />           have been closed (or before if the descriptor is explicitly removed<br />           using [epoll_ctl(2)](http://man.he.net/man2/epoll_ctl) EPOLL_CTL_DEL).  This means that  even  after  a<br />           file  descriptor  that  is  part  of  an epoll set has been closed,<br />           events may be reported for  that  file  descriptor  if  other  file<br />           descriptors  referring  to  the  same  underlying  file description<br />           remain open.