epoll return 如何得到正确的文件描述符

Question

我有两个 UDP 连接，我正在尝试添加它们以使用 epoll()。我正在看这个例子：

https://programmer.ink/think/epoll-for-linux-programming.html

我已经粘贴了下面的代码。

一开始他们创建了一个 epoll 事件以及一系列 epoll 事件：

struct epoll_event ev,events[20];

我不确定为什么两者都需要。

然后他们打电话给 epoll_wait():

nfds=epoll_wait(epfd,events,20,500);

并检索到套接字：

if(events[i].data.fd==listenfd)

但是，events 未填充在这三行之间。

那么events[i].data.fd是如何包含socket文件描述符的呢？

如果我们有一个epoll_event的数组，为什么要设置ev.data.fd=listenfd;，它有一个文件描述符数据成员？

struct epoll_event ev,events[20];
//Generate epoll-specific file descriptors for processing accept s

epfd=epoll_create(256);
struct sockaddr_in clientaddr;
struct sockaddr_in serveraddr;
listenfd = socket(AF_INET, SOCK_STREAM, 0);
//Set socket to non-blocking

//setnonblocking(listenfd);

//Set the file descriptor associated with the event to be processed

ev.data.fd=listenfd;
//Set the type of event to process

ev.events=EPOLLIN|EPOLLET;
//ev.events=EPOLLIN;

//Register epoll events

epoll_ctl(epfd,EPOLL_CTL_ADD,listenfd,&ev);
bzero(&serveraddr, sizeof(serveraddr));
serveraddr.sin_family = AF_INET;
char *local_addr="127.0.0.1";
inet_aton(local_addr,&(serveraddr.sin_addr));//htons(portnumber);

serveraddr.sin_port=htons(portnumber);
bind(listenfd,(struct sockaddr *)&serveraddr, sizeof(serveraddr));
listen(listenfd, LISTENQ);
maxi = 0;
for ( ; ; ) {
    //Waiting for the epoll event to occur

    nfds=epoll_wait(epfd,events,20,500);
    //Handle all events that occur

    for(i=0;i<nfds;++i)
    {
        if(events[i].data.fd==listenfd)//If a new SOCKET user is detected to be connected to a bound SOCKET port, establish a new connection.

        {
            connfd = accept(listenfd,(struct sockaddr *)&clientaddr, &clilen);
            if(connfd<0){
                perror("connfd<0");
                exit(1);
            }
            //setnonblocking(connfd);

            char *str = inet_ntoa(clientaddr.sin_addr);
            printf("accapt a connection from\n ");
            //Setting file descriptors for read operations

            ev.data.fd=connfd;
            //Set Read Action Events for Annotation

            ev.events=EPOLLIN|EPOLLET;
            //ev.events=EPOLLIN;

            //Register ev

            epoll_ctl(epfd,EPOLL_CTL_ADD,connfd,&ev);
        }
        else if(events[i].events&EPOLLIN)//If the user is already connected and receives data, read in.

        {
            printf("EPOLLIN\n");
            if ( (sockfd = events[i].data.fd) < 0)
                continue;
            if ( (n = read(sockfd, line, MAXLINE)) < 0) {
                if (errno == ECONNRESET) {
                    close(sockfd);
                    events[i].data.fd = -1;
                } else
                    printf("readline error\n");
            } else if (n == 0) {
                close(sockfd);
                events[i].data.fd = -1;
            }
            if(n<MAXLINE-2)
                line[n] = '[=11=]';

            //Setting file descriptors for write operations

            ev.data.fd=sockfd;
            //Set Write Action Events for Annotation

            ev.events=EPOLLOUT|EPOLLET;
            //Modify the event to be handled on sockfd to EPOLLOUT

            //epoll_ctl(epfd,EPOLL_CTL_MOD,sockfd,&ev);

        }
        else if(events[i].events&EPOLLOUT) // If there is data to send

        {
            sockfd = events[i].data.fd;
            write(sockfd, line, n);
            //Setting file descriptors for read operations

            ev.data.fd=sockfd;
            //Set Read Action Events for Annotation

            ev.events=EPOLLIN|EPOLLET;
            //Modify the event to be processed on sockfd to EPOLIN

            epoll_ctl(epfd,EPOLL_CTL_MOD,sockfd,&ev);
        }
    }
}
return 0;

}

Answer 1

So how does events[i].data.fd contain the socket file descriptor?

它是由 epoll_wait() 放在那里的。它用有关发生的所有事件的信息填充 events 数组。

Why do we set ev.data.fd=listenfd; if we have an array of epoll_event, which has a file descriptor data member?

ev用于注册等待epoll_ctl()的事件，events数组包含发生的事件。

epoll return 如何得到正确的文件描述符

How does epoll return the correct file descriptor

c++

linux

network-programming

epoll