The epoll API

Example code

The following code creates an epoll file descriptor:

int epollfd;

epollfd = epoll_create(5);   /* We'll (probably) monitor 5 fds */

We then repeatedly perform the following steps to add each file descriptor to the interest list.

struct epoll_event ev;

ev.data.fd = fd;             /* Returned via later epoll_wait() */
ev.events = EPOLLIN;         /* Monitor for input */
epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, ev);

Now we can wait for file descriptors in the interest list to become ready:

#define MAX_EVENTS 5   /* Max. items to return from ready list
                          in a single epoll_wait() */
struct epoll_event evlist[MAX_EVENTS]

ready = epoll_wait(epollfd, evlist, MAX_EVENTS, -1);

for (j = 0; j < ready; j++) {
    if (evlist[j].events & EPOLLIN) {
        s = read(evlist[j].data.fd, buf, MAX_BUF);
        printf("    read %d bytes: %.*s\n", s, s, buf);
    } 
    if (evlist[j].events & (EPOLLHUP | EPOLLERR)) 
        close(evlist[j].data.fd);    /* End-of-file or error */
}

Notice that the number of the ready file descriptor was obtained via evlist[j].data.fd.