curl https://banu.com/blog/2/how-to-use-epoll-a-complete-example-in-c/epoll-example.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/epoll.h>
#include <errno.h>
#define MAXEVENTS 64
static int make_socket_non_blocking(int sfd) {
int flags, s;
flags = fcntl(sfd, F_GETFL, 0);
if (flags == -1) {
perror("fcntl");
return -1;
}
flags |= O_NONBLOCK;
s = fcntl(sfd, F_SETFL, flags);
if (s == -1) {
perror("fcntl");
return -1;
}
return 0;
}
static int create_and_bind(char *port) {
struct addrinfo hints;
struct addrinfo *result, *rp;
int s, sfd;
memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_family = AF_UNSPEC; /* Return IPv4 and IPv6 choices */
hints.ai_socktype = SOCK_STREAM; /* We want a TCP socket */
hints.ai_flags = AI_PASSIVE; /* All interfaces */
s = getaddrinfo(NULL, port, &hints, &result);
if (s != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
return -1;
}
for (rp = result; rp != NULL; rp = rp->ai_next) {
sfd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
if (sfd == -1)
continue;
s = bind(sfd, rp->ai_addr, rp->ai_addrlen);
if (s == 0) {
/* We managed to bind successfully! */
break;
}
close(sfd);
}
if (rp == NULL) {
fprintf(stderr, "Could not bind\n");
return -1;
}
freeaddrinfo(result);
return sfd;
}
int main(int argc, char *argv[]) {
int sfd, s;
int efd;
struct epoll_event event;
struct epoll_event *events;
if (argc != 2) {
fprintf(stderr, "Usage: %s [port]\n", argv[0]);
exit(EXIT_FAILURE);
}
sfd = create_and_bind(argv[1]);
if (sfd == -1)
abort();
s = make_socket_non_blocking(sfd);
if (s == -1)
abort();
s = listen(sfd, SOMAXCONN);
if (s == -1) {
perror("listen");
abort();
}
efd = epoll_create1(0);
if (efd == -1) {
perror("epoll_create");
abort();
}
event.data.fd = sfd;
event.events = EPOLLIN | EPOLLET;
s = epoll_ctl(efd, EPOLL_CTL_ADD, sfd, &event);
if (s == -1) {
perror("epoll_ctl");
abort();
}
/* Buffer where events are returned */
events = calloc(MAXEVENTS, sizeof event);
/* The event loop */
while (1) {
int n, i;
n = epoll_wait(efd, events, MAXEVENTS, -1);
for (i = 0; i < n; i++) {
if ((events[i].events & EPOLLERR) || (events[i].events & EPOLLHUP) || (!(events[i].events & EPOLLIN))) {
/* An error has occured on this fd, or the socket is not
ready for reading (why were we notified then?) */
fprintf(stderr, "epoll error\n");
close(events[i].data.fd);
continue;
}
else if (sfd == events[i].data.fd) {
/* We have a notification on the listening socket, which
means one or more incoming connections. */
while (1) {
struct sockaddr in_addr;
socklen_t in_len;
int infd;
char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
in_len = sizeof in_addr;
infd = accept(sfd, &in_addr, &in_len);
if (infd == -1) {
if ((errno == EAGAIN) || (errno == EWOULDBLOCK)) {
/* We have processed all incoming
connections. */
break;
} else {
perror("accept");
break;
}
}
s = getnameinfo(&in_addr, in_len, hbuf, sizeof hbuf, sbuf, sizeof sbuf, NI_NUMERICHOST | NI_NUMERICSERV);
if (s == 0) {
printf("Accepted connection on descriptor %d "
"(host=%s, port=%s)\n", infd, hbuf, sbuf);
}
/* Make the incoming socket non-blocking and add it to the
list of fds to monitor. */
s = make_socket_non_blocking(infd);
if (s == -1)
abort();
event.data.fd = infd;
event.events = EPOLLIN | EPOLLET;
s = epoll_ctl(efd, EPOLL_CTL_ADD, infd, &event);
if (s == -1) {
perror("epoll_ctl");
abort();
}
}
continue;
} else {
/* We have data on the fd waiting to be read. Read and
display it. We must read whatever data is available
completely, as we are running in edge-triggered mode
and won't get a notification again for the same
data. */
int done = 0;
while (1) {
ssize_t count;
char buf[512];
count = read(events[i].data.fd, buf, sizeof buf);
if (count == -1) {
/* If errno == EAGAIN, that means we have read all
data. So go back to the main loop. */
if (errno != EAGAIN) {
perror("read");
done = 1;
}
break;
} else if (count == 0) {
/* End of file. The remote has closed the
connection. */
done = 1;
break;
}
/* Write the buffer to standard output */
s = write(1, buf, count);
if (s == -1) {
perror("write");
abort();
}
}
if (done) {
printf("Closed connection on descriptor %d\n", events[i].data.fd);
/* Closing the descriptor will make epoll remove it
from the set of descriptors which are monitored. */
close(events[i].data.fd);
}
}
}
}
free(events);
close(sfd);
return EXIT_SUCCESS;
}