accept/epoll problem - linux

Question

I have this code that uses epoll and it has a problem. When I run it, it gives output:
Server-socket() is OK...
Server-bind() is OK...
3
4
accept: Invalid argument
I'm running it on ubuntu linux, system updated, both as limited user and root
what is wrong with the input to accept? What should I change?
struct epoll_event ev, events[MAX_EVENTS];
struct sockaddr_in serveraddr;
int listen_sock, conn_sock, nfds, epollfd;
int yes = 1;
/* Set up listening socket, 'listen_sock' (socket(),
bind(), listen()) */
if((listen_sock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
perror("Server-socket() error lol!");
//just exit lol!
exit(1);
}
printf("Server-socket() is OK...\n");
//"address already in use" error message
/*if(setsockopt(listen_sock, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1)
{
perror("Server-setsockopt() error lol!");
exit(1);
}
printf("Server-setsockopt() is OK...\n");*/
// bind
serveraddr.sin_family = AF_INET;
serveraddr.sin_addr.s_addr = INADDR_ANY;
serveraddr.sin_port = htons(PORT);
memset(&(serveraddr.sin_zero), '\0', 8);
if(bind(listen_sock, (struct sockaddr *)&serveraddr, sizeof(serveraddr)) == -1)
{
perror("Server-bind() error lol!");
exit(1);
}
printf("Server-bind() is OK...\n");
epollfd = epoll_create(MAX_EVENTS);
if (epollfd == -1) {
perror("epoll_create");
exit(EXIT_FAILURE);
}
ev.events = EPOLLIN;
ev.data.fd = listen_sock;
if (epoll_ctl(epollfd, EPOLL_CTL_ADD, listen_sock, &ev) == -1) {
perror("epoll_ctl: listen_sock");
exit(EXIT_FAILURE);
}
for (;;) {
nfds = epoll_wait(epollfd, events, MAX_EVENTS, -1);
if (nfds == -1) {
perror("epoll_pwait");
exit(EXIT_FAILURE);
}
for (int n = 0; n < nfds; ++n) {
if (events[n].data.fd == listen_sock) {
struct sockaddr_in clientaddr;
socklen_t addrlen = sizeof(clientaddr);
cout <<listen_sock <<'\n' <<epollfd <<'\n';
conn_sock = accept(listen_sock, (struct sockaddr *) &clientaddr, &addrlen);
if (conn_sock == -1) {
perror("accept");
exit(EXIT_FAILURE);
}
fcntl(conn_sock, F_SETFL, fcntl(conn_sock, F_GETFD, 0)|O_NONBLOCK);
ev.events = EPOLLIN | EPOLLET;
ev.data.fd = conn_sock;
if (epoll_ctl(epollfd, EPOLL_CTL_ADD, conn_sock,
&ev) == -1) {
perror("epoll_ctl: conn_sock");
exit(EXIT_FAILURE);
}
} else {
printf("%d\n", events[n].data.fd);
}
}
}

Answer 1

You forgot to call listen() after bind():
listen(listen_sock, 5);

Answer 2

I built your source and had the same results. The epoll_wait returns immediately even though there is nothing to accept.
It appears to be the case that using epoll_wait instead of listen is not supported behavior.