Could you recommend some guides about Epoll on Linux

Question

I need to know about Epoll On linux System.

Could you recommend manual or guides about epoll library?

need more detailed guides. it's better to have some examples.

help me. and Thank you for reading.

Answer 1

Here's an introduction to Epoll, a pretty basic tutorial: http://blog.kovyrin.net/2006/04/13/epoll-asynchronous-network-programming/

A more complete example can be found here: https://banu.com/blog/2/how-to-use-epoll-a-complete-example-in-c/

Also, the man pages

Answer 2

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/epoll.h>

#define PORT 1500 

#define MAX_CON (1200)

static struct epoll_event *events;

int main(int argc, char *argv[])
{
    fd_set master;
    fd_set read_fds;
    struct sockaddr_in serveraddr;
    struct sockaddr_in clientaddr;
    int fdmax;
    int listener;
    int newfd;
    char buf[1024];
    int nbytes;
    int addrlen;
    int yes;
    int epfd = -1;
    int res = -1;
    struct epoll_event ev;
    int i=0;
    int index = 0;
    int client_fd = -1;

    int SnumOfConnection = 0;
    time_t Sstart, Send;

    if((listener = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
            perror("Server-socket() error lol!");
            exit(1);
    }

    if(setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1)
    {
            perror("Server-setsockopt() error lol!");
            exit(1);
    }
    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(listener, (struct sockaddr *)&serveraddr, sizeof(serveraddr)) == -1)
    {
            perror("Server-bind() error lol!");
            exit(1);
    }
    if(listen(listener, 10) == -1)
    {
            perror("Server-listen() error lol!");
            exit(1);
    }
    fdmax = listener; /* so far, it's this one*/

    events = calloc(MAX_CON, sizeof(struct epoll_event));
    if ((epfd = epoll_create(MAX_CON)) == -1) {
            perror("epoll_create");
            exit(1);
    }
    ev.events = EPOLLIN;
    ev.data.fd = fdmax;
    if (epoll_ctl(epfd, EPOLL_CTL_ADD, fdmax, &ev) < 0) {
            perror("epoll_ctl");
            exit(1);
    }
    //time(&start);
    for(;;)
    {
            res = epoll_wait(epfd, events, MAX_CON, -1);
            client_fd = events[index].data.fd;

            for (index = 0; index < MAX_CON; index++) {
                    if(client_fd == listener)
                    {
                            addrlen = sizeof(clientaddr);
                            if((newfd = accept(listener, (struct sockaddr *)&clientaddr, &addrlen)) == -1)
                            {
                                    perror("Server-accept() error lol!");
                            }
                            else
                            {
                            //      printf("Server-accept() is OK...\n");
                                    ev.events = EPOLLIN;
                                    ev.data.fd = newfd;
                                    if (epoll_ctl(epfd, EPOLL_CTL_ADD, newfd, &ev) < 0) {
                                            perror("epoll_ctl");
                                            exit(1);
                                    }
                            }
                            break;
                    }
                    else
                    {
                            if (events[index].events & EPOLLHUP)
                            {
                                    if (epoll_ctl(epfd, EPOLL_CTL_DEL, client_fd, &ev) < 0) {
                                            perror("epoll_ctl");
                                    }
                                    close(client_fd);
                                    break;
                            }
                            if (events[index].events & EPOLLIN)  {
                                    if((nbytes = recv(client_fd, buf, sizeof(buf), 0)) <= 0)
                                    {
                                            if(nbytes == 0) {
                                            //      printf("socket %d hung up\n", client_fd);
                                            }
                                            else {
                                                    printf("recv() error lol! %d", client_fd);
                                                    perror("");
                                            }

                                            if (epoll_ctl(epfd, EPOLL_CTL_DEL, client_fd, &ev) < 0) {
                                                    perror("epoll_ctl");
                                            }
                                            close(client_fd);
                                    }
                                    else
                                    {
                                            if(send(client_fd, buf, nbytes, 0) == -1)
                                                    perror("send() error lol!");
                                    }
                                    break;
                            }
                    }
            }
    }
    return 0;
}

I wrote this program for testing and I was able to connect more than 80k connections and I find average system load only to 0.27%.