Could you recommend some guides about Epoll on Linux [closed]

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.

Dirtcheap

I have used epoll() extensively, and it's great. I have tested it with 128K active sockets, and it performs extremely well. If you have any specific questions, please ask. – Avina

Thank you. You did great job!! 128k sockets!! awesome! Can you tell me any comment or sample how to accept 128k active sockets? ps : It's too long to answer. I am sorry. – Dirtcheap

@Simon: It is simple to get that many when you accept connections from clients with different IPs. Each IP is limited to 64K ports theoretically and probably 20-30K in practice. You probably want multiple test systems. – Citron

I think this question shall not be closed, it asking for the knowledge about how to use epoll. – Stabilizer

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

Junkie

Second and third link are broken. – Foskett

Third link leads to a phising page – Osteoma

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%.

Makebelieve

you cant use calloc in cpp like that. You should cast it with (epoll_event*) like this : events =(epoll_event*) calloc(MAX_CON, sizeof(struct epoll_event)); – Briony

Ughh.. the code needs cleanup with lots of unused variables only needed when using select – Norty