linux socket多连接

# 查看当前文件描述符限制
ulimit -n

# 临时修改限制
ulimit -n 10000

# 永久修改限制（需要编辑/etc/security/limits.conf）
* soft nofile 10000
* hard nofile 10000

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/epoll.h>

#define MAX_EVENTS 10
#define BUFFER_SIZE 1024

void setnonblocking(int sockfd) {
    int opts;
    opts = fcntl(sockfd, F_GETFL);
    if (opts < 0) {
        perror("fcntl(F_GETFL)");
        exit(EXIT_FAILURE);
    }
    opts = (opts | O_NONBLOCK);
    if (fcntl(sockfd, F_SETFL, opts) < 0) {
        perror("fcntl(F_SETFL)");
        exit(EXIT_FAILURE);
    }
}

int main() {
    int listen_fd, conn_fd, epoll_fd, nfds, n;
    struct epoll_event ev, events[MAX_EVENTS];
    char buffer[BUFFER_SIZE];

    listen_fd = socket(AF_INET, SOCK_STREAM, 0);
    if (listen_fd < 0) {
        perror("socket");
        exit(EXIT_FAILURE);
    }

    struct sockaddr_in server_addr;
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(8080);
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);

    if (bind(listen_fd, (struct sockaddr*)&server_addr, sizeof(server_addr)) < 0) {
        perror("bind");
        exit(EXIT_FAILURE);
    }

    if (listen(listen_fd, SOMAXCONN) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    epoll_fd = epoll_create1(0);
    if (epoll_fd < 0) {
        perror("epoll_create1");
        exit(EXIT_FAILURE);
    }

    ev.events = EPOLLIN;
    ev.data.fd = listen_fd;
    if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, listen_fd, &ev) < 0) {
        perror("epoll_ctl: listen_fd");
        exit(EXIT_FAILURE);
    }

    while (1) {
        nfds = epoll_wait(epoll_fd, events, MAX_EVENTS, -1);
        if (nfds < 0) {
            perror("epoll_wait");
            exit(EXIT_FAILURE);
        }

        for (n = 0; n < nfds; ++n) {
            if (events[n].data.fd == listen_fd) {
                conn_fd = accept(listen_fd, (struct sockaddr*)NULL, NULL);
                if (conn_fd < 0) {
                    perror("accept");
                    continue;
                }
                setnonblocking(conn_fd);
                ev.events = EPOLLIN | EPOLLET;
                ev.data.fd = conn_fd;
                if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, conn_fd, &ev) < 0) {
                    perror("epoll_ctl: conn_fd");
                    close(conn_fd);
                }
            } else {
                conn_fd = events[n].data.fd;
                int len = read(conn_fd, buffer, BUFFER_SIZE);
                if (len <= 0) {
                    close(conn_fd);
                    epoll_ctl(epoll_fd, EPOLL_CTL_DEL, conn_fd, &ev);
                } else {
                    write(conn_fd, buffer, len); // Echo back
                }
            }
        }
    }

    close(listen_fd);
    return 0;
}