UDP epoll 只檢測單端口的數據

Question

我試圖實現一個程序來了解 UDP epoll 的實際工作。 我已經完成了如下代碼。 這適用於單個套接字。 但是當我嘗試使用多個套接字時（比如 4 sockets 代表 10000、10001、10002、10003），它只檢測到最后一個套接字上的數據（這里是第 4 個，即 10003）。 有人看我的代碼，讓我知道這里有什么問題嗎？

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

#define MAX_EVENTS 20
#define MAXLINE    1024

int get_new_socket(int port)
{
    int sockfd;
    struct sockaddr_in servaddr;

    if ((sockfd = socket(PF_INET, SOCK_DGRAM /*|SOCK_NONBLOCK|SOCK_CLOEXEC*/, IPPROTO_UDP)) < 0 ) {
        perror("socket creation failed");
        exit(EXIT_FAILURE);
    }

    memset(&servaddr, 0, sizeof(servaddr));

    servaddr.sin_family    = AF_INET;
    servaddr.sin_addr.s_addr = INADDR_ANY;
    servaddr.sin_port = htons(port);

    if (bind(sockfd, (const struct sockaddr *)&servaddr,
            sizeof(servaddr)) < 0 )
    {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    return sockfd;
}

void recv_send_data(int sockfd)
{
    char buffer[MAXLINE]; 
    char *hello = "Hello from server"; 
    struct sockaddr_in cliaddr; 
    int ret;

    memset(&cliaddr, 0, sizeof(cliaddr)); 

    int len = sizeof(cliaddr), n = 17; 
    n = recvfrom(sockfd, (char *)buffer, MAXLINE, 0, (struct sockaddr *)&cliaddr, &len);
    perror("recvfrom");
    buffer[n] = '\0'; 
    printf("[%d]Client : %s\n", n, buffer);
    ret = sendto(sockfd, (const char *)hello, 17, 0, (const struct sockaddr *)&cliaddr, len); 

    printf("sent back to client.[%d]\n", ret);
}

int main(int argc, char *argv[]) {
    struct epoll_event ev, events[MAX_EVENTS];
    int listen_sock, nfds, epollfd, n;
    int start_port = 10000;

    for(n = start_port; n < start_port + 4; n++) {
        listen_sock = get_new_socket(n);
        printf("Created socket[%d] for port %d\n", listen_sock, n);
        epollfd = epoll_create1(0);
        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 (;;) {
        printf("Waiting on epoll\n");
        nfds = epoll_wait(epollfd, events, MAX_EVENTS, -1);
        if (nfds == -1) {
            perror("epoll_pwait");
            exit(EXIT_FAILURE);
        }

        printf("EPOLL wait over; processing...\n");
        for (n = 0; n < nfds; ++n) {
            if (events[n].data.fd == listen_sock) {
                printf("Data received on: %d, listen_sock: %d\n", events[n].data.fd, listen_sock);
                recv_send_data(listen_sock);
            }
        }
        sleep(1);
    }
}

Answer 1

為什么要為每個 FD 創建 epoll。 您只需要使用 epoll_create 創建一個 epoll 並用於所有 fd。

epollfd = epoll_create1(0);