I/O 多路复用：`select`、`poll`、`epoll` 和 `kqueue` 的区别与示例

#include <stdio.h>
#include <stdlib.h>
#include <sys/select.h>
#include <unistd.h>

int main() {
    fd_set readfds;
    struct timeval timeout;
    int ret;

    // 初始化文件描述符集合
    FD_ZERO(&readfds);
    FD_SET(STDIN_FILENO, &readfds);

    // 设置超时时间
    timeout.tv_sec = 5;
    timeout.tv_usec = 0;

    printf("Waiting for input, timeout in 5 seconds...\n");
    // 调用 select 函数，监控文件描述符
    ret = select(STDIN_FILENO + 1, &readfds, NULL, NULL, &timeout);

    if (ret == -1) {
        perror("select");
        exit(EXIT_FAILURE);
    } else if (ret == 0) {
        printf("Timeout occurred! No data after 5 seconds.\n");
    } else {
        if (FD_ISSET(STDIN_FILENO, &readfds)) {
            char buffer[1024];
            read(STDIN_FILENO, buffer, sizeof(buffer));
            printf("Data read: %s\n", buffer);
        }
    }

    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <poll.h>
#include <unistd.h>

int main() {
    struct pollfd fds[1];
    int ret;

    // 设置文件描述符和事件
    fds[0].fd = STDIN_FILENO;
    fds[0].events = POLLIN;

    printf("Waiting for input, timeout in 5 seconds...\n");
    // 调用 poll 函数，设置 5 秒超时
    ret = poll(fds, 1, 5000);

    if (ret == -1) {
        perror("poll");
        exit(EXIT_FAILURE);
    } else if (ret == 0) {
        printf("Timeout occurred! No data after 5 seconds.\n");
    } else {
        if (fds[0].revents & POLLIN) {
            char buffer[1024];
            read(STDIN_FILENO, buffer, sizeof(buffer));
            printf("Data read: %s\n", buffer);
        }
    }

    return 0;
}

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

int main() {
    int epfd = epoll_create1(0);
    struct epoll_event event, events[1];
    int ret;

    if (epfd == -1) {
        perror("epoll_create1");
        exit(EXIT_FAILURE);
    }

    // 设置事件
    event.events = EPOLLIN;
    event.data.fd = STDIN_FILENO;

    if (epoll_ctl(epfd, EPOLL_CTL_ADD, STDIN_FILENO, &event) == -1) {
        perror("epoll_ctl");
        exit(EXIT_FAILURE);
    }

    printf("Waiting for input, timeout in 5 seconds...\n");
    // 调用 epoll_wait，等待事件
    ret = epoll_wait(epfd, events, 1, 5000);

    if (ret == -1) {
        perror("epoll_wait");
        exit(EXIT_FAILURE);
    } else if (ret == 0) {
        printf("Timeout occurred! No data after 5 seconds.\n");
    } else {
        if (events[0].data.fd == STDIN_FILENO) {
            char buffer[1024];
            read(STDIN_FILENO, buffer, sizeof(buffer));
            printf("Data read: %s\n", buffer);
        }
    }

    close(epfd);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <sys/event.h>
#include <sys/time.h>
#include <unistd.h>

int main() {
    int kq = kqueue();
    struct kevent change, event;
    int ret;

    if (kq == -1) {
        perror("kqueue");
        exit(EXIT_FAILURE);
    }

    // 设置事件
    EV_SET(&change, STDIN_FILENO, EVFILT_READ, EV_ADD, 0, 0, NULL);

    printf("Waiting for input, timeout in 5 seconds...\n");
    // 调用 kevent，设置 5 秒超时
    struct timespec timeout = {5, 0};
    ret = kevent(kq, &change, 1, &event, 1, &timeout);

    if (ret == -1) {
        perror("kevent");
        exit(EXIT_FAILURE);
    } else if (ret == 0) {
        printf("Timeout occurred! No data after 5 seconds.\n");
    } else {
        if (event.ident == STDIN_FILENO) {
            char buffer[1024];
            read(STDIN_FILENO, buffer, sizeof(buffer));
            printf("Data read: %s\n", buffer);
        }
    }

    close(kq);
    return 0;
}