9-4oneshot.cpp

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

#define MAX_EVENT_NUMBER 1024
#define BUFFER_SIZE 1024
struct fds
{
    int epollfd;
    int sockfd;
};

int setnonblocking(int fd)
{
    int old_option = fcntl(fd, F_GETFL);
    int new_option = old_option | O_NONBLOCK;
    fcntl(fd, F_SETFL, new_option);
    return old_option;
}

// 将 fd 上的 EPOLLIN 和 EPOLLET 事件注册到 epollfd 指示的 epoll 内核事件表中
void addfd(int epollfd, int fd, bool oneshot)
{
    epoll_event event;
    event.data.fd = fd;
    event.events = EPOLLIN | EPOLLET;
    if (oneshot) // 指定是否注册 fd 上的 EPOLLONESHOT 事件
    {
        event.events |= EPOLLONESHOT;
    }
    epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event);
    setnonblocking(fd);
}

// 重置 fd 上的事件，这样操作之后，尽管 fd 上的 EPOLLONESHOT 事件被注册
// 但是操作系统仍然会触发 fd 上的 EPOLLIN 事件，且只触发一次
void reset_oneshot(int epollfd, int fd)
{
    epoll_event event;
    event.data.fd = fd;
    event.events = EPOLLIN | EPOLLET | EPOLLONESHOT;
    epoll_ctl(epollfd, EPOLL_CTL_MOD, fd, &event);
}

// 工作线程
void *worker(void *arg)
{
    int sockfd = ((fds *)arg)->sockfd;
    int epollfd = ((fds *)arg)->epollfd;
    printf("start new thread to receive data on fd: %d\n", sockfd);
    char buf[BUFFER_SIZE];
    memset(buf, '\0', BUFFER_SIZE);
    // 循环读取 sockfd 上的数据，直到遇到 EAGAIN 错误
    while (1)
    {
        int ret = recv(sockfd, buf, BUFFER_SIZE - 1, 0);
        if (ret == 0)
        {
            close(sockfd);
            printf("foreigner closed the connection\n");
            break;
        }
        else if (ret < 0)
        {
            // 此时客户端的数据发送完毕，重置 EPOLL 事件，让其他线程有机会为该 socket 服务
            if (errno == EAGAIN)
            {
                reset_oneshot(epollfd, sockfd);
                printf("read later\n");
                break;
            }
        }
        else
        {
            printf("get content: %s\n", buf);
            sleep(5);   // 休眠 5s，模拟数据处理过程
        }
    }
    printf("end thread receiving data on fd: %d\n", sockfd);
}

int main(int argc, char *argv[])
{
    if (argc <= 2)
    {
        printf("usage: %s ip_address port_number\n", basename(argv[0]));
        return 1;
    }
    const char *ip = argv[1];
    int port = atoi(argv[2]);

    int ret = 0;
    struct sockaddr_in address;
    bzero(&address, sizeof(address));
    address.sin_family = AF_INET;
    inet_pton(AF_INET, ip, &address.sin_addr);
    address.sin_port = htons(port);

    int listenfd = socket(PF_INET, SOCK_STREAM, 0);
    assert(listenfd >= 0);

    ret = bind(listenfd, (struct sockaddr *)&address, sizeof(address));
    assert(ret != -1);

    ret = listen(listenfd, 5);
    assert(ret != -1);

    epoll_event events[MAX_EVENT_NUMBER];
    int epollfd = epoll_create(5);
    assert(epollfd != -1);
    // 监听 socket listenfd 上是不能注册 EPOLLONESHOT 事件的，否则应用程序只能处理一个客户连接
    // 因为后续的客户连接将不再触发 listenfd 上的 EPOLLIN 事件
    addfd(epollfd, listenfd, false);

    while (1)
    {
        int ret = epoll_wait(epollfd, events, MAX_EVENT_NUMBER, -1);
        if (ret < 0)
        {
            printf("epoll failure\n");
            break;
        }

        for (int i = 0; i < ret; i++)
        {
            int sockfd = events[i].data.fd;
            if (sockfd == listenfd)
            {
                struct sockaddr_in client_address;
                socklen_t client_addrlength = sizeof(client_address);
                int connfd = accept(listenfd, (struct sockaddr *)&client_address, &client_addrlength);
                // 对每个非监听的 fd 都注册 EPOLLONESHOT 事件
                addfd(epollfd, connfd, true);
            }
            else if (events[i].events & EPOLLIN)
            {
                pthread_t thread;
                fds fds_for_new_worker;
                fds_for_new_worker.epollfd = epollfd;
                fds_for_new_worker.sockfd = sockfd;
                // 启动一个工作线程为 sockfd 服务
                pthread_create(&thread, NULL, worker, (void *)&fds_for_new_worker);
            }
            else
            {
                printf("something else happened \n");
            }
        }
    }

    close(listenfd);
    return 0;
}