epoll()

Posted 2021-12-19 countryboy666

epoll通过在Linux内核中申请一个简易的文件系统(文件系统一般用什么数据结构实现？B+树)。

1）调用epoll_create()建立一个epoll对象(在epoll文件系统中为这个句柄对象分配资源)

2）调用epoll_ctl向epoll对象中添加这100万个连接的套接字

3）调用epoll_wait收集发生的事件的连接

进程启动时建立一个epoll对象，然后在需要的时候向这个epoll对象中添加或者删除连接。同时，epoll_wait的效率也非常高，因为调用epoll_wait时，并没有一股脑的向操作系统复制这100万个连接的句柄数据，内核也不需要去遍历全部的连接。

*/

#include <sys/socket.h>

#include <sys/epoll.h>

#include <netinet/in.h>

#include <arpa/inet.h>

#include <fcntl.h>

#include <unistd.h>

#include <stdio.h>

#include <errno.h>

#include <iostream>

using namespace std;

#define MAX_EVENTS 500

struct myevent_s

    int fd;

    void (*call_back)(int fd, int events, void *arg);

    int events;

    void *arg;

    int status; // 1: in epoll wait list, 0 not in

    char buff[128]; // recv data buffer

    int len, s_offset;

    long last_active; // last active time

;

// set event

void EventSet(myevent_s *ev, int fd, void (*call_back)(int, int, void*), void *arg)

    ev->fd = fd;

    ev->call_back = call_back;

    ev->events = 0;

    ev->arg = arg;

    ev->status = 0;

    bzero(ev->buff, sizeof(ev->buff));

    ev->s_offset = 0;

    ev->len = 0;

    ev->last_active = time(NULL);

// add/mod an event to epoll

void EventAdd(int epollFd, int events, myevent_s *ev)

    struct epoll_event epv = 0, 0;

    int op;

    epv.data.ptr = ev;

    epv.events = ev->events = events;

    if(ev->status == 1)

        op = EPOLL_CTL_MOD;

    else

        op = EPOLL_CTL_ADD;

        ev->status = 1;

    if(epoll_ctl(epollFd, op, ev->fd, &epv) < 0)

        printf("Event Add failed[fd=%d], evnets[%d]\n", ev->fd, events);

    else

        printf("Event Add OK[fd=%d], op=%d, evnets[%0X]\n", ev->fd, op, events);

// delete an event from epoll

void EventDel(int epollFd, myevent_s *ev)

    struct epoll_event epv = 0, 0;

    if(ev->status != 1) return;

    epv.data.ptr = ev;

    ev->status = 0;

    epoll_ctl(epollFd, EPOLL_CTL_DEL, ev->fd, &epv);

int g_epollFd; //global

myevent_s g_Events[MAX_EVENTS+1]; // g_Events[MAX_EVENTS] is used by listen fd  global array

void RecvData(int fd, int events, void *arg);

void SendData(int fd, int events, void *arg);

// accept new connections from clients

void AcceptConn(int fd, int events, void *arg)

    struct sockaddr_in sin;

    socklen_t len = sizeof(struct sockaddr_in);

    int nfd, i;

    // accept

    if((nfd = accept(fd, (struct sockaddr*)&sin, &len)) == -1)

        if(errno != EAGAIN && errno != EINTR)

        printf("%s: accept, %d", __func__, errno);

        return;

    do

        for(i = 0; i < MAX_EVENTS; i++)

            if(g_Events[i].status == 0)

                break;

        if(i == MAX_EVENTS)

            printf("%s:max connection limit[%d].", __func__, MAX_EVENTS);

            break;

        // set nonblocking

        int iret = 0;

        if((iret = fcntl(nfd, F_SETFL, O_NONBLOCK)) < 0)

            printf("%s: fcntl nonblocking failed:%d", __func__, iret);

            break;

        // add a read event for receive data

        EventSet(&g_Events[i], nfd, RecvData, &g_Events[i]);

        EventAdd(g_epollFd, EPOLLIN, &g_Events[i]);

    while(0);

    printf("new conn[%s:%d][time:%d], pos[%d]\n", inet_ntoa(sin.sin_addr),

            ntohs(sin.sin_port), g_Events[i].last_active, i);

// receive data

void RecvData(int fd, int events, void *arg)

    struct myevent_s *ev = (struct myevent_s*)arg;

    int len;

    // receive data

    len = recv(fd, ev->buff+ev->len, sizeof(ev->buff)-1-ev->len, 0);

    EventDel(g_epollFd, ev);

    if(len > 0)

        ev->len += len;

        ev->buff[len] = ‘\0‘;

        printf("C[%d]:%s\n", fd, ev->buff);

        // change to send event

        EventSet(ev, fd, SendData, ev);

        EventAdd(g_epollFd, EPOLLOUT, ev);

    else if(len == 0)

        close(ev->fd);

        printf("[fd=%d] pos[%d], closed gracefully.\n", fd, ev-g_Events);

    else

        close(ev->fd);

        printf("recv[fd=%d] error[%d]:%s\n", fd, errno, strerror(errno));

// send data

void SendData(int fd, int events, void *arg)

    struct myevent_s *ev = (struct myevent_s*)arg;

    int len;

    // send data

    len = send(fd, ev->buff + ev->s_offset, ev->len - ev->s_offset, 0);

    if(len > 0)

        printf("send[fd=%d], [%d<->%d]%s\n", fd, len, ev->len, ev->buff);

        ev->s_offset += len;

        if(ev->s_offset == ev->len)

            // change to receive event

            EventDel(g_epollFd, ev);

            EventSet(ev, fd, RecvData, ev);

            EventAdd(g_epollFd, EPOLLIN, ev);

    else

        close(ev->fd);

        EventDel(g_epollFd, ev);

        printf("send[fd=%d] error[%d]\n", fd, errno);

void InitListenSocket(int epollFd, short port)

    int listenFd = socket(AF_INET, SOCK_STREAM, 0);

    fcntl(listenFd, F_SETFL, O_NONBLOCK); // set non-blocking

    printf("server listen fd=%d\n", listenFd);

    EventSet(&g_Events[MAX_EVENTS], listenFd, AcceptConn, &g_Events[MAX_EVENTS]);

    // add listen socket

    EventAdd(epollFd, EPOLLIN, &g_Events[MAX_EVENTS]);

    // bind & listen

    sockaddr_in sin;

    bzero(&sin, sizeof(sin));

    sin.sin_family = AF_INET;

    sin.sin_addr.s_addr = INADDR_ANY;

    sin.sin_port = htons(port);

    bind(listenFd, (const sockaddr*)&sin, sizeof(sin));

    listen(listenFd, 5);

int main(int argc, char **argv)

    unsigned short port = 12345; // default port

    if(argc == 2)

        port = atoi(argv[1]);

    // create epoll

    g_epollFd = epoll_create(MAX_EVENTS);  //create a epoll obj

    if(g_epollFd <= 0) printf("create epoll failed.%d\n", g_epollFd);

    // create & bind listen socket, and add to epoll, set non-blocking

    InitListenSocket(g_epollFd, port);  //init socket

    // event loop

    struct epoll_event events[MAX_EVENTS];

    printf("server running:port[%d]\n", port);

    int checkPos = 0;

    while(1)

        // a simple timeout check here, every time 100, better to use a mini-heap, and add timer event

        long now = time(NULL);

        for(int i = 0; i < 100; i++, checkPos++) // doesn‘t check listen fd

            if(checkPos == MAX_EVENTS) checkPos = 0; // recycle

            if(g_Events[checkPos].status != 1) continue;

            long duration = now - g_Events[checkPos].last_active;

            if(duration >= 60) // 60s timeout

                close(g_Events[checkPos].fd);

                printf("[fd=%d] timeout[%d--%d].\n", g_Events[checkPos].fd, g_Events[checkPos].last_active, now);

                EventDel(g_epollFd, &g_Events[checkPos]);

        // wait for events to happen

        int fds = epoll_wait(g_epollFd, events, MAX_EVENTS, 1000);

        if(fds < 0)

            printf("epoll_wait error, exit\n");

            break;

        for(int i = 0; i < fds; i++)

            myevent_s *ev = (struct myevent_s*)events[i].data.ptr;

            if((events[i].events&EPOLLIN)&&(ev->events&EPOLLIN)) // read event

                ev->call_back(ev->fd, events[i].events, ev->arg);

            if((events[i].events&EPOLLOUT)&&(ev->events&EPOLLOUT)) // write event

                ev->call_back(ev->fd, events[i].events, ev->arg);

    // free resource

    return 0;