Linux epoll

int edfd = epoll_create(int size);

生成一个Epoll专用的文件描述符，其实是申请一个内核空间，用来存放你想关注的socket fd上是否发生以及发生了什么事件。size就是你在这个Epoll fd上能关注的最大socket fd数，大小自定，只要内存足够。

int epoll_ctl(int epfd, intop, int fd, structepoll_event *event);

控制某个Epoll文件描述符上的事件：注册、修改、删除。其中参数epfd是epoll_create()创建Epoll专用的文件描述符。相对于select模型中的FD_SET和FD_CLR宏。

intepoll_wait(int epfd,structepoll_event * events,int maxevents,int timeout);

等待I/O事件的发生；参数说明：

epfd:由epoll_create() 生成的Epoll专用的文件描述符；

epoll_event:用于回传代处理事件的数组；

maxevents:每次能处理的事件数；

timeout:等待I/O事件发生的超时值；

返回发生事件数。

相对于select模型中的select函数。

    //     
    // a simple echo server using epoll in linux    
    //     
    // 2009-11-05    
    // 2013-03-22:修改了几个问题，1是/n格式问题，2是去掉了原代码不小心加上的ET模式;  
    // 本来只是简单的示意程序，决定还是加上 recv/send时的buffer偏移  
    // by sparkling    
    //     
    #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;    
    myevent_s g_Events[MAX_EVENTS+1]; // g_Events[MAX_EVENTS] is used by listen fd    
    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);    
        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);    
        // 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;    
    }