Unix系统编程(8) - I/O多路复用之epoll（Linux）

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1. epoll的由来

epoll是在Linux 2.6.28内核提出的，是select和poll的强化升级版本。相比select和poll，epoll更灵活，没有描述符限制。epoll在Unix中是没有的。
epoll使用一个文件描述符管理多个描述符，将用户关系的文件描述符的事件存放到内核的一个事件表中，这样在用户空间和内核空间的copy只需一次。

2. epoll的使用

Linux 2.6.28之后的系统提供了如下的一组API，这不同于之前的select和poll，他们都只是一个单个的函数。

#include <sys/epoll.h>int epoll_create(int size);int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);int epoll_wait(int epfd, struct epoll_event * events, int maxevents, int timeout);

#include <stdio.h>#include <stdlib.h>#include <sys/types.h>#include <unistd.h>#include <sys/socket.h>#include <netinet/in.h>#include <string.h>#include <arpa/inet.h>#include <pthread.h>#include <sys/time.h>#include <sys/epoll.h>#define SERV_PORT 8000#define MAXLINE 1024#define OPEN_MAX 1024int main(){    int listenfd, connfd, client[OPEN_MAX], efd;    struct sockaddr_in server_addr, client_addr;    struct epoll_event tep, ep[OPEN_MAX];    int i = 0, maxi, nready, clientlen, sockfd, n, j=0, res;    char buf[MAXLINE];    listenfd = socket(AF_INET, SOCK_STREAM, 0);    bzero(&server_addr, sizeof(server_addr));        server_addr.sin_port = htons(SERV_PORT);    server_addr.sin_family = AF_INET;    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);    bind(listenfd, (struct sockaddr *)&server_addr, sizeof(server_addr));    listen(listenfd, 20);    maxi = -1;    for(i=1; i<OPEN_MAX; ++i)        client[i] = -1;    efd = epoll_create(OPEN_MAX);    if(efd == -1)    {        printf("epoll_create error!\n");        exit(-1);    }    tep.events = EPOLLIN;    tep.data.fd = listenfd;    res = epoll_ctl(efd, EPOLL_CTL_ADD, listenfd, &tep);    if(res == -1)    {        printf("epoll_ccl error!\n");        exit(-1);    }    while(1)    {        nready = epoll_wait(efd, ep, OPEN_MAX, -1);        if(nready == -1)        {            printf("epoll_wait error!\n");            exit(-1);        }        for(i=0; i<nready; ++i)        {            if(!(ep[i].events & EPOLLIN))                continue;            if(ep[i].data.fd == listenfd)            {                clientlen = sizeof(client_addr);                connfd = accept(listenfd, (struct sockaddr*)&client_addr, &clientlen);                for(j=0;j<OPEN_MAX;++j)                {                    if(client[j] < 0)                    {                        client[j] = connfd;                        break;                    }                    if(j == OPEN_MAX)                        printf("too many clients\n");                    if(j > maxi)                        maxi = j;                    tep.events = EPOLLIN;                    tep.data.fd = connfd;                    res = epoll_ctl(efd, EPOLL_CTL_ADD, connfd, &tep);                    if(res == -1)                    {                        printf("epoll_ctl error!\n");                        exit(-1);                    }                }            }            else            {                sockfd = ep[i].data.fd;                n = read(sockfd, buf, MAXLINE);                if(0 == n)                {                    for(j=0; j <= maxi; ++j)                    {                        if(client[j] == sockfd)                        {                            client[i] = -1;                            break;                        }                    }                    res = epoll_ctl(efd, EPOLL_CTL_DEL, sockfd, NULL);                    if(res == -1)                    {                        printf("epoll_ctl error\n");                        exit(-1);                    }                    close(sockfd);                }                else                    write(sockfd, buf, n);            }        }    }    close(listenfd);    close(efd);    return 0;}

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