[系统运维]linux下多路复用实现之Epoll

Epoll相关的API：

int epoll_create(int size);

epoll在内核中维护一个事件表，将用户关心的文件描述符都放进去，因此无需像select和poll那样每次调用都要重复传入文件描述符或事件集，但epoll需要一个额外的文件描述符来唯一标识内核中的这个事件表。

int epoll_ctl(int epfd, int op, int fd, struct epoll_event* event);

op:
   EPOLL_CTL_ADD：往事件表中注册fd上的事件
   EPOLL_CTL_MOD：修改fd上注册的事件
   EPOLL_CTL_DEL：删除fd上注册的事件

event:该参数指定要传入的文件描述符上关注的事件，它是epoll_event结构体指针类型，epoll_event定义如下

struct epoll_event{
    __uint32_t events;   //epoll事件
    epoll_data_t data;  //用户数据
};
其中data用于存储用户数据，它是一个共用体，如下是data定义:
typedef union epoll_data
{
    void *ptr;
    int fd;
    uint32_t u32;
    uint64_t u64;
}epoll_data_t;

int epoll_wait(int epfd, struct_event* events, int maxevents, int timeout);

 - epfd：内核事件表
 - events：用户指定的写入就绪事件的结构体数组，由内核来修改
 - maxevents：最大监听事件个数
 - timeout：阻塞时间，含义与poll中相同
 - 返回值：就绪文件描述符个数

如下是用epoll实现的服务端代码：

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

/* 出错处理 */
void err_exit(char *msg)
{
    perror(msg);
    exit(1);
}

/* 创建socket */
int create_socket(const char *ip, int port)
{
    struct sockaddr_in server_addr;
    int sockfd, reuse = 1;

    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(port);

    if (inet_pton(PF_INET, ip, &server_addr.sin_addr) == -1)
        err_exit("inet_pton() error");

    if ((sockfd = socket(PF_INET, SOCK_STREAM, 0)) == -1)
        err_exit("socket() error");

    /* 设置复用socket地址 */
    if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse)) == -1)
        err_exit("setsockopt() error");

    if (bind(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1)
        err_exit("bind() error");

    if (listen(sockfd, 5) == -1)
        err_exit("listen() error");

    return sockfd;
}

int main()
{
    int listenFd = create_socket("127.0.0.1", 9977);
    printf("create listen fd:%d\n", listenFd);

    int epfd = epoll_create(10);
    printf("create epoll fd:%d\n", epfd);

    struct epoll_event event;
    event.events = EPOLLIN;
    event.data.fd = listenFd;
    epoll_ctl(epfd, EPOLL_CTL_ADD, listenFd, &event);

    while(1)
    {
        struct epoll_event events[100];
        int num = epoll_wait(epfd, events, 100, -1);
        printf("epoll wait fd num:%d\n", num);
        int i = 0;
        for(i = 0; i < num; i++)
        {
        	if(events[i].events & EPOLLRDHUP)
			{
			    int fd = events[i].data.fd;
				printf("%d closed\n", fd);
				epoll_ctl(epfd, EPOLL_CTL_DEL, fd, NULL);
			}
			else if(events[i].events & EPOLLIN)
            {
                int fd = events[i].data.fd;
                if(listenFd == events[i].data.fd)
                {
                    struct sockaddr_in cli;
                    socklen_t len = sizeof(cli);
                    int clientFd = accept(listenFd, (struct sockaddr*)&cli, &len);
                    char ip[16];
                    memset(ip,0,sizeof(ip));
                    inet_ntop(AF_INET,&cli.sin_addr.s_addr,ip,sizeof(ip));
                    printf("client[%s:%d] has connected to server!\n", ip, ntohs(cli.sin_port));

                    struct epoll_event event;
                    event.events = EPOLLIN|EPOLLRDHUP;
                    event.data.fd = clientFd;
                    epoll_ctl(epfd, EPOLL_CTL_ADD, clientFd, &event);
                }else
                {
                    char buff[128] = {0};
                    int ret = recv(fd, buff, 127, 0);

                    printf("%d: %s\n", fd, buff);
                    send(fd, "OK", 2, 0);
                }

            }
        }
    }
    return 0;
}

tcp实现的客户端:

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

int main()
{
    int sockfd = socket(PF_INET, SOCK_STREAM, 0);
    if(sockfd < 0)
    {
        perror("create socket failed\n");
        exit(-1);
    }
    printf("tcp client fd:%d\n", sockfd);
    struct sockaddr_in ser;
    ser.sin_family = AF_INET;
    ser.sin_port = htons(9977);
    ser.sin_addr.s_addr = inet_addr("127.0.0.1");


    if(connect(sockfd, (struct sockaddr*)&ser, sizeof(ser)) < 0)
    {
        perror("connect error");
        exit(-1);
    }
    while(1)
    {
        char buf[128] = {0x00};
        int i = 0;
        sprintf(buf, "tcp client send msg count:%d", ++i);
        if(send(sockfd, buf, strlen(buf), 0) < 0)
            printf("tcp client send failed.\n");

        memset(buf, 0, sizeof(buf));
        ssize_t recvLen = recv(sockfd, buf, sizeof(buf)-1, 0);
        if(recvLen < 0)
            printf("tcp client recv failed, ret value:%d\n",recvLen);
        printf("tcp client recv data:[%s]\n", buf);
        sleep(5);
    }
    return 0;
}