epoll学习

学习参考书：https://book.douban.com/subject/24722611/
epoll是什么？
一个提供多路复用的系统调用

学习要点
参考：http://blog.youkuaiyun.com/yz764127031/article/details/72459158
（1）理解关键字：同步异步，非阻塞阻塞

（2）设置socket为非阻塞，然后利用多路复用检测socket是否可读事件，可读epoll_waiter获取，则通过遍历对相应文件描述符执行相应函数

（3）学习reactor范式，异步事件驱动框架，通过事件触发回调函数

epoll的使用
（1）创建句柄
（2）注册事件
（3）等待事件触发

epoll实例
C语言编写的聊天室实例

用到的知识点有：
epoll
管道
fork
socket基本API

（1）抽象出一个简单的库
提供三个操作：
设置socket为非阻塞
在句柄中添加事件处理函数和socket描述符
向客户端广播聊天信息

#ifndef UTILITY_H_INCLUDED
#define UTILITY_H_INCLUDED

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

using namespace std;

// clients_list save all the clients's socket
list<int> clients_list;

/**********************   macro defintion **************************/
// server ip
#define SERVER_IP "127.0.0.1"

// server port
#define SERVER_PORT 8888

//epoll size
#define EPOLL_SIZE 5000

//message buffer size
#define BUF_SIZE 0xFFFF

#define SERVER_WELCOME "Welcome you join  to the chat room! Your chat ID is: Client #%d"

#define SERVER_MESSAGE "ClientID %d say >> %s"

// exit
#define EXIT "EXIT"

#define CAUTION "There is only one int the char room!"

/**********************   some function **************************/
/**
  * @param sockfd: socket descriptor
  * @return 0
**/
int setnonblocking(int sockfd)
{
    fcntl(sockfd, F_SETFL, fcntl(sockfd, F_GETFD, 0)| O_NONBLOCK);
    return 0;
}

/**
  * @param epollfd: epoll handle
  * @param fd: socket descriptor
  * @param enable_et : enable_et = true, epoll use ET; otherwise LT
**/
void addfd( int epollfd, int fd, bool enable_et )
{
    struct epoll_event ev;
    ev.data.fd = fd;
    ev.events = EPOLLIN;
    if( enable_et )
        ev.events = EPOLLIN | EPOLLET;
    epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &ev);
    setnonblocking(fd);
    printf("fd added to epoll!\n\n");
}

/**
  * @param clientfd: socket descriptor
  * @return : len
**/
int sendBroadcastmessage(int clientfd)
{
    // buf[BUF_SIZE] receive new chat message
    // message[BUF_SIZE] save format message
    char buf[BUF_SIZE], message[BUF_SIZE];
    bzero(buf, BUF_SIZE);
    bzero(message, BUF_SIZE);

    // receive message
    printf("read from client(clientID = %d)\n", clientfd);
    int len = recv(clientfd, buf, BUF_SIZE, 0);

    if(len == 0)  // len = 0 means the client closed connection
    {
        close(clientfd);
        clients_list.remove(clientfd); //server remove the client
        printf("ClientID = %d closed.\n now there are %d client in the char room\n", clientfd, (int)clients_list.size());

    }
    else  //broadcast message 
    {
        if(clients_list.size() == 1) { // this means There is only one int the char room
            send(clientfd, CAUTION, strlen(CAUTION), 0);
            return len;
        }
        // format message to broadcast
        sprintf(message, SERVER_MESSAGE, clientfd, buf);

        list<int>::iterator it;
        for(it = clients_list.begin(); it != clients_list.end(); ++it) {
           if(*it != clientfd){
                if( send(*it, message, BUF_SIZE, 0) < 0 ) { perror("error"); exit(-1);}
           }
        }
    }
    return len;
}
#endif // UTILITY_H_INCLUDED

（2）服务器端编写

#include "utility.h"

int main(int argc, char *argv[])
{
    //服务器IP + port
    struct sockaddr_in serverAddr;
    serverAddr.sin_family = PF_INET;
    serverAddr.sin_port = htons(SERVER_PORT);
    serverAddr.sin_addr.s_addr = inet_addr(SERVER_IP);
    //创建监听socket
    int listener = socket(PF_INET, SOCK_STREAM, 0);
    if(listener < 0) { perror("listener"); exit(-1);}
    printf("listen socket created \n");
    //绑定地址
    if( bind(listener, (struct sockaddr *)&serverAddr, sizeof(serverAddr)) < 0) {
        perror("bind error");
        exit(-1);
    }
    //监听
    int ret = listen(listener, 5);
    if(ret < 0) { perror("listen error"); exit(-1);}
    printf("Start to listen: %s\n", SERVER_IP);
    //在内核中创建事件表
    int epfd = epoll_create(EPOLL_SIZE);
    if(epfd < 0) { perror("epfd error"); exit(-1);}
    printf("epoll created, epollfd = %d\n", epfd);
    static struct epoll_event events[EPOLL_SIZE];
    //往内核事件表里添加事件
    addfd(epfd, listener, true);
    //主循环
    while(1)
    {
        //epoll_events_count表示就绪事件的数目
        int epoll_events_count = epoll_wait(epfd, events, EPOLL_SIZE, -1);
        if(epoll_events_count < 0) {
            perror("epoll failure");
            break;
        }

        printf("epoll_events_count = %d\n", epoll_events_count);
        //处理这epoll_events_count个就绪事件
        for(int i = 0; i < epoll_events_count; ++i)
        {
            int sockfd = events[i].data.fd;
            //新用户连接
            if(sockfd == listener)
            {
                struct sockaddr_in client_address;
                socklen_t client_addrLength = sizeof(struct sockaddr_in);
                int clientfd = accept( listener, ( struct sockaddr* )&client_address, &client_addrLength );

                printf("client connection from: %s : % d(IP : port), clientfd = %d \n",
                inet_ntoa(client_address.sin_addr),
                ntohs(client_address.sin_port),
                clientfd);

                addfd(epfd, clientfd, true);

                // 服务端用list保存用户连接
                clients_list.push_back(clientfd);
                printf("Add new clientfd = %d to epoll\n", clientfd);
                printf("Now there are %d clients int the chat room\n", (int)clients_list.size());

                // 服务端发送欢迎信息  
                printf("welcome message\n");                
                char message[BUF_SIZE];
                bzero(message, BUF_SIZE);
                sprintf(message, SERVER_WELCOME, clientfd);
                int ret = send(clientfd, message, BUF_SIZE, 0);
                if(ret < 0) { perror("send error"); exit(-1); }
            }
            //处理用户发来的消息，并广播，使其他用户收到信息
            else 
            {   
                int ret = sendBroadcastmessage(sockfd);
                if(ret < 0) { perror("error");exit(-1); }
            }
        }
    }
    close(listener); //关闭socket
    close(epfd);    //关闭内核
    return 0;
}

（3）客户端编写

#include "utility.h"

int main(int argc, char *argv[])
{
    //用户连接的服务器 IP + port
    struct sockaddr_in serverAddr;
    serverAddr.sin_family = PF_INET;
    serverAddr.sin_port = htons(SERVER_PORT);
    serverAddr.sin_addr.s_addr = inet_addr(SERVER_IP);

    // 创建socket
    int sock = socket(PF_INET, SOCK_STREAM, 0);
    if(sock < 0) { perror("sock error"); exit(-1); }
    // 连接服务端
    if(connect(sock, (struct sockaddr *)&serverAddr, sizeof(serverAddr)) < 0) {
        perror("connect error");
        exit(-1);
    }

    // 创建管道，其中fd[0]用于父进程读，fd[1]用于子进程写
    int pipe_fd[2];
    if(pipe(pipe_fd) < 0) { perror("pipe error"); exit(-1); }

    // 创建epoll
    int epfd = epoll_create(EPOLL_SIZE);
    if(epfd < 0) { perror("epfd error"); exit(-1); }
    static struct epoll_event events[2]; 
    //将sock和管道读端描述符都添加到内核事件表中
    addfd(epfd, sock, true);
    addfd(epfd, pipe_fd[0], true);
    // 表示客户端是否正常工作
    bool isClientwork = true;

    // 聊天信息缓冲区
    char message[BUF_SIZE];

    // Fork
    int pid = fork();
    if(pid < 0) { perror("fork error"); exit(-1); }
    else if(pid == 0)      // 子进程
    {
        //子进程负责写入管道，因此先关闭读端
        close(pipe_fd[0]); 
        printf("Please input 'exit' to exit the chat room\n");

        while(isClientwork){
            bzero(&message, BUF_SIZE);
            fgets(message, BUF_SIZE, stdin);

            // 客户输出exit,退出
            if(strncasecmp(message, EXIT, strlen(EXIT)) == 0){
                isClientwork = 0;
            }
            // 子进程将信息写入管道
            else {
                if( write(pipe_fd[1], message, strlen(message) - 1 ) < 0 )
                 { perror("fork error"); exit(-1); }
            }
        }
    }
    else  //pid > 0 父进程
    {
        //父进程负责读管道数据，因此先关闭写端
        close(pipe_fd[1]); 

        // 主循环(epoll_wait)
        while(isClientwork) {
            int epoll_events_count = epoll_wait( epfd, events, 2, -1 );
            //处理就绪事件
            for(int i = 0; i < epoll_events_count ; ++i)
            {
                bzero(&message, BUF_SIZE);

                //服务端发来消息
                if(events[i].data.fd == sock)
                {
                    //接受服务端消息
                    int ret = recv(sock, message, BUF_SIZE, 0);

                    // ret= 0 服务端关闭
                    if(ret == 0) {
                        printf("Server closed connection: %d\n", sock);
                        close(sock);
                        isClientwork = 0;
                    }
                    else printf("%s\n", message);

                }
                //子进程写入事件发生，父进程处理并发送服务端
                else { 
                    //父进程从管道中读取数据
                    int ret = read(events[i].data.fd, message, BUF_SIZE);

                    // ret = 0
                    if(ret == 0) isClientwork = 0;
                    else{   // 将信息发送给服务端
                      send(sock, message, BUF_SIZE, 0);
                    }
                }
            }//for
        }//while
    }

    if(pid){
       //关闭父进程和sock
        close(pipe_fd[0]);
        close(sock);
    }else{
        //关闭子进程
        close(pipe_fd[1]);
    }
    return 0;
}