Linux编程之epoll示例

基础原理理解请参考这篇：

IO - 同步，异步，阻塞，非阻塞（亡羊补牢篇）

select主要解决的问题：（详细请参考：select用法&原理详解（源码剖析））

select/epoll区别：如果这篇文章说不清epoll的本质，那就过来掐死我吧！

逻辑框架

服务端：

//服务端 gcc server_epoll.c -o server_epoll
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/epoll.h>
#include <pthread.h>
#include <sys/ioctl.h> 

#define true 				1
#define false				0
#define MAX_EVENT_NUMBER 	1024
#define BUFFER_SIZE 		10

/*将文件描述符设置为非阻塞*/
int setnonblocking(int fd)
{
	int old_option = fcntl(fd, F_GETFL);
	int new_option = old_option | O_NONBLOCK;
	fcntl(fd, F_SETFL, new_option);
	return old_option;
}

/*将文件描述符fd上的EPOLLIN注册到epollfd指示的epoll内核事件表中。 参数enable_et 指定是否对fd采用ET模式*/
void addfd(int epollfd, int fd, int enable_et)
{
	struct epoll_event event;
	event.data.fd = fd;
	event.events  = EPOLLIN;
	if(enable_et){
		event.events |= EPOLLET;
	}
	epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event );
	setnonblocking(fd);
}
/*LT 模式的工作原理*/
void lt(struct epoll_event *events, int number, int epollfd, int listenfd)
{
	char buf[BUFFER_SIZE];
	int i = 0;
	for(i= 0;i<number;i++){
		int sockfd = events[i].data.fd;
		if(sockfd == listenfd){
			struct sockaddr_in client_address;
			socklen_t client_addrlength = sizeof(client_address);
			int connfd = accept(listenfd, (struct sockaddr *)&client_address, &client_addrlength);
			addfd(epollfd, connfd, false);
		}else if(events[i].events & EPOLLIN){
			/*只要socket读缓存中的还有未读的数据，此代码就能触发*/
			printf("event trigger once\n");
			memset(buf, 0, BUFFER_SIZE);
			int ret = recv(sockfd, buf, BUFFER_SIZE-1, 0);
			if(ret <= 0){
				close(sockfd);
				continue;
			}
			printf("get %d bytes of content: %s\n", ret, buf);
		}else{
			printf("Something else happen !!!\n");
		}
	}
}

/*ET 模式的工作流程*/
void et(struct epoll_event* events, int number, int epollfd, int listenfd)
{
	char ch;
	int i=0;
	int nread = 0;
	for(i =0; i<number; i++){
		int sockfd = events[i].data.fd;
		if(sockfd == listenfd){
			struct sockaddr_in client_address;
			socklen_t client_addrlength = sizeof(client_address);
			int connfd = accept(listenfd, (struct sockaddr* )&client_address, &client_addrlength);
			addfd(epollfd, connfd, true);/*对connfd开启ET模式*/
			printf("server fd %d adding client on fd %d\n", listenfd, connfd); 
		}else if(events[i].events & EPOLLIN){
			/*这段代码不会被重复触发，所以我们循环读取数据，以确保把socket缓冲区的数据全部读取*/
			printf("Event trigger once !!!\n");
			ioctl(sockfd, FIONREAD, &nread);//取得数据量交给nread
            /*客户数据请求完毕，关闭套接字，从集合中清除相应描述符 */
            if(nread == 0) 
            {
                close(sockfd); 
                printf("removing client on fd %d\n", sockfd); 
            }
            /*处理客户数据请求*/
            else 
            { 
                read(sockfd, &ch, 1); 
                sleep(5); 
                printf("serving read client on fd %d, %c\n", sockfd, ch);
                ch++; 
                write(sockfd, &ch, 1);
				printf("serving write client on fd %d, %c\n", sockfd, ch);
            }
		}else{
			printf("something else happen\n");
		}
	}
}


int main()
{
	int ret = 0;
	struct sockaddr_in address;
	bzero(&address, sizeof(address));
	
    address.sin_family = AF_INET; 
    address.sin_addr.s_addr = htonl(INADDR_ANY); 
    address.sin_port = htons(8888);

	
	int listenfd = socket(AF_INET, SOCK_STREAM, 0);
	assert(listenfd >= 0);
	
	ret = bind(listenfd, (struct sockaddr *)&address, sizeof(address));
	assert(ret != -1);
	
	ret = listen(listenfd, 5);//监听队列最多容纳5个
	assert(ret != -1);
	
	
	struct epoll_event events[MAX_EVENT_NUMBER];
	int epollfd = epoll_create(5);
	assert(epollfd != -1);
	
	addfd(epollfd, listenfd, true);
	while(1){
		int ret = epoll_wait(epollfd, events, MAX_EVENT_NUMBER, -1);
		if(ret<0){
			printf("epoll failure\n");
			break;
		}
		lt(events, ret, epollfd, listenfd);
		//et(events, ret, epollfd, listenfd);
	}
	close(listenfd);
	return 0;
}

客户端：

//客户端 gcc client.c -o client
#include <sys/types.h> 
#include <sys/socket.h> 
#include <stdio.h> 
#include <netinet/in.h> 
#include <arpa/inet.h> 
#include <unistd.h> 
#include <stdlib.h>
#include <sys/time.h>

int main() 
{ 
    int client_sockfd; 
    int len; 
    struct sockaddr_in address;//服务器端网络地址结构体 
     int result; 
    char ch = 'A'; 
    client_sockfd = socket(AF_INET, SOCK_STREAM, 0);//建立客户端socket 
    address.sin_family = AF_INET; 
    address.sin_addr.s_addr = inet_addr("127.0.0.1");
    address.sin_port = htons(8888); 
    len = sizeof(address); 
    result = connect(client_sockfd, (struct sockaddr *)&address, len); 
    if(result == -1) 
    {
         perror("oops: client2"); 
         exit(1); 
    }
	printf("client_sockfd = %d\n", client_sockfd); 
    //第一次读写
    write(client_sockfd, &ch, 1);
	printf("first client write over!\n");
    read(client_sockfd, &ch, 1);
	printf("first client read over!\n");
    printf("the first time: char from server = %c sleep 5s\n", ch); 
    sleep(5);
    
    //第二次读写
    write(client_sockfd, &ch, 1);
	printf("second client write over!\n");
    read(client_sockfd, &ch, 1); 
	printf("second client read over!\n");
    printf("the second time: char from server = %c\n", ch);
    
    close(client_sockfd);
   
    return 0; 
}

执行结果：