epoll经典代码示例

1. epoll原理

原理性的知识不再另做说明，我在这里附上收藏整理的两篇经典文章：

select与epoll的本质关系。

select、poll、epoll之间的区别。

2. epoll服务器端经典示例

2.1 逻辑框架

2.2 代码

#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>

#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 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, true);/*对connfd开启ET模式*/
		}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");
			while(1){
				memset(buf, 0, BUFFER_SIZE);
				int ret  = recv(sockfd, buf, BUFFER_SIZE-1, 0);
				if(ret < 0){
					/*对于非阻塞IO，下面的事件成立标识数据已经全部读取完毕。此后，epoll就能再次触发sockfd上的sockfd的EPOLLIN事件，以驱动下一次读操作*/
					if((errno == EAGAIN) || (errno == EWOULDBLOCK)){
						printf("read later\n");
						break;
					}
					close(sockfd);
					break;
				}else if(ret == 0){
					close(sockfd);
				}else{
					printf("get %d bytes of content: %s\n", ret, buf);
				}

			}
		}else{
			printf("something else happen\n");
		}

	}

}

int main(int argc, char *argv[])
{
	if(argc <= 2){
		printf("Usage: %s ip_address port_number\n", argv[0]);
		return 1;
	}
	const char *ip = argv[1];
	int port = atoi(argv[2]);

	int ret = 0;
	struct sockaddr_in address;
	bzero(&address, sizeof(address));

	address.sin_family = AF_INET;
	inet_pton(AF_INET, ip, &address.sin_addr);
	address.sin_port = htons(port);

	int listenfd = socket(AF_INET, SOCK_STREAM, 0);
	assert(listenfd >= 0);

	ret = bind(listenfd, (struct sockaddr *)&address, sizeof(address));
	assert(ret != -1);

	int opt = 1;
	setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));

	ret = listen(listenfd, 5);
	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;
}