网络编程——Linux高性能服务器编程阅读日记

Linux高性能服务器编程阅读日记——epoll两种触发模式比较

eopll，LT水平触发和ET边缘触发的区别，写了个简单的服务器代码测试了一下

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

#define MAX_EVENT_NUMBER 1024
#define BUFFER_SIZE 10

//将文件描述符设置成非阻塞的
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;
}

void addfd(int epollfd,int fd,bool enable_et)
{
	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);
}

void lt(epoll_event* events,int number,int epollfd,int listenfd)
{
	char buf[BUFFER_SIZE];
	for(int 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);//对connfd禁用ET模式
		}
		else if(events[i].events&EPOLLIN)
		{
			//只要socket读缓存中还有未读出的数据，这段代码就被触发
			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 happened\n");
	}
}

void et(epoll_event* events,int number,int epollfd,int listenfd)
{
        char buf[BUFFER_SIZE];
        for(int 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);//对connfd禁用ET模式
                }
                else if(events[i].events&EPOLLIN)
                {
                        //只要socket读缓存中还有未读出的数据，这段代码就被触发
                        printf("event trigger once\n");
			while(1)
			{
			        memset(buf,'\0',BUFFER_SIZE);
				int ret = recv(sockfd,buf,BUFFER_SIZE-1,0);
				if(ret<0)
			        {
					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 happened\n");
        }
}

int main(int argc,char* argv[])
{
	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(PF_INET,SOCK_STREAM,0);
	assert(listenfd >= 0);

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

	ret = listen(listenfd,5);
	assert(ret!=-1);

	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 fail");
			break;
		}
		et(events,ret,epollfd,listenfd);
	}

}

telnet模拟http请求发送给服务端可以发现，发送超过十个字符的请求的时候两种模式的处理方式不同，LT模式未读取完成则还可以继续触发epoll事件，ET模式必须每次有IO请求就循环读取结束为止，否则下次不会再触发epoll事件。
看起来是LT模式比较智能，但是实际上，ET模式效率比较高，因为读取IO请求只需要触发一次。