1. 程式人生 > >epoll函式——ET模式與LT模式的區別

epoll函式——ET模式與LT模式的區別

LT模式(普通模式):也叫水平觸發。描述符上有資料就緒,如果使用者沒有處理完,可以反覆提醒,當下一輪I/O函式執行時會繼續提醒使用者該描述符上有資料,直到使用者將資料讀完為止。

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <assert.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#define MAXFD 10
 
void epoll_add(int epfd,int fd)//往核心事件表中新增檔案描述符
{
	struct epoll_event ev;
	ev.events = EPOLLIN;//註冊讀事件,設定關注
    ev.data.fd = fd;
    if(epoll_ctl(epfd,EPOLL_CTL_ADD,fd,&ev )== -1)  
    //EPOLL_CTL_ADD為操作方法新增
    {  
        perror("epoll_ctl add error");  
	}
    
}
void epoll_del(int epfd,int fd)//從核心事件表中移除檔案描述符
{
	if(epoll_ctl(epfd,EPOLL_CTL_DEL,fd,NULL) == -1 )
    //EPOLL_CTL_ADD為操作方法移除
	{
		perror("epoll_ctl del error");
	}
}
 
int main()   
{   
	int sockfd = socket(AF_INET,SOCK_STREAM,0);
	assert(sockfd != -1);
 
	struct sockaddr_in saddr,caddr;
	memset(&saddr,0,sizeof(saddr));
	saddr.sin_family = AF_INET;
	saddr.sin_port = htons(6000);
	saddr.sin_addr.s_addr = inet_addr("127.0.0.1");
 
	int res = bind(sockfd,(struct sockaddr *)&saddr,sizeof(saddr));
	assert(res != -1);
 
	listen(sockfd,5);
	assert(sockfd != -1);
 
    int epfd = epoll_create(MAXFD);  
    //系統呼叫,在核心空間中建立核心事件表,實際為一種紅黑樹的資料結構
    if(epfd == -1)  
    {  
        perror("epoll_create failed");  
   
    }  
     
	epoll_add(epfd,sockfd);//把事件和檔案描述符新增到紅黑樹中的結點中去
    struct epoll_event events[MAXFD]; 
    //因為epoll_wait()會把就緒的檔案描述符存在一個數組中,所以定義這個陣列
 
    while(1)  
    {  
        printf("epoll wait\n");
        int n = epoll_wait(epfd,events,MAXFD,5000);  
        //檢查就緒並且將其新增到events這個陣列中
        if(n == -1)  //失敗
        {  
            perror("epoll_wait error");  
            continue;
        }  
		else  if(n == 0)//超時
		{
			printf("time out\n");
			continue;
		}
        //有n個數據元素就緒
		else
		{
			int i = 0;  
			for(;i < n;i++)  
			{  
				int fd = events[i].data.fd;
			    if(events[i].events & POLLIN)
                //因為有多種事件,因此要檢查是哪種型別的時間,在此關注檢查讀事件
                {
					if(fd == sockfd)  //監聽套接字
					{  
						int len = sizeof(caddr);	
 
						int c = accept(sockfd,&caddr,&len);
						if(c <= 0)
						{
							continue;
						}
						
						printf("accept c=%d\n",c); 
           
						epoll_add(epfd,c);  //新的連線產生,新增到核心事件表中
				
					}
        
				    else  
				    {  
					  char buff[128] = {0};
					  int num = recv(fd,buff,1,0)
                      //每次讀一個字元,看LT模式下的執行規則
					  if( num <= 0)  //對方關閉
					  {  
                        //先epoll_del()移除再close()關閉,因為epoll_del()中epoll_ctl()這
                        //個系統呼叫要用到fd,所以不能先關閉,如果先關閉的話,就找不到了,在執
                        //行時會提示為無效描述符close()不會使值發生變化,但會使得值無效
						epoll_del(epfd,fd);
						close(fd);
						printf("one client close\n");
                        continue;
					  }  
					  printf("recv(%d):%s\n",fd,buff);  
					  send(fd,"OK",2,0);  
				   }
               }  
			}  
		}
	}  
}  
 

執行結果:

ET模式(高效模式):也叫邊沿觸發。描述符上有資料就緒,如果使用者把資料沒有處理或沒處理完,只提醒一次,下一輪I/O函式執行時不會提醒,除非有新資料到達。

ET模式下,一次將資料讀完的思路:

1、設定描述符為非阻塞

2、迴圈讀取

# include<stdio.h>
# include<sys/epoll.h>
# include<sys/socket.h>
# include<assert.h>
# include<arpa/inet.h>
# include<string.h>
# include<unistd.h>
# include<sys/socket.h>
# include<stdlib.h>
# include<errno.h>
# include<fcntl.h>
#define MAXFD 10

void setnonblock(int fd)//對檔案描述符設定非阻塞模式,防止迴圈式把自己阻塞住
{
	int oldfl = fcntl(fd, F_GETFL);//獲取原來的屬性資訊
	int newfl = oldfl | O_NONBLOCK;//加非阻塞屬性
	if(fcntl(fd, F_SETFL, newfl) == -1)
	{
		perror("fcntl error\n");
	}
}
void epoll_add(int epfd, int fd)
{
	struct epoll_event ev;
	ev.events = EPOLLIN|EPOLLET;
	ev.data.fd = fd;

	if(epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &ev) == -1)
	{
		perror("epoll ctl error");
	}
	setnonblock(fd);//在此呼叫設定非阻塞函式
}
void epoll_del(int epfd, int fd)
{
	if(epoll_ctl(epfd, EPOLL_CTL_DEL, fd, NULL) == -1)
	{
		perror("epoll ctl del error\n");
	}
}
int main()
{
	int sockfd = socket(AF_INET, SOCK_STREAM, 0);
	assert(sockfd != -1);

	struct sockaddr_in saddr, caddr;
	memset(&saddr, 0, sizeof(saddr));

	saddr.sin_family = AF_INET;
	saddr.sin_port = htons(6000);
	saddr.sin_addr.s_addr = inet_addr("127.0.0.1");

	int res = bind(sockfd, (struct sockaddr *)&saddr, sizeof(saddr));
	assert(res != -1);

	listen(sockfd, 5);

	int epfd = epoll_create(MAXFD);
	epoll_add(epfd, sockfd);
	struct epoll_event events[MAXFD];

	while(1)
	{
		printf("epoll_wait\n");
		int n = epoll_wait(epfd, events, MAXFD, 5000);
		if(n == -1)
		{
			printf("epoll_wait error\n");
			continue;
		}
		else if(n == 0)
		{
			printf("time out\n");
			continue;
		}
		else
		{
			int i = 0;
			for(; i < n; i++)
			{
				int fd = events[i].data.fd;
				if(events[i].events & EPOLLIN)
				{
					if(fd == sockfd)
					{
						int len = sizeof(caddr);
						int c = accept(sockfd, (struct sockaddr*)&caddr, &len);
						if( c < 0)
						{
							continue;
						}
						printf("accept c = %d\n", c);
						epoll_add(epfd, c);
					}
					else
					{
						while(1)
						{
							char buff[128] = {0};
							int num = recv(fd, buff, 1, 0);
							if(num == -1)//一波資料讀完了
							{
                                //出錯原因:由於沒資料出錯,EAGAIN 和 EWOULDBLOCK表示在非
                                //阻塞模式下,資料未準備好
								if(errno == EAGAIN || errno == EWOULDBLOCK)
								{
									send(fd, "ok", 2, 0);
								}
								break;
							}
							else if(num == 0)//對方關閉
							{
								epoll_del(epfd, fd);
								close(fd);
								printf("one client over\n");
								break;
							}
							printf("recv %d = %s\n",fd, buff);
						}
					}
				}
			}
		}
	}
}