epoll下电平触发LT和边沿触发ET的区别

本文主要是介绍epoll下电平触发LT和边沿触发ET的区别，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

LT 电平触发    高电平触发

EPOLLIN 事件  数据可读
内核中的socket接收缓冲区 为空  低电平  不会触发
内核中的socket接收缓冲区 不为空  高电平  会触发

EPOLLOUT事件 数据可写
内核中的socket发送缓冲区不满   高电平
内核中的socket发送缓冲区 满    低电平

ET 边沿触发  转换的时候触发
由低电平-》高电平  才会 触发
高电平-》低电平 触发

下面代码是LT和ET模式的区别

#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 MAX_EVENT_NUMBER 1024
#define BUFFER_SIZE 10int 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 );}else if ( events[i].events & EPOLLIN ){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, true );}else if ( events[i].events & EPOLLIN ){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[] )
{if( argc <= 2 ){printf( "usage: %s ip_address port_number\n", basename( 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( 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 failure\n" );break;}lt( events, ret, epollfd, listenfd );//et( events, ret, epollfd, listenfd );}close( listenfd );return 0;
}

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