epoll 中ET与LT 关于读取处理 复习

https://zhuanlan.zhihu.com/p/21374980

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https://zhuanlan.zhihu.com/p/21619218?utm_medium=social&utm_source=wechat_session&from=timeline&isappinstalled=0&s_s_i=akD%2BEQGuE2ymUvWOlk%2BEkZpTXXDTr7pm24gvEBEAW%2Fg%3D&s_r=1

EPOLL事件的两种模型：

Level Triggered (LT) 水平触发
.socket接收缓冲区不为空 有数据可读 读事件一直触发
.socket发送缓冲区不满 可以继续写入数据 写事件一直触发
符合思维习惯，epoll_wait返回的事件就是socket的状态

关键是ET模型这里写的很好了   仔细体会 以后不会再复习了 

Edge Triggered (ET) 边沿触发   
.socket的接收缓冲区状态变化时触发读事件，即空的接收缓冲区  刚接收到数据时触发读事件
.socket的发送缓冲区状态变化时触发写事件，即满的缓冲区  刚空出空间时触发读事件
仅在状态变化时触发事件

https://blog.csdn.net/linuxheik/article/details/73294658

这个文章写的也可以但是 没有上面的到位

由上面的情况可以看出 LE模式来数据时候 缓冲区不完全读取结束没有事情  下次该事件他还会继续触发     但是ET  （默认就是非阻塞情况哦  ）则不行      必须 将缓冲区读取结束，读到EAGAIN | EWOULDBLOCK且 n  < 0   这样该socket连接的缓冲区 下次发生事件（即有数据）时候才会再次触发。 

ET 模型 LT 模型的处理方式代码

#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 MAX_EVENT_NUMBER 1024
#define BUFFER_SIZE 10

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 );
        }
        else if ( events[i].events & EPOLLIN )
        {//只要socket读缓存区中还有未读出的数据  这段代码就会不停的被触发 即使关闭了sock
            printf( "event trigger once
" );
            memset( buf, '', BUFFER_SIZE );
            int ret = recv( sockfd, buf, BUFFER_SIZE-1, 0 );
            if( ret <= 0 )
            {
                close( sockfd );
                continue;
            }
            printf( "get %d bytes of content: %s
", ret, buf );
        }
        else
        {
            printf( "something else happened 
" );
        }
    }
}

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 )
        {    //for 循环到某个sock连接的缓存区有数据 可读那么就要 while读取读到缓存区没有数据 ET模式
			//确保把socket缓冲区存储的数据读取结束  才break 退出while
            printf( "event trigger once
" );
            while( 1 )
            {
                memset( buf, '', BUFFER_SIZE );
                int ret = recv( sockfd, buf, BUFFER_SIZE-1, 0 );
                if( ret < 0 )
                {//非阻塞ET模式 下面成立表示sock缓冲区数据读取结束了   此后epoll_wait就能再次触发,就能再一次触发fd 上的EPOLLIN事件
                    if( ( errno == EAGAIN ) || ( errno == EWOULDBLOCK ) )
                    { //无需关闭socket  只说明现在缓冲区没有数据可以读取了  等待下一次触发处理
                        printf( "read later
" );
                        break;//这里 缓冲区数据读取over了  所以break掉当前读取sock的while循环
                    }
					//返回-1 那么说明发生其他错误不是上面的两种错误直接关闭sock
                    close( sockfd );
                    break;
                }
                else if( ret == 0 )
                {                                                           
                    close( sockfd );// ==0 ET模式返回0 表示对端已经关闭了
                }
                else
                {   //接收ok
                    printf( "get %d bytes of content: %s
", ret, buf );
                }
            }
        }
        else
        {
            printf( "something else happened 
" );
        }
    }
}

int main( int argc, char* argv[] )
{
    if( argc <= 2 )
    {
        printf( "usage: %s ip_address port_number
", 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
" );
            break;
        }
    
        //lt( events, ret, epollfd, listenfd );
        et( events, ret, epollfd, listenfd );
    }

    close( listenfd );
    return 0;
}

　　

和上面不相关

void handleRead(int efd, int fd) {
    char buf[4096];
    int n = 0;
    while ((n=::read(fd, buf, sizeof buf)) > 0) {
        if(output_log) printf("read %d bytes
", n);
        string& readed = cons[fd].readed;
        readed.append(buf, n);
        if (readed.length()>4) {
            if (readed.substr(readed.length()-2, 2) == "

" || readed.substr(readed.length()-4, 4) == "

") {
                //当读取到一个完整的http请求，测试发送响应
                sendRes(fd);
            }
        }
    }
//这里当socket缓冲区的数据被读取完毕了，return掉  但不能close fd  因为下次该sock缓冲区有数据还会再次触发
//ET 非阻塞就是要读到 EAGAIN 且 n < 0 就是将来sock缓冲区读彻底下次才触发
    if (n<0 && (errno == EAGAIN || errno == EWOULDBLOCK))
        return;
    //实际应用中，n<0应当检查各类错误，如EINTR
    if (n < 0) {
        printf("read %d error: %d %s
", fd, errno, strerror(errno));
    }
    close(fd);
    cons.erase(fd);
}