常见指令：telent 127.0.0.1 8080 连接

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     service iptables stop 关闭防火墙

在TCP连接中，主动关闭连接的一方会进入2MSL,如果是服务器端，当TIME_WAIT时，sock不能被复用（四次挥手），使用setsockopt解决。

int opt=1;

setsockopt(listenfd,SOL_SOCKET,SO_REUSEADDR,&opt,sizeof(opt));

epoll是linux内核为处理大批量文件描述符而作了改进的poll，是Linux下多路复用IO接口select/poll的增强版本，它能显著提高程序在大量并发连接中只有少量活跃的情况下的系统CPU利用率。另一点原因就是获取事件的时候，它无须遍历整个被侦听的描述符集，只要遍历那些被内核IO事件异步唤醒而加入Ready队列的描述符集合就行了。

注：epoll除了提供select/poll那种IO事件的水平触发（Level Triggered）外，还提供了边缘触发（Edge Triggered），这就使得用户空间程序有可能缓存IO状态，减少epoll_wait/epoll_pwait的调用，提高应用程序效率。

注：epoll文件描述符用完后，直接用close关闭即可，非常方便。事实上，任何被侦听的文件符只要其被关闭，那么它也会自动从被侦听的文件描述符集合中删除，很是智能。

epoll相关的系统调用有：epoll_create, epoll_ctl和epoll_wait。

1.epoll_create用来创建一个epoll文件描述符。

返回值:

>0：非空文件描述符；

-1：函数调用失败，同时会自动设置全局变量errno；

2.epoll_ctl用来添加/修改/删除需要侦听的文件描述符及其事件.

epoll的事件注册函数，它不同于select()是在监听事件时告诉内核要监听什么类型的事件，而是在这里先注册要监听的事件类型。

epfd:epoll_create的返回值

op:表示动作，为以下三个宏任意一个（根据需要）：添加，修改，删除

fd:为关心的描述符

event为：关心描述符事件

返回值：成功，返回0；失败，返回-1，置错误码。

3.epoll_wait/epoll_pwait接收发生在被侦听的描述符上的，用户感兴趣的IO事件。

收集在epoll监控的事件中已经就绪的事件。

events：是分配好的epoll_event结构体数组，epoll将会把就绪的事件赋值到events数组中（events不可以是空指针，内核只负责把数据复制到这个events数组中）。

maxevents：告之内核这个events有多大，这个 maxevents的值不能小于创建epoll_create()时的size

timeout：是超时时间（毫秒）

    1.0表示轮询非阻塞，立即返回；

    2.-1将不确定，也有说法说是永久阻塞。

    3.大于0，以timeput事件轮询返回

返回值：

    1.成功，返回对应I/O上已准备好的文件描述符数

    2.0表示已超时。

    3.-1，发生错误。

//初级版
#include                                                               
#include
#include
#include
#include
#include
#include
#include
#include
#define _SIZE_ 64
#define _BACKLOG_ 5
typedef struct fdBuf
{
    void * _buf;
    int _fd;
}fdBuf;
static void usage(const char* proc)
{
    printf("%s [ip][port]",proc);
}
static int startup(char* ip,int port)
{
    int listen_sock=socket(AF_INET,SOCK_STREAM,0);
    if(listen_sock<0)
    {
        perror("socket");
        exit(1);
    }
    struct sockaddr_in local;
    local.sin_family=AF_INET;
    local.sin_port=htons(port);
    local.sin_addr.s_addr=inet_addr(ip);
    if(bind(listen_sock,(struct sockaddr*)&local,sizeof(local))<0)
    {
        perror("bind");
        exit(2);
    }
    if(listen(listen_sock,_BACKLOG_)<0)
    {
        perror("listen");
        exit(3);
    }
    return listen_sock;
}
int sock_epoll(int listen_sock)
{   
    //1.create fds instance
    int  ins=epoll_create(_SIZE_);
    if(ins<0)
    {
        perror("poll_create");
        return 1;
    }
    struct epoll_event ev;
    ev.events=EPOLLIN;
    ev.data.fd=listen_sock;
    int i=0;//index
    fdBuf bufs[_SIZE_];
    for(i=0;i<_SIZE_;++i)
    {
        bufs[i]._fd=-1;
        bufs[i]._buf=NULL;
    }
    struct epoll_event fds[_SIZE_];//with bufs save buf 
    for(i=0;i<_SIZE_;++i)
    {
        fds[i].events=0;
        fds[i].data.fd=-1;
    }                                             
    epoll_ctl(ins,EPOLL_CTL_ADD,listen_sock,&ev);
    int ret=-1;
    int timeout=5000;
    struct sockaddr_in remote;
    socklen_t len=sizeof(remote);
    ssize_t _s;//charnum
    while(1)
    {
        switch((ret=epoll_wait(ins,fds,64,timeout)))
        {
            case -1://error
                perror("epoll_wait");
                break;
            case 0://time out
                printf("time is out\n");
                break;
            default:
                {
                    for(i=0;i0&&fds[i].events&EPOLLIN)
                        {
                            if(bufs[i]._fd==-1)
                            {
                                char *buf=(char*)malloc(sizeof(char)*1024);
                                bufs[i]._fd=fds[i].data.fd;
                                bufs[i]._buf=buf;                    
                            }
                            //save buf and fd
                            memset(bufs[i]._buf,'\0',1024);
                            //sleep(1);
                            fflush(stdout);
                            _s=read(fds[i].data.fd,bufs[i]._buf,sizeof(bufs[i]._buf)-1);
                            if(_s>0)
                            {
                                ((char*)bufs[i]._buf)[_s]='\0';
                                printf("client:%s",(char*)bufs[i]._buf);//输出
                                ev.events=EPOLLOUT;
                                ev.data.fd=fds[i].data.fd;
                                epoll_ctl(ins,EPOLL_CTL_MOD,fds[i].data.fd,&ev);
                            }
                            else if(_s==0)
                            {
                                printf("client is close...\n");
                                free(bufs[i]._buf);
                                bufs[i]._fd=-1;
                                bufs[i]._buf=NULL;
                                //remove
                                epoll_ctl(ins,EPOLL_CTL_DEL,fds[i].data.fd,NULL);  
                            }     
                            else
                            {}
                        }
                        else if(fds[i].data.fd>0&&fds[i].events&EPOLLOUT)
                        {
                            write(fds[i].data.fd,bufs[i]._buf,strlen(bufs[i]._buf));
                            ev.events=EPOLLIN;
                            ev.data.fd=fds[i].data.fd;
                            epoll_ctl(ins,EPOLL_CTL_MOD,fds[i].data.fd,&ev);
                        }
                        else
                        {}
                    }
                break;
                }//default end
        }//switch end
    }//while end
}
int main(int argc,char* argv[])
{
    if(argc!=3)
    {
        usage(argv[0]);                                                 
        return 1;
    }
    int _port=atoi(argv[2]);
    char* _ip=argv[1];
    int listen_sock=startup(_ip,_port);
    sock_epoll(listen_sock);
    close(listen_sock);
    return 0;
}                                                                                        
//client                                                               
#include                                                                        
#include
#include
#include
#include
#include
#include
#include
static void usage(const char* proc)
{
    printf("%s [i][port]",proc);
}
int main(int argc,char* argv[])
{
    if(argc!=3)
    {
        usage(argv[0]);
        return 1;
    }
    int sock=socket(AF_INET,SOCK_STREAM,0);
    if(sock<0)
    {
        perror("socket");
        return 2;
    }
    struct sockaddr_in local;
    local.sin_family=AF_INET;
    local.sin_port=htons(atoi(argv[2]));
    local.sin_addr.s_addr=inet_addr(argv[1]);
    if(connect(sock,(struct sockaddr*)&local,sizeof(local))<0)
    {
        perror("connect");
        return 3;
    }
    char buf[1024];
    ssize_t _s;
    while(1)
    {
        printf("please input\n");
        fflush(stdout);
        _s=read(0,buf,sizeof(buf)-1);
        if(_s>0)
        {
            buf[_s]='\0';
            if(strncmp(buf,"quit",4)==0)
            {                                           
                close(sock);
                return 0;
            }
            write(sock,buf,strlen(buf));
        }
        else if(_s==0)
        {
            close(sock);
            return 1;
        }
        _s=read(sock,buf,sizeof(buf)-1);
        if(_s>0)
        {
            buf[_s]='\0';
            printf("echo:%s\n",buf);
        }
    }
    return 0;
}

运行截图：

client:

server:

//server_epoll
#include                                                                        
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define _MAX_FD_NUM_  64
typedef struct _fd_buf
{
    int fd;
    char buf[1024];
}fdBuf_t,*fdBuf_p;
static void usage(const char* const proc)
{
    assert(proc);
    printf("usage:%s[ip][port]",proc);
}
static int start(char* ip,int port)
{
    assert(ip);
    int sock=socket(AF_INET,SOCK_STREAM,0);
    if(sock<0)
    {
        perror("socket");
        exit(1);
    }
    struct sockaddr_in local;
    local.sin_family=AF_INET;
    local.sin_port=htons(port);
    local.sin_addr.s_addr=inet_addr(ip);
    //reuse socket
    int opt=1;
    setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&opt,sizeof(opt));
    if(bind(sock,(struct sockaddr*)&local,sizeof(local))<0)
    {
        perror("bind");
        exit(2);
    }
    if(listen(sock,5)<0)
    {
        perror("listen");
        exit(3);                  
    }
    return sock;
}
static int epoll_server(int sock)
{
    int epoll_fd=epoll_create(256);//-1 or fd
    if(epoll_fd<0)
    {
        perror("epoll_create");
        return -1;
    }
    struct epoll_event ev;
    ev.events=EPOLLIN;
    ev.data.fd=sock;
    //0 success or -1 fail
    if(epoll_ctl(epoll_fd,EPOLL_CTL_ADD,sock,&ev)<0)
    {
        perror("epoll_ctl");
        return -1;
    }
    struct epoll_event fds[_MAX_FD_NUM_];
    int ret=-1;
    int timeout=5000;                      
    int i=0;
    struct sockaddr_in client;
    socklen_t len=sizeof(client);
    ssize_t _s=-1;
    while(1)
    {
        switch((ret=epoll_wait(epoll_fd,fds,_MAX_FD_NUM_,timeout)))
        {
            case -1://error
                perror("epoll_wait");
                break;
            case 0:
                printf("time out...\n");
                break;
            default:
                {
                    for(i=0;ibuf,sizeof(mem->buf)-1);
                                if(_s>0)
                                {
                                    mem->fd=fds[i].data.fd;
                                    (mem->buf)[_s]='\0';
                                    fds[i].data.ptr=mem;
                                    printf("client:%s",mem->buf);
                                    ev.events=EPOLLOUT;
                                    ev.data.ptr=mem;           
                                    epoll_ctl(epoll_fd,EPOLL_CTL_MOD,mem->fd,&ev);
                                }
                                else if(_s==0)
                                {
                                    free(mem);
                                    close(fds[i].data.fd);
                                    continue;
                                    epoll_ctl(epoll_fd,EPOLL_CTL_DEL,fds[i].data.fd,NULL);
                                }
                                else
                                {}

                            }
                            else if(fds[i].events&EPOLLOUT)
                            {
                                fdBuf_p cur=(fdBuf_p)fds[i].data.ptr;
                                write(cur->fd,cur->buf,strlen(cur->buf));
                                close(cur->fd);
                                epoll_ctl(epoll_fd,EPOLL_CTL_DEL,cur->fd,NULL);
                                free(cur);
                            }
                            else{}                    
                        }
                    }
                }
                break;
        }
    }
}
int main(int argc,char* argv[])
{
    if(argc!=3)
    {
        usage(argv[0]);
        return -1;
    }
    char* ip=argv[1];
    int port=atoi(argv[2]);
    int listen_sock=start(ip,port);
    epoll_server(listen_sock);
    close(listen_sock);
    return 0;
}

运行截图：浏览器访问，

请求行---响应行

client用的什么方法，什么浏览器（火狐），协议版本http/1.0 + 状态 200成功+错误码（eg:400页面不存在）

改为显示hello的：

修改代码：

LT(level triggered)是epoll缺省的工作方式，并且同时支持block和no-block socket.在这种做法中，内核告诉你一个文件描述符是否就绪了，然后你可以对这个就绪的fd进行IO操作。如果你不作任何操作，内核还是会继续通知你的，所以，这种模式编程出错误可能性要小一点。传统的select/poll都是这种模型的代表．

下来修改epoll为ET触发。

先修改文件描述符为非阻塞

#include                                                               
#include
#include
#include
#include
#include
static void setnoblock(int fd)
{
    //get flag
    int fl=fcntl(fd,F_GETFL);//arg is ignore
    if(fl<0)
    {
        perror("fcntl");
        exit(1);
    }
    //set flag
    if(fcntl(fd,F_SETFL,fl|O_NONBLOCK))//isn't 0 is error
    {
        perror("fcntl");
        exit(1);
    }
}
int main()
{                                                                               
    setnoblock(0);
    char buf[20];
    ssize_t _s=-1;
    while(1)
    {
        memset(buf,'\0',20);
        _s=read(0,buf,sizeof(buf)-1);
        if(_s>0)
        {
            buf[_s]='\0';
            printf("echo:%s",buf);
        }
        else if(_s==0)
        {
            //do nothing
        }
        else
        {
            if(errno==EAGAIN)//EAGAIN==11
            {
                printf("no data\n");
            }
        }
        sleep(1);
    }
    return 0;
}

修改epoll为ET

//read
static int readData(int sock,char* buf,int size)
{
    assert(buf);
    memset(buf,'\0',size);
    int i=0;
    int ret=-1;
    while((ret=read(sock,buf+i,size-i))
epoll:ET，非阻塞代码
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define _MAX_FD_NUM_  64
typedef struct _fd_buf
{
    int fd;
    char buf[1024];
}fdBuf_t,*fdBuf_p;
static void setnoblock(int fd)
{
    int fl=fcntl(fd,F_GETFL);
    if(fl<0)
    {
        perror("fcntl");
        exit(1);
    }
    if(fcntl(fd,F_SETFL,fl|O_NONBLOCK))
    {
        perror("fcntl");
        exit(1);
    }
}
static void usage(const char* const proc)
{
    assert(proc);
    printf("usage:%s[ip][port]",proc);
}
static int start(char* ip,int port)
{
    assert(ip);
    int sock=socket(AF_INET,SOCK_STREAM,0);
    if(sock<0)
    {
        perror("socket");
        exit(1);
    }
    struct sockaddr_in local;
    local.sin_family=AF_INET;
    local.sin_port=htons(port);
    local.sin_addr.s_addr=inet_addr(ip);
    //reuse socket
    int opt=1;
    setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&opt,sizeof(opt));
    if(bind(sock,(struct sockaddr*)&local,sizeof(local))<0)
    {
        perror("bind");
        exit(2);
    }
    if(listen(sock,5)<0)
    {
        perror("listen");
        exit(3);
    }
    return sock;
}
//read
static int readData(int sock,char* buf,int size)
{
    assert(buf);
    memset(buf,'\0',size);
    int i=0;
    int ret=-1;
    while((ret=read(sock,buf+i,size-i))buf,sizeof(mem->buf)-1);
                                _s=readData(fds[i].data.fd,mem->buf,sizeof(mem->buf));
                                if(_s>0)
                                {
                                    mem->fd=fds[i].data.fd;
                                    (mem->buf)[_s]='\0';
                                    fds[i].data.ptr=mem;
                                    printf("client:%s",mem->buf);
                                    ev.events=EPOLLOUT|EPOLLET;
                                    ev.data.ptr=mem;
                                    epoll_ctl(epoll_fd,EPOLL_CTL_MOD,mem->fd,&ev);
                                }
                                else if(_s==0)
                                {
                                    free(mem);
                                    close(fds[i].data.fd);
                                    continue;
                                    epoll_ctl(epoll_fd,EPOLL_CTL_DEL,fds[i].data.fd,NULL);
                                }
                     &nb            
            
                            

                文章题目：epoll实现TCP通信                

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