man poll:

NAME

poll, ppoll - wait for some event on a file descriptor

SYNOPSIS

#include <poll.h>

int poll(struct pollfd *fds, nfds_t nfds, int timeout);

#define _GNU_SOURCE /* See feature_test_macros(7) */

#include <poll.h>

int ppoll(struct pollfd *fds, nfds_t nfds,

const struct timespec *timeout_ts, const sigset_t *sigmask);

DESCRIPTION

poll() performs a similar task to select(2): it waits for one of a set of file descriptors to become ready to per‐

form I/O.

The set of file descriptors to be monitored is specified in the fds argument, which is an array of structures of the

following form:

struct pollfd {

int fd; /* file descriptor */

short events; /* requested events */

short revents; /* returned events */

};

要测试的条件由events指定，函数在相应的revents成员中返回该描述字的状态。（每个描述字都有两个变量，一个为调用值，另一个为返回结果，从而避免使用值结果参数。）

结果数组中元素的个数由nfds参数指定。

返回值：当发生错误时，poll函数的返回值为-1，若定时器时间到之前没有任何描述字就绪，则返回0.否则返回就绪描述字的个数，即其revents成员值非0的描述字个数。

如果我们不再关心某个特定描述字，那么可以把与它对应的pollfd结构的fd成员设置为一个负值。poll函数将忽略这样的pollfd结构的events成员，返回时将它的revents成员的值置为0.

 

　　020.#ifndef INFTIM     /*按照书上解释：POSIX规范要求INFTIM在头文件<poll.h>中定义，不过*/

　　021.#define INFTIM -1  /*许多系统仍然把它定义在头文件<sys/stropts.h>中，但是经过我的测试*/

　　022.#endif             /*即使都包含这两个文件，编译器也找不到，不知何解。索性自己定义了。*/

 



#include"unp.h"
#include<limits.h>//for open_MAX,ubuntuۃбûԐ
#define OPEN_MAX 1024
#define INFTIM -1

int main(int argc,char **argv)
{
    int i ,maxi,listenfd,connfd,sockfd;
    int nready;
    ssize_t n;

    socklen_t clilen;
    char buf[MAXLINE];

    struct pollfd client[OPEN_MAX];
    struct sockaddr_in cliaddr,servaddr;
    listenfd=Socket(AF_INET,SOCK_STREAM,0);
    bzero(&servaddr,sizeof(servaddr));
    servaddr.sin_family=AF_INET;
    servaddr.sin_port=htons(8001);
    servaddr.sin_addr.s_addr=htonl(INADDR_ANY);

    Bind(listenfd,(SA*)&servaddr,sizeof(servaddr));
    Listen(listenfd,LISTENQ);

    client[0].fd=listenfd;
    client[0].events=POLLRDNORM;
    for(i=1;i<OPEN_MAX;i++)
        client[i].fd=-1;// 
    maxi=0;

    for(;;)
    {
        nready=poll(client,maxi+1,INFTIM);
        if(client[0].revents  & POLLRDNORM ) 
        { //new client connction
            clilen=sizeof(cliaddr);
            connfd=Accept(listenfd,(SA*)&cliaddr,&clilen);

            for(i=1;i<OPEN_MAX;i++)
            {
                if(client[i].fd<0)
                {
                    client[i].fd=connfd;//save desc
                    break;
                }
            }
            if(i==OPEN_MAX)
                err_quit("too many client");
            client[i].events=POLLRDNORM;
            if(i>maxi)
                maxi=i;
            if(--nready<=0)
                continue;
        }
        for(i=1;i<=maxi;i++)
        {
            //check all clients for data
            if( (sockfd=client[i].fd)<0)
                continue;
            if(client[i].revents & ( POLLRDNORM | POLLERR))
            {
                if((n=read(sockfd,buf,MAXLINE))<0)
                {
                    if(errno==ECONNRESET)
                    {
                        //conncetion reset by client
                        Close(sockfd);
                        client[i].fd=-1;
                    }
                    else
                        err_sys("read error");
                }
                else if(n==0)
                {
                    //connection close by client
                    Close(sockfd);
                    client[i].fd=-1;
                }
                else    Writen(sockfd,buf,n);

               if(--nready<=0)
                    break;
            }
        }
    }
}