UNIX网络编程学习（15）--使用单进程和select的TCP服务器程序

#include	"unp.h"

int
main(int argc, char ** argv)
{
    int         i,maxi,maxfd,listenfd,connfd,sockfd;
    int         nready,client[FD_SETSIZE];
    ssize_t     n;
    fd_set      rset,allset;
    char        buf[MAXLINE];
    socklen_t   clilen;
    struct      sockaddr_in cliaddr,servaddr;

    listenfd = Socket(AF_INET, SOCK_STREAM, 0);

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(SERV_PORT);//#define	SERV_PORT		 9877
    Bind(listenfd, (SA *)&servaddr, sizeof(servaddr));
    Listen(listenfd, LISTENQ);

    maxfd = listenfd;/* initialize */
    printf("listenfd=%d\n",maxfd);//listenfd=3
    maxi = -1;/* index into client[] array */
    for(i = 0;i<FD_SETSIZE;i++)//FD_SETSIZE is 1024
        client[i]=-1;/* -1 indicates available entry */
    FD_ZERO(&allset);
    FD_SET(listenfd,&allset);

    for( ; ; )
    {
        rset = allset;//structure assignment
        nready = Select(maxfd+1,&rset,NULL,NULL,NULL);

        if(FD_ISSET(listenfd,&rset))/* new client connection */
        {
            clilen = sizeof(cliaddr);
            connfd = Accept(listenfd ,(SA *)&cliaddr,&clilen);

            for(i=0;i<FD_SETSIZE;i++)
            {
                client[i]=connfd;//save descriptor
                break;
            }
            if(i==FD_SETSIZE)
                err_quit("too many clients");

            FD_SET(connfd,&allset);//add new descriptor to set
            if(connfd > maxfd)
                maxfd = connfd;/* for select */
            if(i > maxi)
                maxi = i;/* max index in client[] array */
            if(--nready <= 0)
                continue;/* no more readable descriptors */
        }

        for(i=0;i<=maxi;i++)/* check all clients for data */
        {
            if((sockfd = client[i])<0)
                continue;
            if(FD_ISSET(sockfd,&rset))
            {
                if((n = Read(sockfd,buf,MAXLINE)) == 0)/*connection closed by client */
                {
                    Close(sockfd);
                    FD_CLR(sockfd,&allset);
                    client[i]=-1;
                }
                else
                    Writen(sockfd,buf,n);

                if(--nready <= 0)
                    break;/* no more readable descriptors */
            }
        }
    }
}