tcp/ip 服务器 poll模型

上一节，学习了select模型的实现方式，本节学习poll是否方式，为接下来学习epoll模型作准备。很显然epoll是对poll方式的改进，先看poll是如何工作的。

/* include fig01 */
#include    "unp.h"
#include    <limits.h>        /* for OPEN_MAX */

int
main(int argc, char **argv)
{
    int                    i, maxi, listenfd, connfd, sockfd;
    int                    nready;
    ssize_t                n;
    char                buf[MAXLINE];
    socklen_t            clilen;
    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_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port        = htons(SERV_PORT);

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

    Listen(listenfd, LISTENQ);

    client[0].fd = listenfd;
    client[0].events = POLLRDNORM; //监听读事件
    for (i = 1; i < OPEN_MAX; i++)
        client[i].fd = -1;        /* -1 indicates available entry */
    maxi = 0;                    /* max index into client[] array */
/* end fig01 */

/* include fig02 */
    for ( ; ; ) {
        nready = Poll(client, maxi+1, INFTIM);

        if (client[0].revents & POLLRDNORM) {    /* 新的连接到来 */
            clilen = sizeof(cliaddr);
            connfd = Accept(listenfd, (SA *) &cliaddr, &clilen);
#ifdef    NOTDEF
            printf("new client: %s\n", Sock_ntop((SA *) &cliaddr, clilen));
#endif

            for (i = 1; i < OPEN_MAX; i++)
                if (client[i].fd < 0) {
                    client[i].fd = connfd;    /* 保存描述符到client数组中 */
                    break;
                }
            if (i == OPEN_MAX)
                err_quit("too many clients");

            client[i].events = POLLRDNORM; //设置为监听读事件
            if (i > maxi)
                maxi = i;                /* max index in client[] array */

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

        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) {
                            /*4connection reset by client */
#ifdef    NOTDEF
                        printf("client[%d] aborted connection\n", i);
#endif
                        Close(sockfd);
                        client[i].fd = -1;
                    } else
                        err_sys("read error");
                } else if (n == 0) {
                        /*4connection closed by client */
#ifdef    NOTDEF
                    printf("client[%d] closed connection\n", i);
#endif
                    Close(sockfd);
                    client[i].fd = -1;
                } else
                    Writen(sockfd, buf, n);

                if (--nready <= 0)
                    break;                /* no more readable descriptors */
            }
        }
    }
}
/* end fig02 */