最簡單的socket通訊端編程(2)–poll()和epoll()

最簡單的socket通訊端編程(2)–poll()和epoll()

作者：gaopenghigh ，轉載請註明出處。 （原文地址）

本文主要介紹了使用poll()和epoll()在UNIX環境下socket網路編程的主要步驟，實現 了一個簡單的 伺服器和用戶端代碼執行個體，實現了一個網路服務，該服務接受一個字串的命令，執行該命 令，並且把結 果返回給用戶端。

關於socket網路編程的基本概念以及多進程、多線程的網路伺服器的原理和執行個體，參考 最簡單的socket通訊端編程。

關於poll()和epoll()的介紹和用法，參考 一步步理解Linux之IO（2）–進階IO

Client

#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <string.h>#include <sys/types.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h>#include <netdb.h>#define BUFLEN 256void error(const char *msg){    perror(msg);    exit(0);}int main(int argc, char *argv[]){    int sockfd, portno, n;    struct sockaddr_in serv_addr;    struct hostent *server;    char buffer[BUFLEN];    if (argc < 3) {       fprintf(stderr,"usage %s hostname port\n", argv[0]);       exit(0);    }    portno = atoi(argv[2]);    if ((server = gethostbyname(argv[1])) == NULL) {        fprintf(stderr,"ERROR, no such host\n");        exit(0);    }    bzero((char *) &serv_addr, sizeof(serv_addr));    serv_addr.sin_family = AF_INET;    bcopy((char *)server->h_addr,          (char *)&serv_addr.sin_addr.s_addr,          server->h_length);    serv_addr.sin_port = htons(portno);    while (1) {        if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)            error("ERROR opening socket");        if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)            error("ERROR connecting");        printf(">>> ");        bzero(buffer, BUFLEN);        fgets(buffer, BUFLEN, stdin);        if((n = send(sockfd, buffer, strlen(buffer), 0)) <= 0)             error("ERROR writing to socket");        bzero(buffer, BUFLEN);        while ((n = recv(sockfd, buffer, BUFLEN, 0)) > 0) {            printf("%s",buffer);        }    }    return 0;}

poll()實現的server

/* A simple server to run system commands use poll */#include <stdio.h>#include <stdlib.h>#include <string.h>#include <signal.h>#include <unistd.h>#include <sys/types.h>#include <sys/socket.h>#include <netinet/in.h>#include <poll.h>#include <fcntl.h>#define PORTNO 4444#define BACKLOG 10#define BUFLEN 256#define MAXCONN 100#define TRUE 1#define FALSE 0void error(const char *msg) {    perror(msg);}/* * function really do the service * run cmd geted from client and return the output to client */void serve(struct pollfd *pfd) {    int n;    char buffer[BUFLEN];    FILE *fp;    bzero(buffer, BUFLEN);    printf("in serve ,fd=%d\n", pfd->fd);    if (pfd->revents & POLLIN) {                /* read */        if ((n = read(pfd->fd, buffer, BUFLEN)) < 0)            printf("ERROR reading from socket : %d", n);        printf("CMD : %s\n",buffer);        if ((fp = popen(buffer, "r")) == NULL)            error("ERROR when popen");        while (fgets(buffer, BUFLEN, fp) != NULL) {            if (send(pfd->fd, buffer, BUFLEN, 0) == -1)                error("send ERROR");        }        printf("serve end, closing %d\n", pfd->fd);        close(pfd->fd);        pfd->fd = -1;        pclose(fp);    }}/* * Init listen socket and bind it to addr, return the listen socket */int init_server() {    int sockfd;    struct sockaddr_in serv_addr;    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {        error("ERROR opening socket");        exit(1);    }    bzero((char *) &serv_addr, sizeof(serv_addr));    serv_addr.sin_family = AF_INET;    serv_addr.sin_addr.s_addr = INADDR_ANY;    serv_addr.sin_port = htons(PORTNO);    if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) {        error("ERROR on binding");        exit(1);    }    return sockfd;}/* * set fd nonblocking, success return 0, fail return -1 */int setnonblocking(int fd) {    if (fd > 0) {        int flags = fcntl(fd, F_GETFL, 0);        flags = flags|O_NONBLOCK;        if (fcntl(fd, F_SETFL, flags) == 0) {            printf("setnonblocking success!\n");            return 0;        }    }    return -1;}void printfd(struct pollfd array[], int n) {    int i;    printf("array = ");    for(i = 0; i < n; i++)        printf("[%d]:%d ", i, array[i].fd);    printf("\n");}/* * Use poll() to serve for every connection */int main(int argc, char *argv[]) {    int endserver = FALSE;    int listen_sock, conn_sock, pos, i, j;    struct sockaddr_in cli_addr;    socklen_t clilen = sizeof(cli_addr);    /* INIT pollfd structures */    struct pollfd allfds[MAXCONN];    printf("sizeof(allfds)=%d\n", (int)sizeof(allfds));    memset(allfds, 0, sizeof(allfds));    int nfds = 0;    /* number of fds in allfds */    int currentsize; /* current size of allfds */    int poll_result;    /* init listen socket, bind, listen */    listen_sock = init_server();    setnonblocking(listen_sock);    listen(listen_sock, BACKLOG);    /* add listen_socket to allfds array */    allfds[0].fd = listen_sock;    allfds[0].events = POLLIN;    nfds++;    while (endserver == FALSE) {        printfd(allfds, nfds);        printf("nfds=%d\n", nfds);        /* wait for events on sockets, timeout = -1 means waite forever */        poll_result = poll(allfds, nfds, -1);        if (poll_result == -1) {            error("poll ERROR");            break;        } else if (poll_result == 0) {            printf("poll round timeout, enther another poll...\n");            continue;        }        /*******************************************************************/        /* One or more descriptors are readable                            */        /*******************************************************************/        currentsize = nfds;        printf("correntsize=%d\n", currentsize);        for (pos = 0; pos < currentsize; pos++) {            if (allfds[pos].revents & POLLIN &&                    allfds[pos].fd == listen_sock) {  /* listen socket */                printf("event on listen sock\n");                /* Accept all incomming connections */                do {                    printf("listen_sock=%d\n", listen_sock);                    conn_sock = accept(listen_sock,                                   (struct sockaddr *)&cli_addr, &clilen);                    if (conn_sock < 0)                        continue;                    setnonblocking(conn_sock);                    if (nfds >= MAXCONN) {                        error("nfds >= MAXCONN");                        break;                    }                    allfds[nfds].fd = conn_sock;                    allfds[nfds].events = POLLIN;                    nfds++;                } while(conn_sock != -1);            /* regular socket */            } else {                serve(&allfds[pos]);            }            /* comparess allfds, delete the items which fd = -1 */            for (i = 0; i < nfds; i++) {                if (allfds[i].fd == -1) {                    for (j = i; j < nfds; j++) {                        allfds[j] = allfds[j+1];                    }                    nfds--;                    i--;                }            }        }    }    /* end server */    for (i = 0; i < nfds; i++) {        if (allfds[i].fd >= 0)            close(allfds[i].fd);    }    return 0;}

epoll()實現的server

/* A simple server to run system commands use poll */#include <stdio.h>#include <stdlib.h>#include <string.h>#include <signal.h>#include <unistd.h>#include <sys/types.h>#include <sys/socket.h>#include <netinet/in.h>#include <sys/epoll.h>#include <fcntl.h>#define PORTNO 4444#define BACKLOG 10#define BUFLEN 256#define MAXCONN 100#define TRUE 1#define FALSE 0void error(const char *msg) {    perror(msg);}/* * function really do the service * run cmd geted from client and return the output to client */void serve(int fd) {    int n;    char buffer[BUFLEN];    FILE *fp;    bzero(buffer, BUFLEN);    printf("in serve ,fd=%d\n", fd);    if ((n = read(fd, buffer, BUFLEN)) < 0)        printf("ERROR reading from socket : %d", n);    printf("CMD : %s\n",buffer);    if ((fp = popen(buffer, "r")) == NULL)        error("ERROR when popen");    while (fgets(buffer, BUFLEN, fp) != NULL) {        if (send(fd, buffer, BUFLEN, 0) == -1)            error("send ERROR");    }    printf("serve end, closing %d\n", fd);    pclose(fp);}/* * Init listen socket and bind it to addr, return the listen socket */int init_server() {    int sockfd;    struct sockaddr_in serv_addr;    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {        error("ERROR opening socket");        exit(1);    }    bzero((char *) &serv_addr, sizeof(serv_addr));    serv_addr.sin_family = AF_INET;    serv_addr.sin_addr.s_addr = INADDR_ANY;    serv_addr.sin_port = htons(PORTNO);    if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) {        error("ERROR on binding");        exit(1);    }    return sockfd;}/* * set fd nonblocking, success return 0, fail return -1 */int setnonblocking(int fd) {    if (fd > 0) {        int flags = fcntl(fd, F_GETFL, 0);        flags = flags|O_NONBLOCK;        if (fcntl(fd, F_SETFL, flags) == 0) {            printf("setnonblocking success!\n");            return 0;        }    }    return -1;}/* * Use poll() to serve for every connection */int main(int argc, char *argv[]) {    int endserver = FALSE;    int listen_sock, conn_sock, n;    struct sockaddr_in cli_addr;    socklen_t clilen = sizeof(cli_addr);    /* INIT pollfd structures */    struct epoll_event ev, events[MAXCONN];    int nfds;    int epollfd = epoll_create(10);    if (epollfd == -1) {        printf("epoll_create error\n");        exit(1);    }    /* init listen socket, bind, listen */    listen_sock = init_server();    setnonblocking(listen_sock);    listen(listen_sock, BACKLOG);    /* register listen_sock to epollfd */    ev.events = EPOLLIN;    ev.data.fd = listen_sock;    if (epoll_ctl(epollfd, EPOLL_CTL_ADD, listen_sock, &ev) == -1) {        printf("ERROR: epoll_ctl\n");        exit(1);    }    while (endserver == FALSE) {        nfds = epoll_wait(epollfd, events, MAXCONN, -1);        if (nfds == -1) {            printf("epoll_wait ERROR\n");            exit(1);        }        for (n = 0; n < nfds; n++) {            if (events[n].data.fd == listen_sock) { /* listen socket */                do {                    printf("listen_sock=%d\n", listen_sock);                    conn_sock = accept(listen_sock,                                   (struct sockaddr *)&cli_addr, &clilen);                    if (conn_sock < 0)                        continue;                    setnonblocking(conn_sock);                    ev.events = EPOLLIN|EPOLLET;                    ev.data.fd = conn_sock;                    if (epoll_ctl(epollfd, EPOLL_CTL_ADD, conn_sock, &ev)                            == -1) {                        printf("epoll_ctl for conn_sock ERROR\n");                        exit(1);                    }                } while(conn_sock != -1);            } else { /* regular connection */                serve(events[n].data.fd);                ev.events = EPOLLIN|EPOLLET;                ev.data.fd = conn_sock;                if (epoll_ctl(epollfd, EPOLL_CTL_DEL, events[n].data.fd, &ev)                        == -1) {                    printf("epoll_ctl DEL ERROR\n");                    exit(1);                }                close(events[n].data.fd);            }        }    }    return 0;}

參考資料：

• 《UNIX環境進階編程》
• Using poll() instead of select()
• Man pages