Question

我正在为我正在制作的聊天客户端编写服务器问题如下如果网络客户端连接，则仅选择提升其块如果最后连接的客户端正在写。例：我连接了4个客户端服务器将一直阻塞，直到客户端没有。 4写道如果客户端1-3写入它保持阻止我究竟做错了什么？在这里分析我的代码可能包含丑陋和无用的代码但那只是分析它的行为

Server.c ++

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h> 
#include <sys/socket.h>
#include <netinet/in.h>
#include <boost/thread/thread.hpp>
#include <sys/time.h>
#include <sys/ioctl.h>

using namespace std;

void error(char *msg, int socket) {
    perror(msg);
    close(socket);
    exit(1);
}

int main(int argc, char** argv) {
    int sockfd, newsockfd, portno, n, highsock;
    socklen_t clilen;
    fd_set readfds;
    list<int> CliSocks;
    FD_ZERO(&readfds);
    /*
     * Sockfd, newsockfd contain values returned by the socket
     * portno stores the port number on which the server accepts connections
     * clilen stores the size of the address of the client
     * n contains the amount of character written of read
     */
    char buffer[256];
    /* buffer contains the characters read from the socket*/

    struct sockaddr_in serv_addr, cli_addr;
    /* 
     * sockaddr_in contains an internet address
     * serv_addr contains the servers address
     * cli addr contains the clients address
     */
    if (argc < 2) {
        fprintf(stderr, "ERROR no port provided");
        exit(1);
    }
    /*
     * error if no argument
     */
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    highsock = sockfd;
    FD_SET(sockfd, &readfds);
    int opt = 1;
    ioctl(sockfd, FIONBIO, &opt);

    if (sockfd < 0) {
        error("ERROR opening socket", sockfd);
    }
    /*
     * socket() creates a new socket
     * argument 1 contains the address domain
     * argument 2 contains the socket type
     * argument 3 contains the protocol should be 0
     * socket() returns a reference for itself
     */
    bzero((char*) &serv_addr, sizeof (serv_addr));
    /* empty the serv_addr variable*/
    portno = atoi(argv[1]);
    /*converts the port argument from string  to int*/
    serv_addr.sin_family = AF_INET;
    /*set the code for the address family*/
    serv_addr.sin_port = htons(portno);
    /*htons converts the portno to network bytes and gives it to the server address*/
    serv_addr.sin_addr.s_addr = INADDR_ANY;
    /*set the server ip to the ip of the running machine*/
    if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof (serv_addr)) < 0)
        error("ERROR on binding", sockfd);
    /*
     * bind() binds a socket to an address, in this case the
     * addess of the current host
     */
    listen(sockfd, 5);

    /*the listen system call allows the process to listen on the socket for connections*/


    while (1) {
        int sockcount = select(highsock + 1, &readfds, NULL, NULL, NULL);

        clilen = sizeof (cli_addr);
        newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);
        /*
         * accept() lets the system wait until a client connects to the server
         */

        if (newsockfd > 0) {
            ioctl(newsockfd, FIONBIO, &opt);
            FD_SET(newsockfd, &readfds);
            highsock = newsockfd;
            CliSocks.push_back(newsockfd);
        }


        for (list<int>::iterator it = CliSocks.begin(); it != CliSocks.end(); it++) {
            bzero(buffer, 256);
            n = read(*it, buffer, 255);
            if(buffer[0] != 0){
            printf("Here is the message: %s", buffer);

            /*
             * bzero empties the buffer
             * read obviously reads data from the new socket descriptor
             */
            n = write(*it, "I got your message", 18);
            if (n < 0) error("ERROR writing to socket", sockfd);
                        }
        }
    }
    close(sockfd);
    return 0;
}

Answer 1

问题是，在调用readfds之前，您必须每次都在循环中重置select。这是因为对select 的调用会修改其参数。

while (1) {
    FD_ZERO(&readfds);
    FD_SET(sockfd, &readfds);
    highsock = sockfd;
    for (list<int>::iterator it = CliSocks.begin(); it != CliSocks.end(); it++) {
        FD_SET(*it, &readfds);
        highsock = *it > highsock ? *it : highsock;
    }
    int sockcount = select(highsock + 1, &readfds, NULL, NULL, NULL);

    ...
}

c ++ select仅检查最后一个客户端套接字

1 个答案: