如何修改这个迭代服务器以获得最高的文件描述符？

Question

在我的主函数中，我创建了（使用教程等）一个迭代服务器，它仅接收消息并将其返回给客户端。但是，我将 FD_SETSIZE 传递到 select() 函数，我认为这实际上并没有将文件描述符从最大值增加 1。

#include <dns_sd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>

#include <string.h>
#include <errno.h>
#include <time.h>
#include <math.h>

#include <sys/select.h>      /* <===== */


#ifdef _WIN32
#include <process.h>
typedef int pid_t;
#define getpid  _getpid
#define strcasecmp  _stricmp
#define snprintf _snprintf
#else
#include <sys/time.h>       // For struct timeval
#include <unistd.h>         // For getopt() and optind
#include <arpa/inet.h>      // For inet_addr()
#endif

#include <netdb.h>
#include <sys/select.h>
#include <fcntl.h>
#include <err.h>

#define BUFFER_SIZE 1024
#define MAX_CLIENTS 100      /* <===== */


 // ... lots of skipped code here


/**
 * Creates a connection with a socket. It handles
 * socket(), bind().
 *
 * @name create_socket
 * @param server_addr the server address
 *
 */

int create_socket(struct sockaddr_in* server) {

    /* Create the listener socket as TCP socket */

    int sock = socket(PF_INET, SOCK_STREAM, 0); //use protocol family, internet

    if (sock < 0) {
        perror("socket()");
        exit(EXIT_FAILURE);
    }


    bzero(&*server, sizeof(*server)); // causing segault
    //server->sin_family = PF_INET;
    server->sin_family = AF_INET;
    //server->sin_addr.s_addr = INADDR_ANY;
    server->sin_addr.s_addr = htonl(INADDR_ANY);

    unsigned short port = 8129;
    server->sin_port = htons(port); //the port is chosen as the first available.

    int len = sizeof(*server);

    if (bind(sock, (struct sockaddr*) &*server, len) < 0) {
        perror("bind()");
        exit(EXIT_FAILURE);
    }

    return sock;
}

主要功能如下：

/** MAIN **/

int main()
{

    /* Socket Structures */
    struct sockaddr_in server, client, temp;
    fd_set readfds;
    int client_sockets[ MAX_CLIENTS ]; /* client socket fd list */
    int client_socket_index = 0;  /* next free spot */


    /* Create the listener socket as TCP socket */
    int sock = create_socket(&server);

    listen(sock, 5); /* 5 is number of waiting clients */
    //printf("Listener bound to port %d\n", port);

    printf("Started server; listening on port: %d\n", local_port);

    /** Read from and Write to the Client **/

    int fromlen = sizeof( client );

    char buffer[ BUFFER_SIZE ];

    int i;

    while ( 1 )
    {
#if 1
        struct timeval timeout;
        timeout.tv_sec = 3;
        timeout.tv_usec = 500;  /* 3 AND 500 microseconds */
#endif

        FD_ZERO( &readfds );
        FD_SET( sock, &readfds ); // FD_SET to include listener fd, sock

        for ( i = 0 ; i < client_socket_index ; i++ )
        {
            FD_SET( client_sockets[ i ], &readfds ); //Set FD_SET to include client socket fd
        }

#if 0
        /* BLOCK */
        int ready = select( FD_SETSIZE, &readfds, NULL, NULL, NULL );
        /* ready is the number of ready file descriptors */
        printf( "select() identified %d descriptor(s) with activity\n", ready );
#endif

#if 1
        int ready = select( FD_SETSIZE, &readfds, NULL, NULL, &timeout );
        if ( ready == 0 ) {
        //printf( "No activity\n" );
            continue;
        }
#endif

        if ( FD_ISSET( sock, &readfds ) )
        {
            int newsock = accept( sock,
                    (struct sockaddr *)&client,
                    (socklen_t *)&fromlen );
            /* this accept() call we know will not block */
            printf( "Accepted client connection\n" );
            client_sockets[ client_socket_index++ ] = newsock;
        }

        for ( i = 0 ; i < client_socket_index ; i++ )
        {
            int fd = client_sockets[ i ];

            if ( FD_ISSET( fd, &readfds ) )
            {
                int n, guess, success;

                /** Recieve user input, check for errors **/
                n = recv( fd, buffer, BUFFER_SIZE - 1, 0 );

                if ( n < 0 )
                {
                    perror( "recv()" );
                }
                else if ( n == 0 )
                {
                    int k;
                    printf( "Client on fd %d closed connection\n", fd );
                    close( fd );
                    /* remove fd from client_sockets[] array: */
                    for ( k = 0 ; k < client_socket_index ; k++ )
                    {
                        if ( fd == client_sockets[ k ] )
                        {
                            /* found it -- copy remaining elements over fd */
                            int m;
                            for ( m = k ; m < client_socket_index - 1 ; m++ )
                            {
                                client_sockets[ m ] = client_sockets[ m + 1 ];
                            }
                            client_socket_index--;
                            break;  /* all done */
                        }
                    }

                } else {

                    buffer[n] = '\0';

                    printf("Recieved %s",buffer);

                    n = send(fd, buffer, strlen(buffer), 0);

                    /* Divide input into parts and get the guess */


                }
            }
        }
    }

    return EXIT_SUCCESS; /* we never get here */
}

Answer 1

又用谷歌搜索了几个小时，我终于明白了！变化很小。

while(1) {
//...
    int maxfd = sock;

    for ( i = 0; i < client_socket_index ; i++ )
    {
        int sd = client_sockets[i];
        FD_SET( sd, &readfds ); //Set FD_SET to include client socket fd
        if(sd > maxfd)
            maxfd = sd;
    }

    int ready = select(maxfd+1, &readfds, NULL, NULL, &timeout );

}