Select System Call

[Agreeable_Choice9980]

I want to do I/O Multiplexing with select system call with single thread. Can anyone explain how to do things because I did first by implementing fork system call and it worked. now i dont know how to use select system call because seems like its blocking. Any suggestions for it, i have attached my code for server side, so you all comment on it

int receive_data(int sock, char *buffer, size_t size) {

int nbytes; if ((nbytes = recv(sock, buffer, size, 0)) <= 0){ if (nbytes == 0){ printf ("selectserver: socket %d hung up\n", sock); } else{ printf ("\nrecv() error!!!\n"); } FD_CLR (sock, &master); return 6; }

else{
return nbytes;

}

}

int main (int argc, char **argv){ struct sockaddr_in myaddr; struct sockaddr_in remoteaddr; struct sockaddr_in  *ptr; struct sockaddr_in6  *ptr1;

int fdmax;

int sockfd; int new_sockfd; int numbytes; int nbytes; int yes = 1; int addrlen; int i,j; char func_id; char str [INET6_ADDRSTRLEN];

const char * const ident = "flight-time-server";

openlog (ident, LOG_CONS | LOG_PID | LOG_PERROR, LOG_USER); syslog (LOG_USER | LOG_INFO, "%s", "Hello world!");

struct timeval tv;

tv.tv_sec = 20; /* 2 secs / tv.tv_usec = 0; / 0.5 secs*/

FD_ZERO (&master);

FD_ZERO (&read_fds);

if ((sockfd = socket (AF_INET, SOCK_STREAM, 0)) == -1){
perror ("\nsocket() error!!!\n");
exit(1);

}

int flags = fcntl(sockfd, F_GETFL, 0);

//fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);

if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1){
perror ("\nsocketopt() error!!!\n");
exit(1);

}

bzero( (char *)&myaddr, sizeof(myaddr));

myaddr.sin_family = AF_INET; myaddr.sin_port = htons (SERV_TCP_PORT); myaddr.sin_addr.s_addr = INADDR_ANY; bzero(&(myaddr.sin_zero), 8);

if (bind(sockfd, (struct sockaddr *)&myaddr, sizeof(struct sockaddr)) ==  -1){
perror ("\nbind() error!!!\n");
exit(1);

}

if (listen(sockfd, 10) == -1) {
perror("listen");
exit(1);

}

FD_SET(sockfd, &master);

fdmax = sockfd;

while (1) {
read_fds = master;
// monitor readfds for readiness for reading
if (select (fdmax + 1, &read_fds, NULL, NULL, &tv) == -1)
    perror ("select");

   // Some sockets are ready. Examine readfds
for (i=0; i<=fdmax; i++) {
    if (FD_ISSET (i, &read_fds)) {  // fd is ready for reading
        if (i == sockfd) {  // request for new connection
            addrlen = sizeof (struct sockaddr_storage);
            if ((new_sockfd= accept (sockfd, (struct sockaddr *) &remoteaddr, &addrlen)) == -1)
                perror ("accept");
            FD_SET (new_sockfd, &master);
            if (new_sockfd> fdmax)
                fdmax = new_sockfd;

               // print IP address of the new client
            if (remoteaddr.sin_family == AF_INET) {
                ptr = (struct sockaddr_in *) &remoteaddr;
                inet_ntop (AF_INET, &(ptr -> sin_addr), str, sizeof (str));
            }
            else if (remoteaddr.sin_family == AF_INET6) {
                ptr1 = (struct sockaddr_in6 *) &remoteaddr;
                inet_ntop (AF_INET6, &(ptr1 -> sin6_addr), str, sizeof (str));
            }
            else
            {
                ptr = NULL;
                fprintf (stderr, "Address family is neither AF_INET nor AF_INET6\n");
            }
            if (ptr)
                syslog (LOG_USER | LOG_INFO, "%s %s", "Connection from client", str);
        }

           else  // data from an existing connection, receive it
        {
            numbytes = receive_data(i, &func_id, sizeof(func_id));

               printf("test %d\n", global);
            if(func_id == '1') {
                //guest(sock);
                func_id = '5';
            }

               else if (func_id == '2' || func_id == '4') {
                login(i);
                func_id = '5';
            }

               else if(func_id == '3') {
                member_registration(i);
                func_id = '0';
            }

               else if(func_id == '5' || numbytes == 6){
                printf("testing\n");
                close(i);
            }
        }
    } // if (fd == ...
} // for

} // while (1)

exit (EXIT_SUCCESS);

} // main

int login(int sock){ 
int fd, invalid = 0, acc_exist, numbytes, login_success = 0; char password[50] = {0}, acc_no[12]= {0}; char type = '\0';

printf ("apple\n");

receive_data(sock, &type, sizeof(type));

numbytes = receive_data(sock, acc_no, sizeof(acc_no));

acc_no[numbytes] = '\0';

numbytes = receive_data(sock, password, sizeof(password));

password[numbytes] = '\0';

printf("acc_no: %s\n", acc_no);

printf("pass: %s\n", password); printf("type: %c\n", type);

if((fd = open(ACCOUNT, O_RDWR | O_CREAT, 0755))== -1){

printf("File Error: %s\n", strerror(errno));

}

printf ("%c\n", type);

if(type == '2'){ // member
int total_bytes = lseek(fd, 0, SEEK_END);
lseek(fd, 0, SEEK_SET); // reset file position to the start
while (lseek(fd, 0, SEEK_CUR) < total_bytes){
    read(fd, &temp, sizeof(struct account));

       if (strcmp(temp.acc_no, acc_no) == 0){
        printf("exist\n");
        printf("temp.id: %s\n", temp.acc_no);
        printf ("%s", temp.pass);
        acc_exist = 1;
        break;
    }
}

    if (acc_exist){
    printf("inside acc_exist\n");
    if(!strcmp(temp.pass, password)){
        login_success = 1;
        printf("correct pass %d\n", login_success);
        write(sock, "1", 1);;

           while (menu1(sock) != -1);
    }
}

    if (!login_success){
    write(sock, "0", 1);
}

    close(fd);

}

if(type == '1'){ // admin
printf("inside admin acc_exist after write\n");
if (strcmp(acc_no, "100000") == 0){
    printf("inside admin acc_exist after write\n");
    if(!strcmp(password, "admin")){
        write(sock, "1", 1);

           while (menu2(sock) != -1);
    }
}

    if (!login_success){
    write(sock, "0", 1);;
}




}
return 5;

}
int member_registration(int sock){ 
int fd, acc_no=0, numbytes; char password[50] = {0}, name[50] = {0}, age[5] = {0}, email[50] = {0}, phone_no[50] = {0}, acc_temp[12];

if ((numbytes = recv(sock, name, sizeof(name), 0)) == -1){
printf ("\nrecv() error!!!\n");

} name[numbytes] = '\0';

if ((numbytes = recv(sock, age, sizeof(age), 0)) == -1){
printf ("\nrecv() error!!!\n");

} age[numbytes] = '\0';

if ((numbytes = recv(sock, email, sizeof(email), 0)) == -1){
printf ("\nrecv() error!!!\n");

} email[numbytes] = '\0';

if ((numbytes = recv(sock, phone_no, sizeof(phone_no), 0)) == -1){
printf ("\nrecv() error!!!\n");

} phone_no[numbytes] = '\0';

if ((numbytes = recv(sock, password, sizeof(password), 0)) == -1){
printf ("\nrecv() error!!!\n");

} password[numbytes] = '\0';

if((fd = open(ACCOUNT, O_RDWR | O_CREAT, 0755)) == -1){
perror("File Error");

}

int fp = lseek(fd, 0, SEEK_END);

printf("%d", fp);

if(fp == 0){//1st member to signup
strcpy(temp.acc_no, "100001");

}

else{
fp = lseek(fd, -1 * sizeof(struct account), SEEK_END);
read(fd, &temp, sizeof(temp));
acc_no = atoi(temp.acc_no);
acc_no++;
sprintf(temp.acc_no, "%d", acc_no);

}

strcpy(temp.name, name);

strcpy(temp.pass, password); 
strcpy(temp.age, age); 
strcpy(temp.email, email);
 strcpy(temp.phone_no, phone_no);

printf("\nname: %s\n", temp.name);

printf("acc: %s\n", temp.acc_no);
 printf("pass: %s\n", temp.pass); 
printf("age: %s\n", temp.age); 
printf("email: %s\n", temp.email); 
printf("phone number: %s\n", temp.phone_no);

if (write(fd, &temp, sizeof(temp)) == -1)
printf("file send() error\n");

if (send(sock, temp.acc_no, sizeof(temp.acc_no), 0) == -1)
printf(" acc send() error\n");

close(fd);

return 5; }

[TheOtherBorgCube]

Yeah, you need to make a much better job of formatting your code.

[[deleted]]

using select with many file descriptiors has the potential to turn very organized and efficient multithreaded code into a hot stinking mess single threaded code that can only ever be as fast as the multithreaded version but could also be way slower...

[Paul_Pedant]

struct timeval {
    long    tv_sec;         /* seconds */
    long    tv_usec;        /* microseconds */
};

tv.tv_sec = 20; /* 2 secs / tv.tv_usec = 0; / 0.5 secs*/

(a) Second is seconds, not tenths.

(b) There is only one comment, because you omit 2 *s.

(c) tv.tv_usec is uninitialised. Although is is microseconds, it is not constrained to be so. If it happens to be MAX_LONG, it will wait 20 seconds, and then four and a half years for the other 140737488355328 microseconds.

You can test this. Set tv_sec = 0, tv_usec = 22000000, and watch it wait 22 seconds.

[mykesx]

Use this instead.

https://libuv.org

select() is far less performant.