socket and fork with c

Question

Here a piece of my fork-server code:

    signal (SIGINT, ( void *)sig_handler);
while(1){
    memset(&cli_addr, 0, sizeof(cli_addr));

    if((newsockd = accept(sockd, (struct sockaddr *) &cli_addr, (socklen_t *) &socket_len)) < 0){
        perror("Errore nella connessione\n");
        onexit(newsockd, sockd, 0, 2);
    }
    fprintf(stdout, "Ricevuta richiesta di connessione dall' indirizzo %s\n", inet_ntoa(cli_addr.sin_addr));

    child_pid = fork();
    if(child_pid < 0){
        perror("Fork error");
        onexit(newsockd, sockd, 0, 2);
    }
    if(child_pid == 0){
        do_child(newsockd);
    }
    else{
        attended_pid = waitpid(child_pid, NULL, 0);
        if(attended_pid != child_pid){
            printf("Child error");
        }
    }
}

My question is: have i to close the main sock (sockd) before executing the client?
I think no but:

i've added a "sigint controller" and if i press CTRL-C on the server (with commented sockd -> //close(sockd);) the sigint will be executed 3 times with 2 concurrent connection (why??)
if i have this code close(sockd) the sigint will be executed only 1 time but i got an :bad file descriptor on the accept instruction.

So, what have i to do?
Thanks!

PS: my sigint code:

void sig_handler(const int signo, const int sockd, const int newsockd){
  if (signo == SIGINT){
    printf("Ricevuto SIGINT, esco...\n");
    if(newsockd) close(newsockd);
    if(sockd) close(sockd);
    exit(EXIT_SUCCESS);
  }
}

off topic: 0 is a valid socket/file descriptor. So you should better initialize an unused socket/file descriptor to -1 before usage and after having close()ed it and then use -1 to test if it's a valid one or not. — alk
In the parent process, you should call e.g. waitpid at regular intervals to clean up after your children. — Some programmer dude
thanks :) i've re-updated my code but...what have i to "clean up" into the parent?? — polslinux

Some programmer dude Some programmer dude · Accepted Answer · 2012-09-05T07:43:10

From the fork(2) manual page:

The child inherits copies of the parent's set of open file descriptors. Each file descriptor in the child refers to the same open file description (see open(2)) as the corresponding file descriptor in the parent. This means that the two descriptors share open file status flags, current file offset, and signal-driven I/O attributes (see the description of F_SETOWN and F_SETSIG in fcntl(2)).

This tells me that you should not close the listening socket in the child process. You shouldn't close the accepted socket in the parent process either, but let it be closed by the child process when it's done.

socket and fork with c

1 Answers