Everytime ctrl + z is pressed a random number is generated

Question

Moving straight to the issue, how do I make Ctrl+z do what the title states?

My program implements a parent process which creates a single child process. Both processes will display the process ID and once the child terminates a signal is sent to the parent process and the parent signal handler will display a text stating a signal has been captured.

On the child process, on top of displaying the child's process ID, it must generate a random number between 10 and 50 every time Ctrl + z is pressed. So far I can only make the child process generate 1 random number.

Below is my code:

void main() {
    int pid;
    int x;
    int fd[2];
    const int MAXLINE=4096;
    char line[MAXLINE];

    pid=fork();

    if (pipe(fd) < 0) {
    printf("Pipe error!");
    } 


    if (pid < 0) {
        printf("Fork error!");
    } else if (pid == 0) {                          //Child process
        signal(SIGTSTP, childsignal_handler);
        printf("The process id is: %i\n", getpid());
        sleep(1000);                            //Implemented to wait for a signal
    } else {
        printf("The process id is: %i\n", getpid());            //Parent process
        pause();                            //Waits for the Child process to finish
    }

}

parent signal handler:

void parentsignal_handler(int signo) {                      //Signal Handler for the parent process
    printf("The signal in the parent process has been captured\n");
}

child signal handler:

void childsignal_handler(int signo) {                       //Signal Handler for the child process
    signal(SIGTSTP, childsignal_handler);
    printf("\nThe signal in the child process has been captured\n");
    randomnumbergenerator();
    pause();
}

The random number generator:

void randomnumbergenerator() {                          //Random number generator to run everytime Ctrl+z is pressed
    //signal(SIGTSTP, childsignal_handler);
    int number;
    int number2 = 10;
    printf("Welcome to random number generator!");
    printf("\nRandom number generated = %d\n", rand() % 40 + 10);
}

PS: I have read several documentations regarding various solutions such as sigsuspend, sigprocmask,pause and so on but none of them worked so far.

below are some of the documentations i have read so far:

https://www.gnu.org/software/libc/manual/html_node/Waiting-for-a-Signal.html#Waiting-for-a-Signal https://man7.org/linux/man-pages/man2/pause.2.html

Calling `pause()` in the signal handler seems like a really bad idea. (Also, `printf` should be avoided in signal handlers because it is not an "async-safe" function.) — Ian Abbott, Mar 24 '21 at 16:27
the next for the program was to redirect printf to a file using dup2 and i havent implemented them yet — Jimmy, Mar 24 '21 at 17:44
In _the parent signal handler will display a text stating a signal has been captured_, do you mean by _will_ that this is supposed to happen in a hypothetical future version of your program? — Armali, Mar 24 '21 at 18:11
@Armali yes sir i need to implement a signal that will detect the child terminating — Jimmy, Mar 24 '21 at 18:17
Is this a [homework problem that others are also working on](https://stackoverflow.com/q/66773153/132382)? — pilcrow, Mar 24 '21 at 23:17

score 0 · Accepted Answer · answered Mar 24 '21 at 19:08

i need to implement a signal that will detect the child terminating

You don't exactly need to implement a signal; you just need to install the handler that you already have:

    signal(SIGCLD, parentsignal_handler);

how do I make Ctrl+z do what the title states?
So far I can only make the child process generate 1 random number.

To prevent the parent process from being suspended (and therewith losing signal delivery), ignore the STOP signal in the parent:

    signal(SIGTSTP, SIG_IGN);

And you should really pay attention to Ian Abbott's first comment and remove pause() from the signal handler; otherwise after Ctrl-Z was pressed the program will not end. At the same time change sleep(…) to while (sleep(…)) to keep a timed suspension instead of the unlimited pause().

thank you and yes i have already made amendments to the program — Jimmy, Mar 24 '21 at 20:19

Everytime ctrl + z is pressed a random number is generated

1 Answers1