CODEWITHSUNDEEP
cpipesignalsfork
Ryan
Ryan

Reputation: 73

Trouble Killing Parent Process after Fork, C

I'm trying to refresh some C skills, and I'm playing with code to fork and communicate between the two processes.

In the program below, I expected that the child's SIGINT signal would cause the parent to terminate before it printed that the child has died. However, the message "Parent: chlid is dead" is still the last thing to be printed.

Is there something I'm missing?

Thanks.

#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <signal.h>

int main() {
    char *msg;
    int forkval, parentpid;
    int p2c[2];

    pipe(p2c);

    forkval = fork();

    if (forkval < 0) exit(EXIT_FAILURE);

    if (forkval) { /* Parent */
        msg = "Parent: reporting\n";
        close(p2c[0]);
        write(STDOUT_FILENO,msg,strlen(msg));
        write(p2c[1], &forkval, sizeof(int));
        close(p2c[1]);
        wait(NULL);
        msg = "Parent: chlid is dead\n";
        write(STDOUT_FILENO, msg, strlen(msg));
    } else { /* Child */
        msg = "Child: reporting\n";
        close(p2c[1]);
        write(STDOUT_FILENO,msg,strlen(msg));
        read(p2c[0], &parentpid, sizeof(int));
        close(p2c[0]);
        fprintf(stdout, "Child: parent's pid is %i\n", parentpid);
        kill(parentpid,SIGINT);
        fprintf(stdout, "Child: dying\n");
    }
    exit(EXIT_SUCCESS);
}

Terminal output:

Parent: reporting
Child: reporting
Child: parent's pid is 10940
Parent: chlid is dead

Upvotes: 2

Views: 549

Answers (1)

user3386109
user3386109

Reputation: 34829

The nonzero value that fork returns is the pid of the child. So the child is killing itself, and that's why you don't see the "Child: dying" message from the child, but do see the last message from the parent.

Upvotes: 1

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