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How will a parent process know that a child is dead?

+1 vote
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How will a parent process know that a child is dead?
posted Nov 30, 2015 by Kali Mishra

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1 Answer

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Fork returns the child pid (process identifier) in the parent process, using the waitpid parent can not if child is alive or not

Something like

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


int  main(int argc, char *argv[])
{
    pid_t cpid, w;
    int status;


    cpid = fork();
    if (cpid == -1) { perror("fork"); exit(EXIT_FAILURE); }


    if (cpid == 0) {            /* Code executed by child */
        printf("Child PID is %ld\n", (long) getpid());
        if (argc == 1)
            pause();                    /* Wait for signals */
        _exit(atoi(argv[1]));
    } else {                    /* Code executed by parent */
        do {
            w = waitpid(cpid, &status, WUNTRACED | WCONTINUED);
            if (w == -1) { perror("waitpid"); exit(EXIT_FAILURE); }


            if (WIFEXITED(status)) {
                printf("exited, status=%d\n", WEXITSTATUS(status));
            } else if (WIFSIGNALED(status)) {
                printf("killed by signal %d\n", WTERMSIG(status));
            } else if (WIFSTOPPED(status)) {
                printf("stopped by signal %d\n", WSTOPSIG(status));
            } else if (WIFCONTINUED(status)) {
                printf("continued\n");
            }
        } while (!WIFEXITED(status) && !WIFSIGNALED(status));
        exit(EXIT_SUCCESS);
    }
}

Output

$ ./a.out &
Child PID is 12345
[1] 12344
$ kill -STOP 12345
stopped by signal 19
$ kill -CONT 12345
continued
$ kill -TERM 12345
killed by signal 15
[1]+  Done                    ./a.out
answer Dec 1, 2015 by Salil Agrawal
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