CODEWITHSUNDEEP
c
Nayan
Nayan

Reputation: 163

How to restart a child process from parent process in c

How to restart the child process from parent process when child process terminates. In one application I have created a child process which has an infinite while loop. The application runs in a router. When some event happens my child process terminates. But after rebooting the router everything works fine. Is it possible to restart my child process from parent process(parent process always works).

int main()
{
    pid_t pid;
    pid = fork();
    if (pid == 0)
    {
        while(1)
        {
            printf("Child process\n");
            sleep(1);
        }
    }
    else
    {
        while(1)
        {
            printf("parrent process\n");
        }
    }

    return 0;
}

Upvotes: 2

Views: 989

Answers (1)

Joshua
Joshua

Reputation: 43317

Assuming you only start one process and it's another executable:

pid_t pid = 0;
void sigchld(int unused)
{
    if (pid) {
        int status = 0;
        waitpid(pid, &status, WNOHANG);
        if (WIFSTOPPED(status) || WIFCONTINUED(status)) return;
        if (!WIFSIGNALED(status)) return; // It exited rather than terminated
        pid = 0;
    }
    if ((pid = vfork() == 0) {
        /* fork() isn't really signal safe anymore but vfork() still is! */
        execle(...);
        _exit(0);
    }
}

int main()
{
    pid = 0;
    struct sigaction sa;
    memset(&sa, 0, sizeof(sa));
    sa.sa_handler = sigchld;
    sa.sa_flags = SA_NODEFER;
    sigaction(SIGCHLD, &sa, NULL);
    kill(SIGCHLD, getpid());
    while(1)
    {
        printf("parrent process\n");
    }
}

Trivially adaptable to more than one, but if it's not another executable you have your work cut out from you. Attempting to fork() and run more code inside the signal handler is fraught with pearl. fork() itself is only safe if you haven't installed any pthread_atfork() handlers (which don't run in vfork()). You cannot call malloc() in a signal handler, and stdio is unreasonably tricky and best to assume it just doesn't work.

Upvotes: 1

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