task3.c

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

void signalHandler(int sig) {
    switch (sig) {
    SIGUSR1:
        printf("Hello from child!\n");
        break;
    SIGUSR2:
        break;

        default:
            break;
    }
}

int main(void) {
    pid_t pid = fork();

    if (pid == 0) {
        // Child process
        printf("[Child] pid %d \n", getpid());

        signal(SIGUSR1, NULL);
        sleep(13);

        signal(SIGUSR1, signalHandler);

        signal(SIGUSR2, signalHandler);
        sleep(3);

        _exit(EXIT_SUCCESS);
    } else if (pid > 0) {
        // Parent process
        sleep(5);
        kill(pid, SIGUSR2);
        alarm(13);

        while (1) {
            // Break if child terminated
            if (wait(NULL)) break;

            sleep(5);
            kill(pid, SIGUSR1);
        }
    }

    return EXIT_SUCCESS;
}