AAE-CNAS-Labs/Topic-2/task_2_4.c

//
// Wrote for Computer Networks and Systems lab classes
// AUTHOR : Sergiusz Warga

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

const char * time_from_main_exec() {
    struct timeval now;
    gettimeofday(&now, NULL);
    char buff[127];
    sprintf(&buff, "us : %d", now.tv_usec);
    return buff;
}

void parent_before_child() {
    pid_t pid;
    printf("\nparent_before_child()\n");
    pid = fork();
    if (pid == -1) {    // If something went wrong.
        perror("Fork: ");
        exit(EXIT_FAILURE);
    }
    if (pid != 0) {     // If this is a parent process.
        printf("===\n%s\nI am a parent.\nMy PID is: %d\n===", time_from_main_exec(), getpid());
        kill(getpid(), SIGTERM);
    } else {
        sleep(1);
        printf("===\n%s\nI am a child.\nMy PID is: %d\n===", time_from_main_exec(), getpid()); // This line will not be printed, as (usually) parent process will finish
        // its execution in less than 1 second
    }
}

void child_before_parent() {
    pid_t pid;
    printf("\nchild_before_parent()\n");
    printf("PID before fork: %d\n", getpid());
    pid = fork();
    if (pid == -1) {    // If something went wrong.
        perror("Fork: ");
        exit(EXIT_FAILURE);
    }
    if (pid == 0) {     // If this is a parent process.
        printf("===\n%s\nI am a child.\nMy PID is: %d\n===", time_from_main_exec(), getpid());
        kill(getpid(), SIGTERM);
    } else {
        sleep(1);
        printf("===\n%s\nI am a parent.\nMy PID is: %d\n===", time_from_main_exec(), getpid());
    }
}


int main() {
    
    pid_t pid;
    printf("%s: Grandparent process has PID: %d\n", time_from_main_exec(), getpid());
    pid = fork();
    if (pid == 0) { // If child process
        printf("%s: Process with PID %d will execute funs.\n", time_from_main_exec(), getpid());
        child_before_parent();
        sleep(1);
        parent_before_child();
        sleep(1);
    } else {        // If parent process
        printf("%s: Grandparent's child process has PID: %d\n", time_from_main_exec(), pid);
        sleep(5);
    }
    return 0;
}