1b.c

/*
============================================================================
Name : 1b
Author : Piyush Singh
Description :  Write a separate program (for each time domain) to set a interval timer in 10sec and
10micro second
a. ITIMER_REAL
b. ITIMER_VIRTUAL
c. ITIMER_PROF
Date: 18th Sep, 2025.
============================================================================
*/


#include <stdio.h>      // For printf(), perror()
#include <stdlib.h>     // For exit()
#include <sys/time.h>   // For setitimer(), struct itimerval
#include <unistd.h>     // For pause(), getppid()
#include <signal.h>     // For signal(), SIGVTALRM

// Signal handler for SIGVTALRM
void virtual_handler(int signum) 
{ printf("🎯 ITIMER_VIRTUAL triggered: SIGVTALRM received\n"); }

int main() 
{
    // Register signal handler for SIGVTALRM
    signal(SIGVTALRM, virtual_handler);

    // Define timer structure
    struct itimerval timer;

    // Set initial expiration to 10 seconds and 10 microseconds
    timer.it_value.tv_sec = 10;
    timer.it_value.tv_usec = 10;

    // Set interval to 0 (one-shot timer)
    timer.it_interval.tv_sec = 0;
    timer.it_interval.tv_usec = 0;

    // Start the virtual timer
    if (setitimer(ITIMER_VIRTUAL, &timer, NULL) == -1) 
    {
        perror("❌ setitimer failed");
        exit(1);
    }

    printf("🟢 ITIMER_VIRTUAL set for 10s + 10μs\n");

    // Consume user CPU time to trigger the timer
    // Use a volatile variable to prevent compiler optimization
    volatile long sink = 0;
    for (long i = 0; i < 1e9; i++) 
        sink += i;  // Keeps CPU busy

    // Optional: sleep to allow signal to print before exit
    sleep(1);

    return 0;
}

/*
============================================================================
Output :

============================================================================
*/