#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <signal.h>

int sum;

int calculate(int first, int second) {
    sum = first + second;
    sleep(3); // represent I/O intensive function call
    return sum;
}


void signal_handler(int signal_number) {
    sum = 50 + 60;
    printf("Interrupt caught!\n");
    printf("Result from signal_handler: %d\n", sum);
    printf("---\n");
}

int main()
{
    
    sigset_t prevMask, blockMask;
    sigemptyset(&blockMask);
    sigaddset(&blockMask, SIGINT);

    struct sigaction sa;
    sa.sa_handler = signal_handler;
    sa.sa_flags = SA_RESTART;

    if(sigaction(SIGINT, &sa, NULL) == -1) {
        perror("sigaction");
        exit(EXIT_FAILURE);
    }

    for (;;) {
        if (sigprocmask(SIG_BLOCK, &blockMask, &prevMask) == -1) {
            perror("sigprocmask");
        }

        printf("Result from main: %d\n", calculate(3, 5));
        printf("---\n");

        if(sigprocmask(SIG_SETMASK, &prevMask, NULL) == -1) {
            perror("sigprocmask");
        }
    }
    return 0;
}