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

volatile sig_atomic_t should_exit;
volatile sig_atomic_t is_blocked;
volatile sig_atomic_t is_pending;
void alarm_went_off(int sig, siginfo_t *info, void *_context);

void fast_block(void) {
    is_blocked++;
}
void fast_unblock(void) {
    if ((--is_blocked == 0) && is_pending)
        alarm_went_off(SIGALRM, NULL, NULL);
}

void 
alarm_went_off(int sig, siginfo_t *info, void *_context)
{
    if (is_blocked) {
        is_pending = 1;
        return;
    }
    is_pending = 0;

    printf("Alarm went off\n");
    should_exit = 1;
}

int
main()
{
    signal_set_handler(SIGALRM, alarm_went_off);
    alarm(3);

    printf("main program running...\n");
    while (!should_exit) {
        for (int i = 0; i < 300000000; i++) {
            volatile int sqi = i * i;
        }

        fast_block();
        printf("main program here...\n");
        fast_unblock();
    }
    printf("main program done...\n");
}