// Program 8.1

#include <math.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
 
int main(int argc,  char *argv[]) {
   int i;
   sigset_t intmask;
   int repeatfactor;
   double y = 0.0;
 
   if (argc != 2) {
      fprintf(stderr, "Usage: %s repeatfactor\n", argv[0]);
      return 1; 
   }   
   repeatfactor = atoi(argv[1]);
   if ((sigemptyset(&intmask) == -1) || (sigaddset(&intmask, SIGINT) == -1)){
      perror("Failed to initialize the signal mask");
      return 1;
   }
   for ( ; ; ) {
      if (sigprocmask(SIG_BLOCK, &intmask, NULL) == -1)
         break; 
      fprintf(stderr, "SIGINT signal blocked\n");
      for (i = 0; i < repeatfactor; i++) 
         y += sin((double)i);
      fprintf(stderr, "Blocked calculation is finished, y = %f\n", y);
      sleep(3);
      if (sigprocmask(SIG_UNBLOCK, &intmask, NULL) == -1)
         break;
      fprintf(stderr, "SIGINT signal unblocked\n");
      for (i = 0; i < repeatfactor; i++) 
         y += sin((double)i);
      fprintf(stderr, "Unblocked calculation is finished, y=%f\n", y);
      sleep(3);
   }    
   perror("Failed to change signal mask");
   return 1;
}