hog.c

   1 /* gcc -o hog hog.c */
   2 #define _GNU_SOURCE
   3 #include <err.h>
   4 #include <time.h>
   5 #include <stdio.h>
   6 #include <sched.h>
   7 #include <limits.h>
   8 #include <stdlib.h>
   9 #include <signal.h>
  10 #include <sys/time.h>
  11
  12 #define HIST 10
  13
  14 static volatile sig_atomic_t stop;
  15
  16 static void sighandler (int signr)
  17 {
  18     (void) signr;
  19     stop = 1;
  20 }
  21
  22 static unsigned long hog (unsigned long niters)
  23 {
  24     stop = 0;
  25     while (!stop && --niters)
  26         ;
  27     return niters;
  28 }
  29
  30 int main (void)
  31 {
  32     unsigned int i;
  33     struct itimerval it;
  34     sigset_t set;
  35     unsigned long v[HIST];
  36     double tmp = 0.0;
  37     unsigned long n;
  38
  39     it.it_interval.tv_sec = 0;
  40     it.it_interval.tv_usec = 1;
  41     it.it_value.tv_sec = 0;
  42     it.it_value.tv_usec = 1;
  43
  44     if (signal (SIGALRM, &sighandler)) {
  45         err (EXIT_FAILURE, "failed to set signal handler");
  46     }
  47
  48     if (setitimer (ITIMER_REAL, &it, NULL)) {
  49         err (EXIT_FAILURE, "failed to set interval timer");
  50     }
  51
  52     hog (ULONG_MAX);
  53     for (i = 0; i < HIST; ++i) {
  54         v[i] = ULONG_MAX - hog (ULONG_MAX);
  55     }
  56
  57     for (i = 0; i < HIST; ++i) {
  58         printf ("%d = %ld\n", i, v[i]);
  59         tmp += v[i];
  60     }
  61     tmp /= HIST;
  62     n = tmp - (tmp / 3);
  63
  64     if (sigemptyset (&set)) {
  65         err (EXIT_FAILURE, "failed to empty sigset");
  66     }
  67
  68     if (sigaddset (&set, SIGALRM)) {
  69         err (EXIT_FAILURE, "failed to add to sigset");
  70     }
  71
  72     for (;;) {
  73         int signr;
  74
  75         hog (n);
  76         if (sigwait (&set, &signr)) {
  77             err (EXIT_FAILURE, "failed to wait for a signal");
  78         }
  79     }
  80
  81     return 0;
  82 }