hog.c

   1 /* cc -o hog hog.c */
   2 #define _POSIX_PTHREAD_SEMANTICS
   3 #include <time.h>
   4 #include <stdio.h>
   5 #include <errno.h>
   6 #include <stdarg.h>
   7 #include <string.h>
   8 #include <limits.h>
   9 #include <stdlib.h>
  10 #include <signal.h>
  11 #include <sys/time.h>
  12
  13 #define HIST 10
  14
  15 static volatile sig_atomic_t stop;
  16
  17 static void sighandler (int signr)
  18 {
  19     (void) signr;
  20     stop = 1;
  21 }
  22
  23 static unsigned long hog (unsigned long niters)
  24 {
  25     stop = 0;
  26     while (!stop && --niters)
  27         ;
  28     return niters;
  29 }
  30
  31 static void err (int status, const char *fmt, ...)
  32 {
  33     va_list ap;
  34     int errno_code = errno;
  35
  36     va_start (ap, fmt);
  37     vfprintf (stderr, fmt, ap);
  38     va_end (ap);
  39     fprintf (stderr, ": %s\n", strerror (errno_code));
  40     exit (status);
  41 }
  42
  43 int main (void)
  44 {
  45     unsigned int i;
  46     struct itimerval it;
  47     struct sigaction act;
  48     sigset_t set;
  49     unsigned long v[HIST];
  50     double tmp = 0.0;
  51     unsigned long n;
  52
  53     act.sa_handler = sighandler;
  54     if (sigemptyset (&act.sa_mask)) {
  55         err (EXIT_FAILURE, "sigemptyset failed");
  56     }
  57     act.sa_flags = 0;
  58
  59     it.it_interval.tv_sec = 0;
  60     it.it_interval.tv_usec = 1000000 / 1000;
  61     it.it_value.tv_sec = 0;
  62     it.it_value.tv_usec = 1000000 / 1000;
  63
  64     if (sigaction (SIGALRM, &act, NULL)) {
  65         err (EXIT_FAILURE, "sigaction failed");
  66     }
  67
  68     if (setitimer (ITIMER_REAL, &it, NULL)) {
  69         err (EXIT_FAILURE, "setitimer failed");
  70     }
  71
  72     hog (ULONG_MAX);
  73     for (i = 0; i < HIST; ++i) {
  74         v[i] = ULONG_MAX - hog (ULONG_MAX);
  75     }
  76
  77     for (i = 0; i < HIST; ++i) {
  78         printf ("%d = %ld\n", i, v[i]);
  79         tmp += v[i];
  80     }
  81     tmp /= HIST;
  82     n = tmp - (tmp / 3);
  83
  84     if (sigemptyset (&set)) {
  85         err (EXIT_FAILURE, "sigemptyset failed");
  86     }
  87
  88     if (sigaddset (&set, SIGALRM)) {
  89         err (EXIT_FAILURE, "sigaddset failed");
  90     }
  91
  92     for (;;) {
  93         int signr;
  94
  95         hog (n);
  96         if (sigwait (&set, &signr)) {
  97             err (EXIT_FAILURE, "sigwait failed");
  98         }
  99     }
 100 }