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 (int argc, char **argv)
  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     long divisor;
  53
  54     if (argc > 1) {
  55         char *endptr;
  56
  57         errno = 0;
  58         divisor = strtol (argv[1], &endptr, 0);
  59         if ((endptr && *endptr)
  60             || (errno == ERANGE && (divisor == LONG_MAX || divisor == LONG_MIN))
  61             || (errno && divisor == 0)) {
  62             err (EXIT_FAILURE, "Can't read `%s' as integer", argv[1]);
  63         }
  64     }
  65     else {
  66         divisor = 250;
  67     }
  68
  69     act.sa_handler = sighandler;
  70     if (sigemptyset (&act.sa_mask)) {
  71         err (EXIT_FAILURE, "sigemptyset failed");
  72     }
  73     act.sa_flags = 0;
  74
  75     it.it_interval.tv_sec = 0;
  76     it.it_interval.tv_usec = 1000000 / divisor;
  77     it.it_value.tv_sec = 0;
  78     it.it_value.tv_usec = 1000000 / divisor;
  79
  80     if (sigaction (SIGALRM, &act, NULL)) {
  81         err (EXIT_FAILURE, "sigaction failed");
  82     }
  83
  84     if (setitimer (ITIMER_REAL, &it, NULL)) {
  85         err (EXIT_FAILURE, "setitimer failed");
  86     }
  87
  88     hog (ULONG_MAX);
  89     for (i = 0; i < HIST; ++i) {
  90         v[i] = ULONG_MAX - hog (ULONG_MAX);
  91     }
  92
  93     for (i = 0; i < HIST; ++i) {
  94         printf ("%d = %ld\n", i, v[i]);
  95         tmp += v[i];
  96     }
  97     tmp /= HIST;
  98     n = tmp - (tmp / 3);
  99
 100     if (sigemptyset (&set)) {
 101         err (EXIT_FAILURE, "sigemptyset failed");
 102     }
 103
 104     if (sigaddset (&set, SIGALRM)) {
 105         err (EXIT_FAILURE, "sigaddset failed");
 106     }
 107
 108     for (;;) {
 109         int signr;
 110
 111         hog (n);
 112         if (sigwait (&set, &signr)) {
 113             err (EXIT_FAILURE, "sigwait failed");
 114         }
 115     }
 116 }