Program that triggers N wakeups per second

wake.cpp

#include <mach/mach_init.h>
#include <mach/task.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>
#include <unistd.h>

static void
Error(const char *aMsg)
{
  fprintf(stderr, "error: %s\n", aMsg);
  exit(1);
}

static bool
GetTaskPowerInfo(struct task_power_info* aInfo)
{
  mach_msg_type_number_t count = TASK_POWER_INFO_COUNT;
  kern_return_t kr =
    task_info(mach_task_self(), TASK_POWER_INFO, (task_info_t)aInfo, &count);
  return kr == KERN_SUCCESS;
}

// Set in main() from the command line.
static long gFreq = 0;

static void
SigprofHandler(int aSigNum, siginfo_t* aInfo, void *aContext)
{
  static int n = 0;
  if (n++ % gFreq == 0) {
    task_power_info info;
    if (!GetTaskPowerInfo(&info)) {
      printf("tick: ???");
    } else {
      printf("tick: irpt=%llu, idle=%llu, bin1=%llu, bin2=%llu\n",
             info.task_interrupt_wakeups, info.task_platform_idle_wakeups,
             info.task_timer_wakeups_bin_1, info.task_timer_wakeups_bin_2);
    }
    fflush(stdout); // without this the script swallows the output, somehow
  }
}

int
main(int argc, char* argv[])
{
  if (argc != 2) {
    Error("must provide a frequency argument");
  }
  char* endptr;
  gFreq = strtol(argv[1], &endptr, /* base = */ 10);
  if (*endptr) {
    Error("frequency is not an integer");
  }
  if (gFreq < 2 || gFreq > 1000000) {
    Error("frequency must be in the range 2..1000000");
  }

  // Install the signal handler.
  struct sigaction sa;
  memset(&sa, 0, sizeof(sa));
  sa.sa_sigaction = SigprofHandler;
  sa.sa_flags = SA_RESTART | SA_SIGINFO;
  if (sigemptyset(&sa.sa_mask) < 0) {
    Error("sigemptyset failed");
  }
  if (sigaction(SIGALRM, &sa, NULL) < 0) {
    Error("sigaction failed");
  }

  // Set up the timer.
  struct itimerval timer;
  timer.it_interval.tv_sec = 0;
  timer.it_interval.tv_usec = 1000000 / gFreq;
  timer.it_value = timer.it_interval;
  if (setitimer(ITIMER_REAL, &timer, NULL) < 0) {
    Error("setitimer failed");
  }

  while (true) {
    pause();
  }

  return 0;
}