1#include <inttypes.h>
2#include <sys/types.h>
3#include <time.h>
4#include <unistd.h>
5
6#define noinline __attribute__((__noinline__))
7
8static inline uint64_t GetSystemClock() {
9  timespec ts;
10  // Assume clock_gettime() doesn't fail.
11  clock_gettime(CLOCK_MONOTONIC, &ts);
12  return ts.tv_sec * 1000000000ULL + ts.tv_nsec;
13}
14
15constexpr int LOOP_COUNT = 100000000;
16uint64_t noinline RunFunction() {
17  uint64_t start_time_in_ns = GetSystemClock();
18  for (volatile int i = 0; i < LOOP_COUNT; ++i) {
19  }
20  return GetSystemClock() - start_time_in_ns;
21}
22
23uint64_t noinline SleepFunction(unsigned long long sleep_time_in_ns) {
24  uint64_t start_time_in_ns = GetSystemClock();
25  struct timespec req;
26  req.tv_sec = sleep_time_in_ns / 1000000000;
27  req.tv_nsec = sleep_time_in_ns % 1000000000;
28  nanosleep(&req, nullptr);
29  return GetSystemClock() - start_time_in_ns;
30}
31
32void noinline GlobalFunction() {
33  uint64_t total_sleep_time_in_ns = 0;
34  uint64_t total_run_time_in_ns = 0;
35  while (true) {
36    total_run_time_in_ns += RunFunction();
37    if (total_sleep_time_in_ns < total_run_time_in_ns) {
38      total_sleep_time_in_ns += SleepFunction(total_run_time_in_ns - total_sleep_time_in_ns);
39    }
40  }
41}
42
43int main() {
44  GlobalFunction();
45  return 0;
46}
47