gcc tight loop measure

timeTest.cpp

#include <iostream>
#include <chrono>
#include <thread>
#include <atomic>

using namespace std::literals;

// compile command
// g++ -lpthread -std=c++14 -march=native -O3 timeTest.cpp -o timeTest

// use thread safe increment this value each ms
std::atomic_int_fast64_t g_milliseconds(0);


static int runclock() {
  auto timeout = std::chrono::high_resolution_clock::now();
  while (1) {
    std::this_thread::sleep_for(1ms);
    auto now = std::chrono::high_resolution_clock::now();
    while (timeout < now) {
      g_milliseconds++;
      timeout += 1ms;
    }
  }
}
static std::uint_fast64_t get_ms_time() { return g_milliseconds; }

int main() {
  std::thread t1(runclock);
  uint_fast64_t times = 0;
  while (get_ms_time() == 0) {
    // wait timer to start running
    std::this_thread::sleep_for(1ms);
  }
  auto lastTime = get_ms_time();
  while (1) {
    auto now = get_ms_time();
    if (now <= lastTime) {
      times++;
    } else {
      std::cout << times << "\r";
      times = 0;
      lastTime = now;
    }
  }
}