mutex-atomic.cc

#include <iostream>
#include <chrono>
#include <atomic>
#include <cassert>
#include <mutex>

const int ITERATIONS = 10'000'000;

std::mutex mtx;
int state = 2;
std::atomic<int> atomic_state{2};

void do_something();

void mutex_bench() {

	for (int i=0; i<ITERATIONS; i++) {
		{
			std::lock_guard<std::mutex> guard(mtx);
			assert(state == 2);
			state = 1;
		}

		do_something();

		{
			std::lock_guard<std::mutex> guard(mtx);
			assert(state == 1);
			state = 2;
		}
	}
}

void atomic_bench() {

	for (int i=0; i<ITERATIONS; i++) {
		{
			int expected = 2;
			atomic_state.compare_exchange_weak(expected, 1, std::memory_order_relaxed, std::memory_order_relaxed);
			assert(expected == 2);
		}

		do_something();

		{
			int expected = 1;
			atomic_state.compare_exchange_weak(expected, 2, std::memory_order_relaxed, std::memory_order_relaxed);
			assert(expected == 1);
		}
	}
}

int main() {
	auto start = std::chrono::steady_clock::now();
	mutex_bench();
	auto middle = std::chrono::steady_clock::now();
	atomic_bench();
	auto end = std::chrono::steady_clock::now();
	std::cout << "mutex:  " << std::chrono::duration_cast<std::chrono::milliseconds>(middle - start).count() << "[ms]" << std::endl;
	std::cout << "atomic: " << std::chrono::duration_cast<std::chrono::milliseconds> (end - middle).count() << "[ms]" << std::endl;
	return 0;
}