Shared pointer assignment benchmark

shared_ptr_benchmark.cpp

#include <memory>
#include <vector>

#include <chrono>
#include <iostream>

using namespace std;

#define BENCH_COUNT 10000000

// benchmark for checking whether shared_ptr is equal before assigning

// shared pointer assignment benchmark
// M1 macbook (clang++):
// Shared pointer assignment (equal)
// Without check: 86ms
// With check: 7ms

// Shared pointer assignment (not equal)
// Without check: 85ms
// With check: 86ms

template<class T>
void AssignSharedPointer(shared_ptr<T> &target, const shared_ptr<T> &source) {
	if (target.get() != source.get()) {
		target = source;
	}
}

int main() {

	// allocate shared pointers
	vector<shared_ptr<int>> shared_bank;
	vector<shared_ptr<int>> assign;
	for(size_t i = 0; i < BENCH_COUNT; i++) {
		shared_bank.push_back(make_shared<int>(i));
		assign.push_back(shared_bank[i]);
	}

	// dry run
	for(size_t i = 0; i < BENCH_COUNT; i++) {
		assign[i] = shared_bank[i];
	}

	std::cout << "Shared pointer assignment (equal)\n";

	auto start =chrono::system_clock::now();
	for(size_t i = 0; i < BENCH_COUNT; i++) {
		assign[i] = shared_bank[i];
	}
	auto end = chrono::system_clock::now();

	auto elapsed =
		std::chrono::duration_cast<std::chrono::milliseconds>(end - start);
	std::cout << "Without check: " << elapsed.count() << "ms\n";

	start =chrono::system_clock::now();
	for(size_t i = 0; i < BENCH_COUNT; i++) {
		AssignSharedPointer(assign[i], shared_bank[i]);
	}
	end = chrono::system_clock::now();

	elapsed =
		std::chrono::duration_cast<std::chrono::milliseconds>(end - start);
	std::cout << "With check: " << elapsed.count() << "ms\n";


	std::cout << "Shared pointer assignment (not equal)\n";

	// reset
	for(size_t i = 0; i < BENCH_COUNT - 1; i++) {
		assign[i] = shared_bank[i + 1];
	}

	start =chrono::system_clock::now();
	for(size_t i = 0; i < BENCH_COUNT - 1; i++) {
		assign[i] = shared_bank[i];
	}
	end = chrono::system_clock::now();

	elapsed =
		std::chrono::duration_cast<std::chrono::milliseconds>(end - start);
	std::cout << "Without check: " << elapsed.count() << "ms\n";

	// reset
	for(size_t i = 0; i < BENCH_COUNT - 1; i++) {
		assign[i] = shared_bank[i + 1];
	}

	start =chrono::system_clock::now();
	for(size_t i = 0; i < BENCH_COUNT; i++) {
		AssignSharedPointer(assign[i], shared_bank[i]);
	}
	end = chrono::system_clock::now();

	elapsed =
		std::chrono::duration_cast<std::chrono::milliseconds>(end - start);
	std::cout << "With check: " << elapsed.count() << "ms\n";

}