C++ Call once sample 1

callonce1.cpp

#include <iostream>
#include <string>
#include <thread>
#include <vector>
#include <mutex> // call once
#include <chrono>

namespace game {

	using namespace std::literals::chrono_literals;

	struct GameResource {
		std::string name;
	};

	std::once_flag isGameResourcesInitialized{};

	std::vector<GameResource> gameResources;

	void initializeResources() {
		bool canThrowException = true;
		std::call_once(isGameResourcesInitialized, [](bool canThrowException) {
			gameResources.push_back({ "resource_one" });
			gameResources.push_back({ "resource_two" });
			std::cout << "Game resources initialized" << std::endl;
		}, canThrowException);
	}

	std::thread startGameThread() {
		initializeResources();
		return std::thread([]() {
			std::thread::id id = std::this_thread::get_id();
			std::cout << "Starting game thread with id: " << id << std::endl;
			std::cout << "Resources: " << std::endl;
			
			for (GameResource& r : gameResources) {
				std::cout << r.name << " from thread " << id << std::endl;
			}

			std::this_thread::sleep_for(3s);
		});
	}

	void updateGameState() {
		std::cout << "Updating some game state..." << std::endl;
	}
}

int main()
{
	std::thread threadOne = game::startGameThread();
	std::thread threadTwo = game::startGameThread();
	std::thread threadThree = game::startGameThread();

	threadOne.join();
	threadTwo.join();
	threadThree.join();
}