main.cpp

#include <iostream>       
#include <thread>         
#include <future>         
#include <stdexcept>   
#include <chrono>
#include <mutex>

/******************************* Example 1 ******************************/
void print_result1(std::future<int>& fut)
{
	//std::cout << fut.get() << "\n";
	if (fut.valid())
	{
		std::cout << "this is valid future\n";
		std::cout << fut.get() << "\n";
	}
	else
	{
		std::cout << "this is invalid future\n";
	}
}

void run_code1()
{
	std::promise<int> prom;
	std::future<int> fut(prom.get_future());

	std::thread th1(print_result1, std::ref(fut));
	std::thread th2(print_result1, std::ref(fut));

	prom.set_value(5);

	th1.join();
	th2.join();
}

/************************************* Example 2 **************************************/

void print_result2(std::shared_future<int>& fut)
{
	std::cout << fut.get() << "  - valid future \n";
}

void run_code2()
{
	std::promise<int> prom;
	std::shared_future<int> fut(prom.get_future());

	std::thread th1(print_result2, std::ref(fut));
	std::thread th2(print_result2, std::ref(fut));

	prom.set_value(5);

	th1.join();
	th2.join();
}

int main()
{
	run_code1();
	run_code2();

	return 0;
}