promiseDemo.cpp

// promise example
#include <iostream> // std::cout
#include <functional> // std::ref
#include <thread> // std::thread
#include <future> // std::promise, std::future
void print_int(std::future<int>& fut) {
	// Thread waits here untill the promise value is set
	int x = fut.get();
	std::cout << "value: " << x << '\n';
}
int main()
{
	std::promise<int> prom; // create promise
	std::future<int> fut = prom.get_future(); // engagement with future
	// Make sure to pass the fut as reference and not value
	std::thread th1(print_int, std::ref(fut)); // send future to new thread
	// Untill the value is set, the above thread will be waiting
	prom.set_value(10); // fulfill promise
	//(synchronizes with getting the future)
	th1.join();
	return 0;
}