Asynchronous HTTP requests with co_await - c++

Question

I have multiple std::functions that are called on the main thread (not on different threads) in my app (as the result of an asynchronous HTTP requests), for example:
namespace model { struct Order{}; struct Trade{};}
std::function<void (std::string)> func1 = [](std::string http_answer)
{
std::vector<model::Order> orders = ParseOrders(http_answer);
std::cout << "Fetched " << orders.size() << " open/closed orders.");
}
std::function<void (std::string)> func2 = [](std::string http_answer)
{
std::vector<model::Trade> trades = ParseTrades(http_answer);
std::cout << "Fetched " << trades.size() << " trades.");
}
How to call process_result when the both func1 and func2 have parsed HTTP answers?
auto process_result = [](std::vector<model::Order> orders, std::vector<model::Trades> trades)
{
std::cout << "Matching orders and trades.";
};
Is there some solution with co_await or something like this?

Answer 1

You need some kind of synchronization point. Have not used co_await so far so this might not be what you are looking for, however in c++17 I'd go for a std::promise / std::future, maybe like this:
#include <iostream>
#include <functional>
#include <future>
std::promise<std::string> p1;
std::function<void (std::string)> func1 = [](std::string http_answer)
{
// std::vector<model::Order> orders = ParseOrders(http_answer);
// std::cout << "Fetched " << orders.size() << " open/closed orders.");
p1.set_value(http_answer);
};
std::promise<std::string> p2;
std::function<void (std::string)> func2 = [](std::string http_answer)
{
// std::vector<model::Trade> trades = ParseTrades(http_answer);
// std::cout << "Fetched " << trades.size() << " trades.");
p2.set_value(http_answer);
};
int main () {
// whenever that happens...
func1("foo");
func2("bar");
// synchronize on func1 and func2 finished
auto answer1 = p1.get_future().get();
auto answer2 = p2.get_future().get();
auto process_result = [&](/* std::vector<model::Order> orders, std::vector<model::Trades> trades */)
{
std::cout << "Matching orders and trades... " << answer1 << answer2;
};
process_result();
return 0;
}
http://coliru.stacked-crooked.com/a/3c74f00125999fb6
https://en.cppreference.com/w/cpp/thread/future