Asynchronous features (async, promises, futures)

async.cpp

#include <iostream>
#include <future>
#include <thread>

std::mutex mu;

template <typename T>
void print(std::string message, T data)
{
    std::lock_guard<std::mutex> lg(mu);
    std::cout << message << data << std::endl;
}

int computation(int arg)
{
    print("computation begins for ", arg);
    std::this_thread::sleep_for(std::chrono::seconds(1));
    print("computation ends for ", arg);
    return 2 * arg + 1;
}

int action(std::future<int> fu)
{
    print("action got ", fu.get());
    return 0;
}

int main()
{
    std::future<int> fu1 = std::async(std::launch::deferred , computation, 1010);
    std::future<int> fu2 = std::async(std::launch::deferred , computation, 1020);
    std::future<int> fu3 = std::async(std::launch::deferred , computation, 1030);

    print("********** ", " started");

    std::async(std::launch::async, action, std::move(fu1)).get();
    std::async(std::launch::async, action, std::move(fu2)).get();
    std::async(std::launch::async, action, std::move(fu3)).get();

    print("********** ", " completed");
}