c++ async multiple tasks implementation

Question

I have used the tasks in c# in this way:

static async Task<string> DoTaskAsync(string name, int timeout)
{
   var start = DateTime.Now;
   Console.WriteLine("Enter {0}, {1}", name, timeout);
   await Task.Delay(timeout);
   Console.WriteLine("Exit {0}, {1}", name, (DateTime.Now - start).TotalMilliseconds);
   return name;
}

public Task DoSomethingAsync()
{
    var t1 = DoTaskAsync("t2.1", 3000);
    var t2 = DoTaskAsync("t2.2", 2000);
    var t3 = DoTaskAsync("t2.3", 1000);

    return Task.WhenAll(t1, t2, t3);
}

but I need to do the some in c++.

There is a way to migrate this code in c++ ?

Thanks !

There are several options for a direct translation, but rarely is a direct translation the right solution. Instead assess the behaviour you want on a grander scale and see if C++ offers a different path to attaining it that will serve your goals better. — user4581301
– user4581301, Commented Sep 14, 2022 at 18:56

Ted Lyngmo · Accepted Answer · 2022-09-14 19:57:48Z

4

A more or less direct translation would probably use C++ std::futures returned by std::async.

Disclaimer: I don't have bit of C# knowledge and just read about its Tasks a bit just now. I think this is what you are going for.

In C++ we use std::chrono::durations instead of plain ints. The resolution of the clocks is often much higher than milliseconds, so I selected to go for whatever duration the std::chrono::steady_clock supports. You can thereby pass it a std::chrono::milliseconds or std::chrono::seconds - and it will do the right thing.

#include <array>
#include <chrono>    // clocks and durations
#include <format>    // std::format
#include <future>    // std::async
#include <iostream>
#include <string>
#include <thread>    // std::this_thread::sleep_for

auto DoTaskAsync(std::string name, std::chrono::steady_clock::duration timeout)
{
    return std::async(std::launch::async,
        [name=std::move(name),timeout] {
            auto start = std::chrono::steady_clock::now();
            std::cout << std::format("Enter {0}, {1}\n", name, timeout);

            std::this_thread::sleep_for(timeout);
            
            std::cout << std::format("Exit {0}, {1}\n", name,
                std::chrono::duration_cast<std::chrono::milliseconds>(
                    std::chrono::steady_clock::now() - start));
            
            return name;
        });
}

std::array<std::string, 3> DoSomethingAsync() {
    using namespace std::chrono_literals;
    auto t1 = DoTaskAsync("t2.1", 3000000000ns); // nanoseconds
    auto t2 = DoTaskAsync("t2.2", 2000ms);       // milliseconds
    auto t3 = DoTaskAsync("t2.3", 1s);           // seconds
    return {t1.get(), t2.get(), t3.get()};
}

Demo

edited Sep 14, 2022 at 19:57

answered Sep 14, 2022 at 19:38

Ted Lyngmo

124k7 gold badges93 silver badges155 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

user4581301 Over a year ago

Side note: You have to be compiling against the C++20 Standard to get all the goodies used here, so at this time you'll need a fairly up-to-date compiler and almost certainly have to select C++20 with a compiler option.

Ted Lyngmo Over a year ago

@user4581301 Absolutely. I wanted to stay as close to OPs code as possible so I threw things in that my normal compiler doesn't even support. At least MSVC supports it all. It's probably not long before the other vendors catch up. :-) C++20 should be default for any new project though so I don't see that as a big problem.

user4581301 Over a year ago

Still clawing my way up to C++17 as the minimum for new projects. Tooling for some of the stuff I work on is sparse.

Ted Lyngmo Over a year ago

@user4581301 Tell me about it. I have to fight gcc 4.7.3 on a daily basis. It doesn't even know thread_local, much less C++17.

marcoluca987 Over a year ago

Thank you this is what I need. However I have C++17. The content of DoTaskAsync is only and example can be only Print("Hello word"). There is a way to extend compatibility with C++17 ?

|

Collectives™ on Stack Overflow

c++ async multiple tasks implementation

1 Answer 1

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related