How to implement when_all for list of IAsyncOperation<TResult>

Question

As in the title: How to implement a method similar to concurrency::when_all for list of IAsyncOperation?

Best regards, Michał

Answer 1

Based on this thread, you can define a when_all template manually. But it needs you to pass each task as a parameter.

Update:

If you want to put a vector of IAsyncAction in when_all method, you can refer to this thread. For example:

MainPage.h

template <typename T>
Windows::Foundation::IAsyncAction when_each(T first, T last)
{
    for (; first != last; ++first)
    {
        co_await *first;
    }
}

struct MainPage : MainPageT<MainPage>
{
    MainPage();

    Windows::Foundation::IAsyncAction wait_for(Windows::Foundation::TimeSpan duration);

    Windows::Foundation::IAsyncAction ClickHandler(Windows::Foundation::IInspectable const& sender, Windows::UI::Xaml::RoutedEventArgs const& args);
};

MainPage.cpp:

#include <debugapi.h>

using namespace winrt;
using namespace Windows::UI::Xaml;
using namespace std::chrono;

Windows::Foundation::IAsyncAction MainPage::wait_for(Windows::Foundation::TimeSpan duration)
{
    co_await duration;
    hstring formattedText = L"done" + to_hstring(duration.count());
    OutputDebugString(formattedText.c_str());
}

Windows::Foundation::IAsyncAction MainPage::ClickHandler(IInspectable const&, RoutedEventArgs const&)
{
    std::vector v{ wait_for(4s), wait_for(2s), wait_for(3s) };
    co_await when_each(v.begin(), v.end());
}

The result of output:

done 20000000 done 30000000​ done 40000000

Then you can replace wait_for method with your async operations to achieve it.