Converting "create_task"

[Zingam]

How do I convert this code from the default UWP project. I cannot get the continuations right according to the compiler:

        // Function that reads from a binary file asynchronously.
	inline Concurrency::task<std::vector<byte>> ReadDataAsync(const std::wstring& filename)
	{
		using namespace Windows::Storage;
		using namespace Concurrency;

		auto folder = Windows::ApplicationModel::Package::Current->InstalledLocation;

		return create_task(folder->GetFileAsync(Platform::StringReference(filename.c_str()))).then([] (StorageFile^ file) 
		{
			return FileIO::ReadBufferAsync(file);
		}).then([] (Streams::IBuffer^ fileBuffer) -> std::vector<byte> 
		{
			std::vector<byte> returnBuffer;
			returnBuffer.resize(fileBuffer->Length);
			Streams::DataReader::FromBuffer(fileBuffer)->ReadBytes(Platform::ArrayReference<byte>(returnBuffer.data(), fileBuffer->Length));
			return returnBuffer;
		});
	}

Here is my sorry attempt:

        return create_task(folder.GetFileAsync(winrt::hstring_ref(filename.c_str()))).then([](StorageFile const& file)
        {
            return FileIO::ReadBufferAsync(file);
        //}).then([] (Streams::IBuffer^ fileBuffer) -> std::vector<byte>
        }).then([](Streams::IBuffer const& fileBuffer)->std::vector<byte>
        {
            std::vector<byte> returnBuffer;
            //returnBuffer.resize(fileBuffer->Length);
            returnBuffer.resize(fileBuffer.Length());
            //Streams::DataReader::FromBuffer(fileBuffer)->ReadBytes(Platform::ArrayReference<byte>(returnBuffer.data(), fileBuffer->Length));
            Streams::DataReader::FromBuffer(fileBuffer).ReadBytes(winrt::array_ref<byte>(returnBuffer));
            return returnBuffer;
        });

[kennykerr]

There are a number of problems with using PPL, not the least of which is the difficulty in debugging stuff like this. Have you tried using coroutines? We have found that porting existing PPL code directly to C++ coroutines is quite a lot simpler.

[Zingam]

I haven't implemented that code above still as I have trouble getting co_await to compile in the original sample from VS2015. It doesn't even recognize the co_await keyword but other samples compile and run.

So I decided to try VS2017 and to copy line by line the code from the original C++/CX DX11 sample and to convert it to C++/WinRT on the go. So I have yet to reach that code above.

Meanwhile: If ppl is to be removed how is one supposed to write code like that:

	SuspendingDeferral^ deferral = args->SuspendingOperation->GetDeferral();
	create_task([this, deferral]()
	{
                m_deviceResources->Trim();
		// Insert your code here.
		deferral->Complete();
	}); 

Well I actually did this:

	uwp::SuspendingDeferral const& deferral = args.SuspendingOperation().GetDeferral();
	auto completeDeferral =
		[this, deferral]()
	{
		//m_deviceResources.Trim();
		// Insert your code here.
		deferral.Complete();
	};
	// A new thread is launched to execute the task asynchronously
	std::async(std::launch::async, completeDeferral);

The sample doesn't work properly with the default std::async() parameter values. I need to use std::launch::async.

My concern is what if corotines don't get accepted into the standard?

[kennykerr]

If you're not comfortable with adopting coroutines just yet then you're free to use the standard thread support library or roll your own.