Cancelling a Windows Runtime asynchronous operation, part 4: C++/CX with PPL, coroutine style with raw IAsyncAction and IAsyncOperation

Raymond Chen

Last time, we looked at how task cancellation is projected in C++/CX with PPL and co_await with tasks. But PPL also supports awaiting directly on IAsyncAction^ and IAsyncOperation^ objects. Let’s try it.

auto picker = ref new FileOpenPicker();

auto pickerOp = picker->PickSingleFileAsync();
cancellation_token_source cts;
call<bool> do_cancel([pickerOp](bool) { pickerOp.Cancel(); });
timer<bool> delayed_cancel(3000U, false, &do_cancel);

StorageFile^ file;
try {
    file = co_await pickerOp;
} catch (OperationCanceledException^) {
    file = nullptr;

if (file != nullptr) {

Observe that awaiting directly on an IAsyncAction^ and IAsyncOperation^ object throws a different exception from awaiting on a task.

You can see this in the await_resume for the IAsyncInfo^ awaiter ind in pplawait.h:

template <typename _TaskTy, typename _HandlerTy>
struct _IAsync_awaiter {

    auto await_resume() {
        return _Task->GetResults();

void _VerifyStateForResultsCall(
    Windows::Foundation::AsyncStatus _Status)
    if (_Status == AsyncStatus::Canceled) {
        throw ::Platform::Exception::CreateException(E_ABORT);

The PPL framework checks whether the status of the async operation is Canceled, and if so, it throws E_ABORT, which is represented in C++/CX as Operation­Canceled­Exception.

So far, all of the cancellation exceptions have generated by the framework. That’ll change soon. Next time, we’ll look at C++/WinRT.

1 comment

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  • Mystery Man 0

    I’m curious. How do your Microsoft colleges pronounce PPL? Like “People”?

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