Task cancellation in VS2010 version

Question

First I would like to express my thanks to the team for making PPL tasks available for those of us who must stick with VS2010 C++ compiler for a while.

They work great for me so far.

One minor detail: this code below wouldn't compile because interruption_point and is_task_cancellation_requested functions could not be found:

void PrintStuff()
{
   while(true)
   {
      //interruption_point();
      //if(is_task_cancellation_requested())
      //{
      //   cancel_current_task();
      //}
      std::cout << '.';
   }

   std::cout << std::endl;
}

I am able to work  around these issues by passing cancellation token as a parameter to function. I wonder if I am missing something, or are these functions indeed not implemented, for whatever reason?

In fact, I am not sure that I understand how to create a cancellable task, short of creating an external cancellation token and capturing it in task's lambda.

 

Answer 1

Tonko,

Thanks for the kind words!

The pplx namespace that you see in Casablanca is the beginning of our effort to make PPL platform- and compiler-independent. For now, we ported just enough of the PPL to support asynchronous operations for Casablanca, but not the parts of the PPL that rely on the task_group class, such as the parallel_for and other parallel algorithms.

The APIs you mentioned are useful when combining PPL tasks with the task_group-based parallel algorithms that do not support cancellation tokens.

If you only use PPL tasks and not other PPL algorithms, cancellation tokens is a great way to go. We like them for their explicitness - cancellation tokens make it very clear how the cancellation is requested, how it's propagated to other tasks, and what tasks react to them.

So what you call a work around is actually a perfectly fine way of doing it!

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Artur Laksberg Visual C++ Team Microsoft