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Creating an async task with a timeout

Question

I came up with this (untested) way of creating a async operation with timeout:

   cancellation_token_source cancelTokenSource;
    task<int> writeTask = create_task(outStream->WriteAsync(buffer))
    .then([size](DWORD written) {
      return outStream->FlushAsync();
    }).then([](bool) {
      return 1;
    }, cancelTokenSource.get_token());
    task<int> timeoutTask = create_task([timeout, cancelTokenSource](){
      std::this_thread::sleep_for(std::chrono::milliseconds(timeout));
      try {
        cancelTokenSource.cancel();
      } catch (Exception^ e) {
        e->Message;
      }
      return -1;
    });
    auto tasks = writeTask || timeoutTask;
    try {
      return tasks.get();
    }
    catch (Exception^ e) {
      e->Message;
    }

The timeout thread just idles and then cancels the real task (that reads from a socket).

Is this guaranteed to work always? Or can there be a race condition when the timeoutTask wants to trigger the cancelTokenSource.cancel() method and the real task just finished?

Are there any other (more generic) ways (like a create_task_with_timeout) out there?

Friday, July 11, 2014 1:00 AM

Answers

Hi,

You can use:

 
WaitForSingleObjectEx(smi_event_wait,1000,false);

it can sleep 1 second and add a cancellation taken in the constructor then cancel the task:

 task<void>(create_async([]() {		
		auto s = ref new StreamSocket();

		/*
		 * Connect to host
		 */
		task<void>(s->ConnectAsync(ref new HostName(ref new Platform::String(L"google.com")), ref new Platform::String(L"80"))).get();

		auto reader = ref new DataReader(s->InputStream);

		cancellation_token_source read_operation;

		WRL::Wrappers::Event evt(CreateEventExW(NULL, NULL, CREATE_EVENT_MANUAL_RESET, EVENT_ALL_ACCESS));

		/*
		 * Start reading
		 */
		task<unsigned int>(reader->LoadAsync(100), read_operation.get_token()).then([&evt](task<unsigned int> t){
			try
			{
				unsigned int num_read = t.get();				
			}			
			catch (...)
			{
			}
			SetEvent(evt.Get());
		});
		
		WaitForSingleObjectEx(evt.Get(), 1000, FALSE);

		/*
		 * Cancel the operation after 2 seconds of wait
		 */
		read_operation.cancel();

		 FALSE);
	})).then([](task<void> t) {});

You can refer to the link below:

http://msdn.microsoft.com/en-us/library/windows/apps/dd984117.aspx#tasks

Best Wishes!

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Marked as answer by Anne Jing Monday, July 21, 2014 1:24 AM

Monday, July 14, 2014 8:55 AM

Answered by:

Creating an async task with a timeout

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