Support for future cancellation

[tbekas]

The Future[T] api supports cancelling, so it would be nice to propagate this cancellation to the submitted task, if the task didn't start already executing. Probably nim-taskpools doesn't allow that, but maybe we could achieve it anyway by doing additional check at the beginning of the task to see if it wasn't cancelled, if it was, return immediately instead of doing possibly an expensive computation.

[elcritch]

100%, I was planning out how to do it this morning. There's some details with how to do it.

Probably nim-taskpools doesn't allow that, but maybe we could achieve it anyway by doing additional check at the beginning of the task to see if it wasn't cancelled,

Taskpools doesn't support cancellation like that. However, the check at the beginning or other points would make sense. There's details on how to handle it, but likely using an atomic to mark it.

The other biggest question would be the API for it. Maybe just a check in jobs before it calls the task proc?

[elcritch]

Ok, got the memory stuff sorted in #6. So now I can work on adding cancellation support.