fix: cancelled instances hanging indefinitely

[paoloricciuti]

Closes #93 and probably #94 too

Pretty nasty bug: when cancelled we need to resolve the promise in some way or it will hang indefinitely. This was shown in task types that were waiting for the old one to finish but it was a general bug.

For the moment i've opted into rejecting the promise with a Custom Error so that the user can check against that instance if the task has been cancelled. This feels the right thing to do but i would love your opinion on this when you are back from vacation @beerinho @nickschot

I also realized that we were doing something wrong with the restart so i moved the array to be a set and removed that specific instance instead of popping the array.

[nickschot]

If I understand correctly, this is what's known as a cancellation error in ember-concurrency. There's a util available called didCancel to allow the user to check that. https://github.com/machty/ember-concurrency/blob/master/packages/ember-concurrency/src/-private/external/task-instance/cancelation.js#L23

[paoloricciuti]

If I understand correctly, this is what's known as a cancellation error in ember-concurrency. There's a util available called didCancel to allow the user to check that. https://github.com/machty/ember-concurrency/blob/master/packages/ember-concurrency/src/-private/external/task-instance/cancelation.js#L23

Yes...i thought of adding an helper too but at the end of the day the user can always check with instanceof. We can provide the helper too but maybe i would do it in a separate PR.

[beerinho]

Yes...i thought of adding an helper too but at the end of the day the user can always check with instanceof. We can provide the helper too but maybe i would do it in a separate PR.

I prefer the idea of having a helper attached to the task instance over the requirement to import the CancellationError and checking if it's an instanceof. I've created a task for it here - #101