Cancel state

[cicdw]

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• adds new tests (if appropriate)
• updates CHANGELOG.md (if appropriate)
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What does this PR change?

This PR:

• renames Aborted state Cancelled
• introduces graceful translation of KeyboardInterrupts to Cancelled states when running Flows in Core
• introduces heartbeat check in Cloud to look for cancelled flow runs and respond via cancelled states / termination of execution

Why is this PR important?

Core users will immediately see the benefit of CTRL+C when running flow.run, and this will soon enable the ability to cancel flow runs from the UI once the new state serializers have made their way to Prod.

[codecov]

Codecov Report

Merging #1758 into master will decrease coverage by 0.1%.
The diff coverage is 51.92%.

[joshmeek]

🚀

I reject my review because I'm not sure if it should be Cancelled or Canceled

[jlowin]

Do cancelled states result in downstream triggerfails or possibly downstream runs if they have on failed triggers? Should a cancelled task not be followed by any task runs?

(Not a leading question, just asking. I can imagine cancelling a task and WANTING downstream cleanups to run)

[cicdw]

Great question @jlowin - because we will only support cancellation of at the Flow Run level, downstream tasks will never be able to enter a Running state. This is because once the Flow Run enters a Cancelled state, all heartbeats will fail / raise errors in the main thread. Moreover, once we implement version locking with Flow Run versions as well, downstream tasks won't even be able to change their state as their flow run state version will be out-of-date.

However, there is the potential for some inefficiency when running with Dask - whenever the Flow Run process raises the KeyboardInterrupt, Dask will detect that and "cancel" all Futures associated with that client. I found that in practice all those futures still ran, meaning the very initial task runner pipeline steps will still run for all tasks, but they will never be able to actually update the task run's state.

[jlowin]

Ah, thanks for clearing that up for me.