Reset execution indicator state when kernel restarts

[krassowski]

References

Fixes #13780.

Code changes

Add special handling for restarting message, which is the only message we get if the kernel is killed non-gracefully. Because abrupt killing of kernel prevents it from responding with idle status we need to listen to restarting instead (and clear the set with scheduled cells).

User-facing changes

Execution indicator works after abrupt kernel death.

Backwards-incompatible changes

None

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[krassowski]

The added test is a bit blunt and while it works perfectly locally it does not pass on CI.

I did not find another way to reproduce the issue with a two-liner, but suggestions for an alternative testing strategy (or how to make the tests pass) are very much welcome!

[krassowski]

I was able to reproduce the CI error locally; it was because previously I was only running the added test in isolation; as it was killing kernel we had to restart it. This was fixed in 40acbf2.

For record the traceback when tests were failing was:

Traceback (most recent call last):
  File "tornado/web.py", line 1713, in _execute
    result = await result
  File "jupyter_server/services/sessions/handlers.py", line 190, in delete
    await sm.delete_session(session_id)
  File "jupyter_server/services/sessions/sessionmanager.py", line 523, in delete_session
    await ensure_async(self.kernel_manager.shutdown_kernel(session["kernel"]["id"]))
  File "jupyter_core/utils/__init__.py", line 172, in ensure_async
    result = await obj
  File "jupyter_server/services/kernels/kernelmanager.py", line 426, in _async_shutdown_kernel
    return await self.pinned_superclass._async_shutdown_kernel(
  File "jupyter_client/multikernelmanager.py", line 264, in _async_shutdown_kernel
    if not km.ready.cancelled() and km.ready.exception():
asyncio.exceptions.InvalidStateError: Exception is not set.

[trungleduc]

Thanks @krassowski!

[fcollonval]

@meeseeksdev please backport to 3.6.x

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 3.6.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 98e684cfbe8982b65d9ea518ccb9801762cc8a8a

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #13832: Reset execution indicator state when kernel restarts'

4. Push to a named branch:

git push YOURFORK 3.6.x:auto-backport-of-pr-13832-on-3.6.x

5. Create a PR against branch 3.6.x, I would have named this PR:

"Backport PR #13832 on branch 3.6.x (Reset execution indicator state when kernel restarts)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.