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Request: invalidation should resolve when a cell throws an error

#1

Observable’s invalidation promise currently does not resolve when the corresponding cell throws an error:

It only resolves if / when the errored cell is re-evaluated. I would like it to resolve immediately upon rejection as this would make it easier for me to keep track of “live” cells in a notebook I’m working on where some of the cells are communicating with a cell that acts like a “server”.

#2

This is also true of generator cells: the invalidation promise doesn’t resolve greedily after the generator returns; it waits until the cell is re-run.

{
  invalidation.then(() => console.log("invalidated"));
  for (let i = 0; i < 10; ++i) {
    yield i;
  }
}

We wouldn’t want to change that behavior because there are many cases where Observable isn’t aware that a cell is still “running” (e.g., in a requestAnimationFrame loop rather than a generator loop), but it’s still useful to handle invalidation when a cell is re-run.

That said, it might still be okay to invalidate greedily on error, since it’s a bit weird to allow the cell to continue to run when it’s showing an error.

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#3

Resolving on error sounds reasonable.

Unrelated: a search of observable for invalidation turns up page after page of really great notebooks.

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