Notification.promise --> [reject|resolve] nondeterministic behavior

[gplasky]

Description

I'm building a Jupyter frontend extension and I've created an in-progress notification for an async function similar to what's described in the notification example.

It works well but in my testing I've discovered what I believe is an edge case: The on-screen toast for the in-progress notification doesn't get updated despite the .reject() firing and the reject notification appearing in the notification center (instead of updating the on-screen toast). It appears to only happen once after the initial page load.

Reproduce

1. Load Jupyterlab with my extension enabled and auto-activated.
2. Trigger an in-progress notification with Notification.promise(PromiseDelegate, ...) that then instantly gets rejected with <PromiseDelegate>.reject(...) (e.g. in my case from an async function making an HTTP call which rejects its promise due to ERR_CONNECTION_REFUSED).
3. Observe the in-progress toast remains on screen without displaying the expected error from Notification.reject() [1]
4. Observe the toast in Step 3 continues to remain on-screen.
5. Observe that the Notification.reject() notification is actually shown in the notification center. [2]

[1]

[2]

Expected behavior

1. Load Jupyterlab with my extension enabled and auto-activated.
2. Trigger an in-progress notification with Notification.promise(PromiseDelegate, ...) that then instantly gets rejected (e.g. in my case due to the async function rejecting its promise due to ERR_CONNECTION_REFUSED) with <PromiseDelegate>.reject(...).
3. Observe the in-progress notification update to display an error. [3]

[3]

Context

While this only happens on the first in-progress notification after initial page load, there does not appear to be any correlation with how long after page load this happens. I've been able to reproduce it immediately after page load as well as a number of minutes afterward. After the first time it happens, successive (immediate) failures, as described above, successfully update the in-progress notification as expected.

Workaround

Introducing an artificial delay immediately before the PromiseDelegate.reject(...) call successfully prevents this issue (100ms seems to suffice). This leads me to believe there is something with the Notification system that is lazy loading or otherwise not immediately initializing.

Example

Initialize the promise

        this._fetchToastPromiseDelegate = new PromiseDelegate<string>;
        Notification.promise(this._fetchToastPromiseDelegate.promise, ...);

Add delay before rejection

        } catch (err) {
            await new Promise(f => setTimeout(f, 100));
            this._fetchToastPromiseDelegate.reject("Error fetching results. Consult the console logs for details.");
            httpErrorHandler(err);

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[JasonWeill]

@gplasky Thank you for opening this issue!