Perform async task before saving notebook

[maartenbreddels]

Hi all,

I am trying to implement saving extra content in mime bundle in cell output on document saving in jupyter-widgets/ipywidgets#3107 . For this I was planning to use context.saveState.connect((sender, saveState) => ... but looking at

jupyterlab/packages/docregistry/src/context.ts

Line 506 in c91e1ea

this._saveState.emit('started');

I see that the event is emitted, and not awaited for.

This makes it impossible to do async tasks before saving the document. I was wondering if this is a design decision or a possible oversight, or simply not implemented.

cheers,

Maarten

[jasongrout]

I see that the event is emitted, and not awaited for.

You cannot await a signal emission: https://github.com/jupyterlab/lumino/blob/4f2432290e874b040310d428593abe4afc336066/packages/signaling/src/index.ts#L187-L189

[jasongrout]

For reference (for others reading this), we hook into the signal to do synchronous tasks in ipywidgets around saving state: https://github.com/jupyter-widgets/ipywidgets/blob/c46e5dc306b7a908f749ede13392d8bdc5379821/jupyterlab_widgets/src/manager.ts#L524-L528

[maartenbreddels]

That explains the _modelsSync and get_state_sync.

Do you think it is useful to have the option to perform async work before saving?