Check logic around changing kernels in JupyterLab manager

jupyter-widgets / ipywidgets

Interactive Widgets for the Jupyter Notebook

https://ipywidgets.readthedocs.io

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Open jasongrout opened 3 years ago

jasongrout commented 3 years ago

In https://github.com/jupyter-widgets/ipywidgets/commit/9d999d7b267ade8037b821ce356868a3ce205bd8 (part of #2532), we introduced changes refactoring how kernels are used in the JupyterLab manager.

When a session context changes a kernel, is this._kernel reset?
In ipywidgets 7.x, we waited for the context to be ready in _loadFromKernel - is that still done in the refactor, or is it needed?
Consider this comment again: https://github.com/jupyter-widgets/ipywidgets/pull/2532#discussion_r367882710
Consider this comment again: https://github.com/jupyter-widgets/ipywidgets/pull/2532#discussion_r367884298

jtpio commented 3 years ago

When a session context changes a kernel, is this._kernel reset?

Does this question only apply to the KernelWidgetManager?

The WidgetManager (used for notebooks) seems to be handling a SessionContext, which should handle kernel restarts.

So accessing this.kernel should return the current kernel for the session context:

jtpio commented 3 years ago

In ipywidgets 7.x, we waited for the context to be ready in _loadFromKernel - is that still done in the refactor, or is it needed?

Looking at the code, _loadFromKernel seems to be called from the WidgetManager here:

And from KernelWidgetManager here:

With _loadFromKernel defined in the base LabWidgetManager class: