Webview - retainContextWhenHidden

[jmenzies12]

Hey there,

I noticed in your examples that retainContextWhenHidden is set to true when creating the Webview editor provider and changing it to false breaks the diagram functionality (i.e. if you change tab and then come back the diagram will be blank). The VSCode docs warn against using this setting due to performance overhead unless necessary.

We were wondering if you had to turn this on for specific reasons? And whether it would be feasible for us to turn it off and then implement any missing functionality.

Cheers
Jonathan

[tortmayr]

Hi @jmenzies12,

disabling this option means that the diagram editor webview is always disposed when hidden e.g. by switching to another tab.
When the diagram editor tab then is focused again the webview has to be recreated from scratch.
Without any additional improvements for GLSP this would mean that we have to re-initiate the communication to the server and create a new diagram session. This has some severe downsides:

• Loading overhead & potential flickering whenever the tab is made visible again
• The current session on the server side including any pending changes is lost
• The server can no longer communicate with the webview when hidden

Some additional work would be required to make this work properly. After an initial evaluation we ended up with the decision that the retainContextWhenHidden option is an acceptable compromise as the performance overhead is negligible unless you open alot of large diagrams open in parallel.

I agree in the long run a more sophisticated solution without retaining the context would be preferable.
However, this would include a couple of non-trival changes. In particular we require:

• A way to store/cache the current model before destroying the webview. On recreation the cached model can than be used to avoid a roundtrip and/or re initialization of the server. The getState/setState API could probably be used for that.
• The current client/session id of the webview needs to be persisted so that after recreation the existing session on the server can be reused
• A caching mechanism is required to queue any messages from the server while the webview is hidden. Once the webview is recreated the queue can be emptied.

And probably a couple of other issues that we are not even aware of right now.

So while its technically feasible the effort to achieve this is rather high.

Do you encounter any performance issues related to this? If not I would recommend to keep using the retainContextWhenHidden option for now.

[jmenzies12]

Hey @tortmayr,

Thank you very much for the detailed response to this. At the moment we are not encountering any performance issues, we were just reading the Webview docs and noticed the potential downside so wanted to inquire with you about it.

We will continue to use retainContextWhenHidden for now, if it becomes an issue we will get back in touch and see what we can do about it.