Size of async javascript queue (in Vaadin 8)

I have a real-time app which streams data to the browser. Sometimes lots of updates are sent, which can take a while to transfer.
It’s a map app, and it’s not unusual for the application to want to update 1000s of objects on-screen at a time.

This causes an interactivity problem. Whilst the data is streaming, the UI is unresponsive for the user.

I’d like the app to be able to see if there are any outstanding requests to be sent to the browser, so that it can determine the rate at which it should send them. I am hoping to make space for general UI updates to be made and for user interactions to be received, amidst the bulk object flow.

Is there a way for the app to query the state of the server/client interaction to determine how many requests are queued?

Thanks!

Joe