Page locks up while PDF is being prepared

[jayoshih]

Summary

Jamie: Can't seem to click on stuff and UI becomes locked for a while, with no feedback to the user, until the download modal pops up (Chrome on Ubuntu)

Category

BUG

[rtibbles]

We discussed exactly this as an example of a 'frontend optimization' at the optimizations and reliability team meeting yesterday.

[rtibbles]

I think the way to resolve this is by running the JSPDF code inside a webworker to prevent locking the main thread - the main issue with that is that we need to use the DOM to generate the HTML that we are then turning into a PDF, so we will need to be a little cunning.

Suggested plan:

• Spawn/connect to a webworker where JSPDF is instantiated
• Render the HTML elements in the main thread
• Read from the HTML elements in the main thread
• Transmit via postMessage to the service worker in order to execute the commands
• Do the actual execution of the JSPDF methods inside the web worker
• Return the PDF as a data uri over postMessage

Very simple example to follow here: https://github.com/jstarcher/webworker_jspdf_example/tree/master/js

[jonboiser]

If "PDF is being prepared" refers to the Channel Summary PDF reports, I did not have any problems with that today.

[metodimilevqa]

I'm experiencing the issue under Windows 10 (Chrome, Firefox and Edge) but only with channels rich in resources - 6000+ in my specific case.