High CPU load when many messages occurred in browser console

[snemh]

High CPU load when many messages occurred in browser console. When there is huge number of warnings generated, testem tries to process and print each message in a loop, causing high CPU load which eventually causes the processes to crash.

[kratiahuja]

@snemh would be good to add a failing test case or reproduction first to show the problem and then we can see how to fix it.

cc: @stefanpenner (Thank you Stef for helping recognizing the root cause)

[stefanpenner]

Concretely, it appears the architecture of message syncing/formating/printing between split_log_panel and scrollable-text-panel is not scalable. These code-paths must operate on the entire message history, so as the number of messages (app warnings) increase, testem slows down (and node/ember CPU time increase) as the message history grows. As observed in @snemh this can quickly lead to a totally locked up process.

In the example @snemh, it looked like we where operating at over 130,000 lines of text.

These code-paths will need to be changed. Although the changes are relatively straight forward, it will take some effort to accomplish them and I don't personally have extra bandwidth to implement. Although I will gladly provide code-review/guidance to those able to do the majority of the work.

[runspired]

Until this is fixed, if you don't care about these logs (I suspect most of us don't) you can free up a lot of memory and cpu by preventing testem from serializing these and emitting them.

<script src="/testem.js" integrity="" data-embroider-ignore></script>
<script type="text/javascript">
	// disable testem log output
	// by default testem serializes all of these logs
	// and transmits them through the websocket even if
	// the reporter is configured to ignore them. This results
	// in extremely high memory and cpu utilization and eventually
	// will crash the console.
	const ignoredLogTypes = new Set(['log', 'warn', 'info', 'group']);
	// restore original functionality
	ignoredLogTypes.forEach((method) => {
		console[method] = Testem.console[method];
	});
</script>