549543 - Extend eval cache to cache setTimeout programs

Status: NEW

(Core :: JavaScript Engine, enhancement, P5)

Description

[Brendan Eich [:brendan]]

From a shark sample on my 100%-cpu-consuming Namoroka:

	2.9%	2.9%	libmozjs.dylib	JS_DHashTableEnumerate
	0.0%	2.7%	libmozjs.dylib	 js_PurgeScriptFragments(JSContext*, JSScript*)
	0.0%	2.7%	libmozjs.dylib	  js_DestroyScript
	0.0%	2.7%	libmozjs.dylib	   JS_EvaluateUCScriptForPrincipals
	0.0%	2.7%	XUL	    nsJSContext::EvaluateString(nsAString_internal const&, void*, nsIPrincipal*, char const*, unsigned int, unsigned int, nsAString_internal*, int*)
	0.0%	2.7%	XUL	     nsGlobalWindow::RunTimeout(nsTimeout*)
	0.0%	2.7%	XUL	      nsGlobalWindow::TimerCallback(nsITimer*, void*)
	0.0%	2.7%	XUL	       nsTimerImpl::Fire()

This needs some dedicated API, since we do not want to blow out the cache due to any and all JS_Evaluate*Script* API calls, only ones for programs likely to be repeatedly compiled and executed (setTimeout, setInterval with string first arg).

Who will take this bug? It is crying for a fix.

/be

Comment 1

[Sylvestre Ledru [:Sylvestre]]

Moving to p3 because no activity for at least 1 year(s).
See https://github.com/mozilla/bug-handling/blob/master/policy/triage-bugzilla.md#how-do-you-triage for more information

Comment 2

[Matthew Gaudet (he/him) [:mgaudet]]

(Realistically this needs to be motivated again if we wanted to do this)

Comment 3

[Mayank Bansal]

relevant for JetStream3?

Comment 4

[Iain Ireland [:iain]]

As I understand it, this is about setTimeout("some string") and setInterval("some string"), both of which MDN marks as "not recommended". I don't think this specific problem shows up in JetStream.

That said, it looks to me like it is still a potential problem. If I'm tracing through the DOM code correctly, both setTimeout and setInterval bottom out here (window) and here (worker), and AFAICT neither case ends up looking at the eval cache.

As Matt says, though, I think we'd need to see a real-world example where this is hot to fix it now.