1973095 - CallSetup should interact with the GC more efficiently.

Status: NEW

(Core :: DOM: Core & HTML, enhancement)

Description

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

Basically, Rooting while cheap, isn't free. CallSetup contains 3 Rooted fields, and is often used around a 4th.

There are some options for fixing this, but none quite so simple that it's trivial for me to do otherwise this would have a patch attached already.

Option 1: Replace Rooted with RootedTuple and RootedField. We've done this in the engine for helpers and seen a 5% improvement on a subtest of JetStream3.

This comes at a slight cost however of adding a new member to CallSetup; the gymnastics required to maintain the mozilla::Maybe rig that exists here.

Option 2: Root CallSetup and add a trace function. I'd actually strongly prefer this, but the setup story for CallSetup is very awkward because it wants to do some pre-flight checks before trying for a JSContext. I soft of would love it if there was a way for us to have a JSContext around for CallSetup or to split the preflight checks.

Opening this bug for discussion.

Comment 1

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

Attachment: WIP: Bug 1973095 - Use RootedTuple inside of CallSetup

Comment 2

[Olli Pettay [:smaug][[e-mail]]]

I don't know what is awkward in CallSetup (seems quite ok, given what the platform requires), but both 1 and 2 feel ok to me.
(RootedTuple is a bit ugly, since RootedField takes then some magical numbers, but perhaps that is fine.)