1434615 - Schemas.jsm seems to be doing startup main thread IO with NetUtil.asyncFetch

Status: RESOLVED WONTFIX

(WebExtensions :: Untriaged, enhancement)

Description

[Florian Quèze [:florian]]

https://perfht.ml/2rSUPsN is a startup profile where NetUtil_asyncFetch called by readJSON from resource://gre/modules/Schemas.jsm seems to be doing main thread I/O.

https://groups.google.com/forum/#!topic/mozilla.dev.platform/_N88WYP4ZmQ was saying:
"Q: Aren't NetUtils.asyncFetch and NetUtils.asyncCopy sufficient?
A1: Most uses of NetUtils.asyncCopy I have seen seem to actually perform
some main thread file I/O behind the scenes."

So NetUtil_asyncFetch being something to avoid doesn't seem to be something new. Could https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API be used instead?

While it's not visible in my profile, https://searchfox.org/mozilla-central/rev/c56f656febb1aa58c72b218699e24a76425bd284/toolkit/components/extensions/Extension.jsm#410 seems to have the same code.

Comment 1

[Kris Maglione [:kmag]]

This code is only used when the schema data isn't already in the startup cache, and there's already a bug to fix asyncFetch to not do main thread IO for jar channels.