There are various situations where we avoid caching things or otherwise take different behavior to prevent race conditions during the parallel servo traversal. Right now we check NS_IsMainThread, but that's overly-general and incurs a TLS lookup. Instead, we should just set a global flag when we begin the traversal (since the main thread is blocked), and clear it when the traversal is complete.

Rearranged things a tiny bit.

Comment on attachment 8833071 [details] [diff] [review] Add a global flag indicating that we're in the servo traversal. v3 I guess this works for now, though how this plays with quantum DOM is less clear to me...

(In reply to Boris Zbarsky [:bz] (still a bit busy) from comment #4) > Comment on attachment 8833071 [details] [diff] [review] > Add a global flag indicating that we're in the servo traversal. v3 > > I guess this works for now, though how this plays with quantum DOM is less > clear to me... That is another bridge to cross at a later point. :-)

And an m-c try push: https://treeherder.mozilla.org/#/jobs?repo=try&revision=eceeed6f236ca1cf2b34c4dfc7e07ae4552bab4a

Pushed by bholley@mozilla.com: https://hg.mozilla.org/integration/mozilla-inbound/rev/93327d92cc47 Add a global flag indicating that we're in the servo traversal. r=bz