839471 - GC: Sweep type objects on the background thread

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement)

Description

[Jon Coppeard (:jonco)]

Following on from sweeping shapes and baseshapes on the background thread, we can do the same for type objects.

One issue however is that TypeCompartment::markSetsUnknown() iterates over all type objects in the compartment.  Previously this was disallowed for thing kinds that were background finalized, as the other thread may be updating the heap data structures at the same time.

I've changed this so that for background finalized kinds CellIter waits for the background thread to finish sweeping if it is currently doing so.  No GC slice can occur while we are iterating, and this is asserted in debug builds, so I think this is safe.

This is a potential source of pauses, however I don't think it gets called that often in practice.

Comment 1

[Jon Coppeard (:jonco)]

Attachment: Proposed fix

Comment 2

[Jon Coppeard (:jonco)]

Try build here - looking good so far:

https://tbpl.mozilla.org/?tree=Try&rev=cbabf5b94168

Comment 3

[Jon Coppeard (:jonco)]

https://hg.mozilla.org/integration/mozilla-inbound/rev/16ddbb6852ec

Comment 4

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/16ddbb6852ec