1449506 - Clarify AtomMarking synchronisation

Status: RESOLVED FIXED

(Core :: JavaScript: GC, enhancement, P3)

Description

[Jon Coppeard (:jonco)]

The comments in AtomMarkingRuntime say that the table of unused indexes is protected by the GC lock, but the field is wrapped with ExclusiveAccessLockOrGCTaskData<>.  In fact it is only ever accessed with the GC lock held.

Comment 1

[Jon Coppeard (:jonco)]

Attachment: bug1449506-atom-marking-locking

This patch changes the wrapper to GCLockData<> and passes AutoLockGC& through to everything that touches it.  I find the latter helps me to see where locks are held in the code.

I changed the assertions in the methods that update chunk mark bits to ensure that we're in a GC with no helper threads running.  Currently we assert that the current thread holds the exclusive access lock but that's actually a bit of a lie because this is executed on a helper thread while the main thread holds the lock and the assertion somehow allows this.  I'll file for that as well.

For AtomMarkingRuntime::adoptMarkedAtoms we don't need the exclusive access lock at this point.  This is called when merging zones after the source zone has ceased to belong to a helper thread.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/902feab0373f
Clarify AtomMarking locking r=sfink

Comment 3

[Andrei Ciure[:aciure]]

https://hg.mozilla.org/mozilla-central/rev/902feab0373f