1733970 - Strengthen invariants around access to per-tier information

Status: RESOLVED FIXED

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

Description

[Lars T Hansen [:lth]]

+++ This bug was initially created as a clone of Bug #1733908 +++

In bug 1733908, it was discovered that some of the invariants around access to Code::tier2_ were not obeyed in certain situations where it was actually but not obviously safe not to do so. We can and should clean this up properly.

Comment 1

[Lars T Hansen [:lth]]

Attachment: Bug 1733970 - Strengthen invariant on Code::tier2_. r?jseward

It is an invariant of Code::tier2_ that it is never read without the
atomic Code::hasTier2_ being true.

This invariant is violated in a couple of harmless cases, where code
on the thread that has just written tier2_ (the committing background
thread) will read tier2_ again before the tier-2 code is committed by
hasTier2_ being written.

This patch removes those violations at essentially zero cost.

TODO: I added a protocol here for setTier2 to return a borrowed
pointer to the tier-2 code. But it's possible that the caller of
setTier2 should just extract that pointer from values it already has
in hand. Discuss.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/51ad19d01a3a
Strengthen invariant on Code::tier2_. r=jseward

Comment 3

[Natalia Csoregi [:nataliaCs]]

https://hg.mozilla.org/mozilla-central/rev/51ad19d01a3a