1711246 - OSPreferences::GetInstanceAddRefed() is not safe to call off-main-thread

Status: RESOLVED FIXED

(Core :: Internationalization, defect)

Description

[Jonathan Kew [:jfkthame]]

The method gfxDWriteFontFamily::LocalizedName uses OSPreferences::GetInstanceAddRefed to get a reference to the preferences service; but LocalizedName may be called off-main-thread, which is bad because OSPreferences doesn't use thread-safe refcounting.

The bug can be demonstrated by running a debug Windows build with gfx.e10s.font-list.shared set to false, and then opening about:preferences. The thread that intends to populate the Font menu will crash with a thread-safety assertion.

In practice it seems highly unlikely this would cause problems, although maybe opening Preferences and then instantly shutting down the browser might possibly cause a race resulting in incorrect behavior (e.g. a leak or a double-free of the OSPreferences singleton). Nevertheless, we should fix it to avoid any risk.

Comment 1

[Jonathan Kew [:jfkthame]]

Attachment: Bug 1711246 - Make OSPreferences refcounting thread-safe, because of potential OMT usage from gfxDWriteFontFamily. r=#platform-i18n-reviewers

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/76dd6379cc01
Make OSPreferences refcounting thread-safe, because of potential OMT usage from gfxDWriteFontFamily. r=dminor

Comment 3

[Dorel Luca [:dluca]]

https://hg.mozilla.org/mozilla-central/rev/76dd6379cc01