1745318 - Add `MOZ_ASSERT_IF(XRE_IsParentProcess(), NS_IsMainThread())` in `StreamMetaJSCustomObject()`

Status: RESOLVED FIXED

(Core :: Gecko Profiler, task, P2)

Description

[Gerald Squelart (he/him) (not at Mozilla since 2022-09-15)]

If a developer tries to generate a profile from a non-main thread, it looks like it works fine, but the profile is actually incomplete, because we don't include all the necessary data in that case, which normally happens in child processes where such redundant data is not needed: https://searchfox.org/mozilla-central/rev/9028b0458cc1f432870d2996b186b0938dda734a/tools/profiler/core/platform.cpp#2640-2650

To avoid this confusing situation, it may be worth adding a hard check like MOZ_ASSERT_IF(XRE_IsParentProcess(), NS_IsMainThread()), with some explanations, so that it will be immediately obvious that this is the wrong thing to do, and such call should be dispatched to the main thread.

(This main-thread limitation is due to the need to call some APIs that only work from the main thread, like services::GetObserverService().)

Comment 1

[Gerald Squelart (he/him) (not at Mozilla since 2022-09-15)]

Attachment: Bug 1745318 - In the parent process, assert that profiles are only generated on the main thread - r?mstange

This is to avoid situations where a developer may call this from another thread, and get a confusingly incomplete profile.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/23777ea03332
In the parent process, assert that profiles are only generated on the main thread - r=mstange

Comment 3

[Alexandru Michis [:malexandru]]

https://hg.mozilla.org/mozilla-central/rev/23777ea03332