1931364 - Screenshots aren't recorded when starting the profiler via StartProfiler from the content process

Status: NEW

(Core :: Gecko Profiler, defect, P2)

Description

[Alexandre Poirot [:ochameau]]

You can start recording JS Tracer from DevTools via the tracer icon on the top right of DevTools:
https://firefox-source-docs.mozilla.org/devtools-user/javascript_tracer/index.html
(you need to toggle a pref for it to appear)

It will then trigger a profiler record from this code:
https://searchfox.org/mozilla-central/rev/30afd6631333bf83d5c62ca48c313d96a21b4bbd/devtools/server/actors/tracer/profiler.js#68-77
calling Services.profiler.StartProfiler from the tab's content process.

But for some reason, this prevents recording page screenshots.
It would be nice if we could make that work.

Moving the call to startProfiler to the parent process is possible, but tricky as it would require to freeze the page execution until we actually start he record from the parent process. Otherwise we would miss some relevant frames when we are using "trace on next page load" or "trace on next user interaction" options.

Comment 1

[Nazım Can Altınova [:canova][:canaltinova on phabricator]]

I think this bug happens because we are not starting the profiler inside the parent process, and only start the profiler in that child process.