1752930 - Record information about past child processes' exit profiles

Status: NEW

(Core :: Gecko Profiler, task, P3)

Description

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

Thanks to bug 1673513, the parent process now waits for slow processes to send their profile (by regularly requesting progress updates).
If at some point, pending processes don't make any more progress (either they don't respond at all, or they report the same progress value as before), the parent profile gives up and considers the overall profile complete.

If that happens, it would be good to record some information about these missing sub-profiles, to eventually show this in the front-end.
Also tests could check for that if they don't find the expected sub-profile in the main "processes" array, and then either try again or report a more informative failure.

Details:
I can think of two options to record this information in the final json profile:

1. Add a new json object at the root, containing post-gathering data, including process information for those that failed to gather their profile.
2. Inside the existing "processes" array, generate a stand-in object for that process, with as much information as possible, and flagging that the actual sub-profile is missing. (But this may be confusing to the front-end processor that would expect a full profile there.)

Comment 1

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

Bug 1779685 added information in profile.profileGatheringLog, including which processes failed to respond when gathering a profile.

I'm keeping this bug open, because we still don't record useful information about past child processes, whether there was no exit profile, or that profile could not be integrated (e.g., for size reasons, see bug 1758643 patch D152026).