Ensure new non-main threads have their names set

[jamienicol]

Before: https://share.firefox.dev/3Ui2gF8 After: https://share.firefox.dev/4aSsmny

Ignore the "Thread-2", "Thread-3" etc in the after profile. Those are indeed the "correct" names due to https://bugzilla.mozilla.org/show_bug.cgi?id=1891726

[mstange]

Oh yeah, this looks like an oversight.

I think this wasn't needed on Linux for the following reasons:

• For new threads, we first inherit the name from the parent (while handling FORK records) and then update the name once we see the COMM record.
• For existing threads when samply record does the profiling, we call register_existing_thread with the name from /proc/{pid}/task/{tid}/comm.
• For existing threads when perf record does the profiling, perf synthesizes COMM events at the start of the trace.

So it seems either simpleperf does not synthesize COMM events, or maybe it puts the "thread map" in a different place.

Anyway, this change looks like a clear improvement, merging.

[mstange]

So it seems either simpleperf does not synthesize COMM events, or maybe it puts the "thread map" in a different place.

It seems the COMM events are there, but the MMAP2 events come first, so the thread already exists by the time we see the COMM events.