Question about trace-IDs

[Roman Kennke]

Hello all,

While studying the code around JFR trace-IDs, I came about something
that I find a little odd: trace-IDs for modules, packages and class-
loaders start at 2, while trace-IDs for threads start at 1 (and classes
at LAST_TYPE_ID+1). The static counters (for modules, packages and
classloaders) are initialized at 1, and the first call to atomic_inc()
increments this to 2 and this is the first value used. I understand
that 0 is the uninitialized value, but don't see that 1 has any special
meaning.

See for example here:
https://github.com/openjdk/jdk/blob/master/src/hotspot/share/jfr/recorder/checkpoint/types/traceid/jfrTraceId.cpp#L65

vs

https://github.com/openjdk/jdk/blob/master/src/hotspot/share/jfr/recorder/checkpoint/types/traceid/jfrTraceId.cpp#L60

Would it hurt to start counting trace-IDs for packages, modules and
classloaders at 1 too? (If not, I'd like to submit a patch - I'm happy
about something simple as my first contributions to JFR ;-) ).

Cheers,
Roman