RFR: 8298377: JfrVframeStream causes deadlocks in ZGC [v2]

[Erik Österlund]

On Tue, 3 Jan 2023 13:53:43 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

> The upshot with this solution compared to not having stacktraces for the ZPage Allocation Event is that only the relocation parts are sensitive? Other allocation sites can still have stacktraces?

It's even more precise than that. Only relocation events... specifically when processing the stack watermark of the current thread, needs to emit stack traces. Any other relocation event can still print stack traces, and other allocation events as well.

> src/hotspot/share/jfr/periodic/sampling/jfrThreadSampler.cpp line 391:
> 
>> 389: 
>> 390:   bool ret = false;
>> 391:   StackWatermarkSet::start_processing(thread, StackWatermarkKind::gc);
> 
> Is this now needed unconditionally, for all threads sampled? What is the overhead of introducing it?

Compared to everything else that thread sampling does, I really wouldn't worry about it. In the common case it will just check if processing already started, and then continue.

-------------

PR: https://git.openjdk.org/jdk/pull/11778