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

[Markus Grönlund]

On Wed, 4 Jan 2023 14:24:31 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

>> 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.

The reason for asking is for upcoming changes that try to minimize everything involved in sampling. Is this only needed for virtual threads?

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