Crash when using java debugger and kafka

[Aleksey Shipilev]

On 10/30/19 8:42 PM, Roman Kennke wrote:
> Our recent jdk8 development introduced the new barrier model (LRB). I
> tried your testcase with a recent build and it does not happen for me.
> Can you try a suitable build from here:
> 
> https://builds.shipilev.net/openjdk-shenandoah-jdk8/

I actually tried that, and the hang is gone.

I can reproduce the hang with 8u232, it indeed livelocks during Final Mark:

Heuristics ergonomically sets -XX:+ShenandoahImplicitGCInvokesConcurrent
Trigger: Metadata GC Threshold
2.361: [Concurrent reset 88128K->88128K(2016M), 2.955 ms]
2.364: [Pause Init Mark (process weakrefs) (unload classes), 6.880 ms]
2.371: [Concurrent marking (process weakrefs) (unload classes) 88128K->89152K(2016M), 5.414 ms]
2.376: [Concurrent precleaning 89152K->89152K(2016M), 1.677 ms]
2.378: [Pause Final Mark (process weakrefs) (unload classes)

...when doing JvmtiTagMap::weak_oops_do. I might study how that happens in 8u232, to make sure head
sh/jdk8 does not work by accident.

Anyhow, given this is the weak root scanning problem, here is the workaround: -XX:-ClassUnloading.
The hang disappears on 8u232 for me with disabled class unloading.

-- 
Thanks,
-Aleksey