RFR: 8256811: Delayed/missed jdwp class unloading events [v4]

[Zhengyu Gu]

On Mon, 27 Jun 2022 15:50:47 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> src/hotspot/share/prims/jvmtiTagMap.cpp line 1200:
>> 
>>> 1198: };
>>> 1199: 
>>> 1200: // PostObjectFree can't be called by JavaThread, so call it from the VM thread.
>> 
>> I wish I'd written why here.  I think it's because we can't hold a Mutex to do the callback, but now I don't remember. I need to spend some time to understand this.  Thanks @plummercj  for adding Kim and I.
>
> Ok, thanks I reread your description and see it now.  At this point, you are neither holding the Mutex and have already collected the objects, so that you can transition to native.

Yes.

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PR: https://git.openjdk.org/jdk/pull/9168