RFR: 8253064: monitor list simplifications and getting rid of TSM [v4]

[Coleen Phillimore]

On Tue, 10 Nov 2020 21:12:25 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> src/hotspot/share/runtime/monitorDeflationThread.cpp line 85:
>> 
>>> 83:       // visible to external suspension.
>>> 84: 
>>> 85:       ThreadBlockInVM tbivm(jt);
>> 
>> Does this have to be a JavaThread?  Could it be a non-java thread since deflating monitors doesn't have to call any Java code?  You'd have to lock down the Monitor list maybe, but couldn't this be a NamedThread?  This isn't a request to change it right now.
>
> Ummm... we use a JavaThread because we have to stop async deflation
> during safepoints so that we're not messing with Object headers during GC.
> Yes, it's possible to use a non-JavaThread because this is "just software",
> but I don't want to try to figure out those races...

Ok, I see why it has to be a JavaThread.

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PR: https://git.openjdk.java.net/jdk/pull/642