RFR: 8283710: JVMTI: Use BitSet for object marking

[Thomas Stuefe]

On Fri, 8 Apr 2022 02:01:50 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> > > One open question is which MEMFLAGS to use. mtTracing doesn't seem to be exactly right. Should I templatize BitSet and make JVMTI use mtServiceability and JRF use mtTracing as it did before?
> > 
> > 
> > Yes, I think templatizing for MEMFLAGS makes sense (concurrentHashTable.hpp is too).
> 
> I haven't had time to look at the code, but I don't know about this. Slapping a template parameter on everything isn't necessarily a good idea. We recently (JDK-8283368) undid exactly this sort of thing in the cardset code, instead making the MEMFLAGS value a runtime parameter provided at construction time. This avoids a bunch of generated code duplication, additional template syntax, and allows more implementation be put in .cpp files because it isn't a template.

I never liked MEMFLAGS as template parameter. A runtime parameter would it make easier to use a general-purpose data structure on behalf of a subsystem and account its memory to that subsystem, while still being able to pass it around as a simple pointer to other utility functions.

But here Roman squirreled the template definition away into a typedef, so I think we could cleanup MEMFLAG usage in a separate RFE?

(we also should move MEMFLAGS to an own header file, btw, to avoid having to pull allocation.hpp every time)

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PR: https://git.openjdk.java.net/jdk/pull/7964