RFR: 8212879: Make JVMTI TagMap table concurrent [v3]

[Coleen Phillimore]

On Tue, 3 Nov 2020 21:47:24 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> src/hotspot/share/gc/shared/weakProcessorPhases.hpp line 50:
>> 
>>> 48: };
>>> 49: 
>>> 50: typedef uint WeakProcessorPhase;
>> 
>> This was originally written with the idea that WeakProcessorPhases::Phase (and WeakProcessorPhase) should be a scoped enum (but we didn't have that feature yet). It's possible there are places that don't cope with a scoped enum, since that feature wasn't available when the code was written, so there might have be mistakes.
>> 
>> But because of that, I'd prefer to keep the WeakProcessorPhases::Phase type and the existing definition of WeakProcessorPhase. Except this proposed change is breaking that at least here:
>> 
>> src/hotspot/share/gc/shared/weakProcessor.inline.hpp
>> 116     uint oopstorage_index = WeakProcessorPhases::oopstorage_index(phase);
>> 117     StorageState* cur_state = _storage_states.par_state(oopstorage_index);
>> =>
>> 103     StorageState* cur_state = _storage_states.par_state(phase);
>> 
>> I think eventually (as in some future RFE) this could all be collapsed to something provided by OopStorageSet.
>> enum class : uint WeakProcessorPhase {}; 
>> 
>> ENUMERATOR_RANGE(WeakProcessorPhase,
>>                  static_cast<WeakProcessorPhase>(0), 
>>                  static_cast<WeakProcessorPhase>(OopStorageSet::weak_count));
>> and replacing all uses of WeakProcessorPhases::Iterator with EnumIterator<WeakProcessorPhase> (which involves more than a type alias).
>> 
>> Though it might be possible to go even further and eliminate WeakProcessorPhases as a thing separate from OopStorageSet.
>
> Ok, so I'm not sure what to do with this:
> 
>  enum Phase { 
>     // Serial phase.
>     JVMTI_ONLY(jvmti)
>     // Additional implicit phase values follow for oopstorages.
>   `};`
> 
> I've removed the only thing in this enum.

>Though it might be possible to go even further and eliminate WeakProcessorPhases as a thing separate from OopStorageSet.

This makes sense.  Can we file another RFE for this? I was sort of surprised by how much code was involved so I tried to find a place to stop deleting.

-------------

PR: https://git.openjdk.java.net/jdk/pull/967