RFR: 8296774: Removed default MEMFLAGS value from CHeapBitMap [v2]

[Stefan Karlsson]

On Thu, 10 Nov 2022 10:22:45 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> Today it is easy to accidentally create CHeapBitMaps that uses the default mtInternal MEMFLAGS instead of a value that is suitable for the subsystem. I fixed the instances I could find with #10948 / [JDK-8296231](https://bugs.openjdk.org/browse/JDK-8296231).
>> 
>> For that PR I didn't want to change the constructors of the bitmap because #10941 / [JDK-8296139](https://bugs.openjdk.org/browse/JDK-8296139) was being out for review. Now when that change has been pushed I'd like to change the constructors of the CHeapBitMap, so that we don't accidentally make these mistakes.
>> 
>> When making it mandatory to pass MEMFLAGS, it becomes apparent that the current parameter order is a bit odd. If you look closely you see that all three parameters are optional. When I now want to make MEMFLAGS mandatory, I'd like to move it so that it always is the first parameter. This will simplify the constructors a bit, IMHO.
>> 
>> This is what the constructors look like before the patch:
>> 
>>   CHeapBitMap() : CHeapBitMap(mtInternal) {}
>>   explicit CHeapBitMap(MEMFLAGS flags) : GrowableBitMap(0, false), _flags(flags) {}
>>   CHeapBitMap(idx_t size_in_bits, MEMFLAGS flags = mtInternal, bool clear = true);
>> 
>> 
>> And I'd like to change it to:
>> 
>>   explicit CHeapBitMap(MEMFLAGS flags) : GrowableBitMap(0, false), _flags(flags) {}
>>   CHeapBitMap(MEMFLAGS flags, idx_t size_in_bits, bool clear = true);
>> 
>> 
>> In effect, this makes `flags` mandatory and `size_in_bits` and `clear` optional.
>> 
>> We could probably condense this even further into just one constructor:
>> 
>>   explicit CHeapBitMap(MEMFLAGS flags, size_t size_in_bits = 0, bool clear = true) : GrowableBitMap(size_in_bits, clear), _flags(flags) {}
>> 
>> 
>> given that the value of `clear` doesn't matter when `size_in_bits` is 0. I didn't do that, but could be swayed to do that.
>
> Stefan Karlsson has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'upstream/master' into 8296774_bitmap_stricter_construction
>  - 8296774: Removed default MEMFLAGS value from CHeapBitMap

I got a suggestion in #11086 that I should keep parameter order. I'll do the same for this PR to be consistent between these two collection/utility types.

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PR: https://git.openjdk.org/jdk/pull/11084