RFR: 8294308: Allow dynamically choosing the MEMFLAGS of a type without ResourceObj [v2]

[Kim Barrett]

On Sat, 24 Sep 2022 09:47:38 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> src/hotspot/share/memory/allocation.hpp line 219:
>> 
>>> 217: };
>>> 218: 
>>> 219: class DynCHeapObj {
>> 
>> I tried this and it seems to work:  If you make CHeapObj new operators take MEMFLAGS f = F, where F is the default  value, you could not have this class and make outputStream inherit from CHeapObj<mtInternal\> and the new calls will override mtInternal.  I guess the risk is that you get mtInternal if you forget the parameter to new.
>
> Good idea! I implemented this instead.

We can eliminate this problem:
"I guess the risk is that you get mtInternal if you forget the parameter to new."

We can instead have CHeapObj<mtFoo> that *only* allocates with mtFoo, and
CHeapObj<> that *requires* specifying the flag when allocating the memory. (I
did something like this for the CHeapAllocator in my prototype for Standard
Library usage.) As part of that, we can also have the MEMFLAGS argument (when
needed) always be the first argument in the placement list.

Very(!) lightly tested:
https://github.com/kimbarrett/openjdk-jdk/tree/dynamic-memflags

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PR: https://git.openjdk.org/jdk/pull/10412