RFR: 8345687: Improve the implementation of SegmentFactories::allocateSegment [v3]

[Quan Anh Mai]

On Mon, 16 Dec 2024 11:01:11 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Quan Anh Mai has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - wrong init
>>  - move segment instance creation to SegmentFactories
>
> test/micro/org/openjdk/bench/java/lang/foreign/AllocTest.java line 77:
> 
>> 75:             var freeAddr = lookup.findOrThrow("free");
>> 76:             CALLOC = linker.downcallHandle(callocAddr, FunctionDescriptor.of(ValueLayout.JAVA_LONG, ValueLayout.JAVA_LONG, ValueLayout.JAVA_LONG));
>> 77:             FREE = linker.downcallHandle(freeAddr, FunctionDescriptor.ofVoid(ValueLayout.JAVA_LONG));
> 
> I'm not sure these changes are needed. It seems the main goal here is to avoid the cost of the capture associated with `CLayouts::freeMemory` ? If so, can't we just store that consumer into a static final and call it a day? I think then we could avoid the `static` init, and leave most of the code unchanged, except for the additional static field?

The main goal here is that passing/receiving raw addresses as longs is cheaper than as `MemorySegment`s.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22610#discussion_r1925646301