[foreign-jextract] RFR: MemorySegmentPool + Allocator [v8]

[Maurizio Cimadamore]

On Thu, 22 Apr 2021 01:53:10 GMT, Radoslaw Smogura <github.com+7535718+rsmogura at openjdk.org> wrote:

>> (Preview)
>> 
>> The MemorySegmentPool is a pool maintaining memory segments, optionally can expose allocator which can be bound to other scope, and which will return allocated segments back to pool.
>> 
>> However the best results has been achieved by using getSegmentEntry & putSegmentEntry methods.
>> 
>> The pool is intended to be used by long running applications (i.e. like global shared pool), where fast allocation and de-allocation of segments is critical (was designed during implementation of I/O subsystem with Panama, as a pool for temporary buffers between system I/O methods and Java byte arrays from InputStreams).
>> 
>> The pool uses hand-made SpinLockQueue as the Deque from JDK offers too much functionality and overhead.
>
> Radoslaw Smogura has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Tests better distribute sizes for pseudo random allocation - now much larger buffers gets allocated and used.
>   
>   I'm bit puzzled here, as it looks like, that allocatioin is very fast, only
>   reading is extreme slow.
>   
>   For comparision when processing single allocation:
>   Update only first byte: direct pool access - 33ns, malloc / free: 59ns
>   Update very 1024th byte: 12980ns, vs malloc: 8400ns
>   
>   I think simillar results has been spot during test with StringLen.

test/micro/org/openjdk/bench/jdk/incubator/foreign/AllocatorsForLongRun.java line 162:

> 160:     for (int idx = 0; idx <  size; idx += 1024) {
> 161: //      MemoryAccess.setByteAtOffset(s, l, (byte)0);
> 162:       BYTE.set(s, 0, (byte) 1);

You need to cast the offset (idx?) back to a long when you call BYTE.set, otherwise the var handle invocation is not exact.

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PR: https://git.openjdk.java.net/panama-foreign/pull/509